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diff --git a/sql/debug_sync.cc b/sql/debug_sync.cc
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+/* Copyright (C) 2008 MySQL AB, 2008 - 2009 Sun Microsystems, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+/**
+  == Debug Sync Facility ==
+
+  The Debug Sync Facility allows placement of synchronization points in
+  the server code by using the DEBUG_SYNC macro:
+
+      open_tables(...)
+
+      DEBUG_SYNC(thd, "after_open_tables");
+
+      lock_tables(...)
+
+  When activated, a sync point can
+
+    - Emit a signal and/or
+    - Wait for a signal
+
+  Nomenclature:
+
+    - signal:             A value of a global variable that persists
+                          until overwritten by a new signal. The global
+                          variable can also be seen as a "signal post"
+                          or "flag mast". Then the signal is what is
+                          attached to the "signal post" or "flag mast".
+
+    - emit a signal:      Assign the value (the signal) to the global
+                          variable ("set a flag") and broadcast a
+                          global condition to wake those waiting for
+                          a signal.
+
+    - wait for a signal:  Loop over waiting for the global condition until
+                          the global value matches the wait-for signal.
+
+  By default, all sync points are inactive. They do nothing (except to
+  burn a couple of CPU cycles for checking if they are active).
+
+  A sync point becomes active when an action is requested for it.
+  To do so, put a line like this in the test case file:
+
+      SET DEBUG_SYNC= 'after_open_tables SIGNAL opened WAIT_FOR flushed';
+
+  This activates the sync point 'after_open_tables'. It requests it to
+  emit the signal 'opened' and wait for another thread to emit the signal
+  'flushed' when the thread's execution runs through the sync point.
+
+  For every sync point there can be one action per thread only. Every
+  thread can request multiple actions, but only one per sync point. In
+  other words, a thread can activate multiple sync points.
+
+  Here is an example how to activate and use the sync points:
+
+      --connection conn1
+      SET DEBUG_SYNC= 'after_open_tables SIGNAL opened WAIT_FOR flushed';
+      send INSERT INTO t1 VALUES(1);
+          --connection conn2
+          SET DEBUG_SYNC= 'now WAIT_FOR opened';
+          SET DEBUG_SYNC= 'after_abort_locks SIGNAL flushed';
+          FLUSH TABLE t1;
+
+  When conn1 runs through the INSERT statement, it hits the sync point
+  'after_open_tables'. It notices that it is active and executes its
+  action. It emits the signal 'opened' and waits for another thread to
+  emit the signal 'flushed'.
+
+  conn2 waits immediately at the special sync point 'now' for another
+  thread to emit the 'opened' signal.
+
+  A signal remains in effect until it is overwritten. If conn1 signals
+  'opened' before conn2 reaches 'now', conn2 will still find the 'opened'
+  signal. It does not wait in this case.
+
+  When conn2 reaches 'after_abort_locks', it signals 'flushed', which lets
+  conn1 awake.
+
+  Normally the activation of a sync point is cleared when it has been
+  executed. Sometimes it is necessary to keep the sync point active for
+  another execution. You can add an execute count to the action:
+
+      SET DEBUG_SYNC= 'name SIGNAL sig EXECUTE 3';
+
+  This sets the signal point's activation counter to 3. Each execution
+  decrements the counter. After the third execution the sync point
+  becomes inactive.
+
+  One of the primary goals of this facility is to eliminate sleeps from
+  the test suite. In most cases it should be possible to rewrite test
+  cases so that they do not need to sleep. (But this facility cannot
+  synchronize multiple processes.) However, to support test development,
+  and as a last resort, sync point waiting times out. There is a default
+  timeout, but it can be overridden:
+
+      SET DEBUG_SYNC= 'name WAIT_FOR sig TIMEOUT 10 EXECUTE 2';
+
+  TIMEOUT 0 is special: If the signal is not present, the wait times out
+  immediately.
+
+  When a wait timed out (even on TIMEOUT 0), a warning is generated so
+  that it shows up in the test result.
+
+  You can throw an error message and kill the query when a synchronization
+  point is hit a certain number of times:
+
+      SET DEBUG_SYNC= 'name HIT_LIMIT 3';
+
+  Or combine it with signal and/or wait:
+
+      SET DEBUG_SYNC= 'name SIGNAL sig EXECUTE 2 HIT_LIMIT 3';
+
+  Here the first two hits emit the signal, the third hit returns the error
+  message and kills the query.
+
+  For cases where you are not sure that an action is taken and thus
+  cleared in any case, you can force to clear (deactivate) a sync point:
+
+      SET DEBUG_SYNC= 'name CLEAR';
+
+  If you want to clear all actions and clear the global signal, use:
+
+      SET DEBUG_SYNC= 'RESET';
+
+  This is the only way to reset the global signal to an empty string.
+
+  For testing of the facility itself you can execute a sync point just
+  as if it had been hit:
+
+      SET DEBUG_SYNC= 'name TEST';
+
+
+  === Formal Syntax ===
+
+  The string to "assign" to the DEBUG_SYNC variable can contain:
+
+      {RESET |
+       <sync point name> TEST |
+       <sync point name> CLEAR |
+       <sync point name> {{SIGNAL <signal name> |
+                           WAIT_FOR <signal name> [TIMEOUT <seconds>]}
+                          [EXECUTE <count>] &| HIT_LIMIT <count>}
+
+  Here '&|' means 'and/or'. This means that one of the sections
+  separated by '&|' must be present or both of them.
+
+
+  === Activation/Deactivation ===
+
+  The facility is an optional part of the MySQL server.
+  It is enabled in a debug server by default.
+
+      ./configure --enable-debug-sync
+
+  The Debug Sync Facility, when compiled in, is disabled by default. It
+  can be enabled by a mysqld command line option:
+
+      --debug-sync-timeout[=default_wait_timeout_value_in_seconds]
+
+  'default_wait_timeout_value_in_seconds' is the default timeout for the
+  WAIT_FOR action. If set to zero, the facility stays disabled.
+
+  The facility is enabled by default in the test suite, but can be
+  disabled with:
+
+      mysql-test-run.pl ... --debug-sync-timeout=0 ...
+
+  Likewise the default wait timeout can be set:
+
+      mysql-test-run.pl ... --debug-sync-timeout=10 ...
+
+  The command line option influences the readable value of the system
+  variable 'debug_sync'.
+
+  * If the facility is not compiled in, the system variable does not exist.
+
+  * If --debug-sync-timeout=0 the value of the variable reads as "OFF".
+
+  * Otherwise the value reads as "ON - current signal: " followed by the
+    current signal string, which can be empty.
+
+  The readable variable value is the same, regardless if read as global
+  or session value.
+
+  Setting the 'debug-sync' system variable requires 'SUPER' privilege.
+  You can never read back the string that you assigned to the variable,
+  unless you assign the value that the variable does already have. But
+  that would give a parse error. A syntactically correct string is
+  parsed into a debug sync action and stored apart from the variable value.
+
+
+  === Implementation ===
+
+  Pseudo code for a sync point:
+
+      #define DEBUG_SYNC(thd, sync_point_name)
+                if (unlikely(opt_debug_sync_timeout))
+                  debug_sync(thd, STRING_WITH_LEN(sync_point_name))
+
+  The sync point performs a binary search in a sorted array of actions
+  for this thread.
+
+  The SET DEBUG_SYNC statement adds a requested action to the array or
+  overwrites an existing action for the same sync point. When it adds a
+  new action, the array is sorted again.
+
+
+  === A typical synchronization pattern ===
+
+  There are quite a few places in MySQL, where we use a synchronization
+  pattern like this:
+
+  pthread_mutex_lock(&mutex);
+  thd->enter_cond(&condition_variable, &mutex, new_message);
+  #if defined(ENABLE_DEBUG_SYNC)
+  if (!thd->killed && !end_of_wait_condition)
+     DEBUG_SYNC(thd, "sync_point_name");
+  #endif
+  while (!thd->killed && !end_of_wait_condition)
+    pthread_cond_wait(&condition_variable, &mutex);
+  thd->exit_cond(old_message);
+
+  Here some explanations:
+
+  thd->enter_cond() is used to register the condition variable and the
+  mutex in thd->mysys_var. This is done to allow the thread to be
+  interrupted (killed) from its sleep. Another thread can find the
+  condition variable to signal and mutex to use for synchronization in
+  this thread's THD::mysys_var.
+
+  thd->enter_cond() requires the mutex to be acquired in advance.
+
+  thd->exit_cond() unregisters the condition variable and mutex and
+  releases the mutex.
+
+  If you want to have a Debug Sync point with the wait, please place it
+  behind enter_cond(). Only then you can safely decide, if the wait will
+  be taken. Also you will have THD::proc_info correct when the sync
+  point emits a signal. DEBUG_SYNC sets its own proc_info, but restores
+  the previous one before releasing its internal mutex. As soon as
+  another thread sees the signal, it does also see the proc_info from
+  before entering the sync point. In this case it will be "new_message",
+  which is associated with the wait that is to be synchronized.
+
+  In the example above, the wait condition is repeated before the sync
+  point. This is done to skip the sync point, if no wait takes place.
+  The sync point is before the loop (not inside the loop) to have it hit
+  once only. It is possible that the condition variable is signaled
+  multiple times without the wait condition to be true.
+
+  A bit off-topic: At some places, the loop is taken around the whole
+  synchronization pattern:
+
+  while (!thd->killed && !end_of_wait_condition)
+  {
+    pthread_mutex_lock(&mutex);
+    thd->enter_cond(&condition_variable, &mutex, new_message);
+    if (!thd->killed [&& !end_of_wait_condition])
+    {
+      [DEBUG_SYNC(thd, "sync_point_name");]
+      pthread_cond_wait(&condition_variable, &mutex);
+    }
+    thd->exit_cond(old_message);
+  }
+
+  Note that it is important to repeat the test for thd->killed after
+  enter_cond(). Otherwise the killing thread may kill this thread after
+  it tested thd->killed in the loop condition and before it registered
+  the condition variable and mutex in enter_cond(). In this case, the
+  killing thread does not know that this thread is going to wait on a
+  condition variable. It would just set THD::killed. But if we would not
+  test it again, we would go asleep though we are killed. If the killing
+  thread would kill us when we are after the second test, but still
+  before sleeping, we hold the mutex, which is registered in mysys_var.
+  The killing thread would try to acquire the mutex before signaling
+  the condition variable. Since the mutex is only released implicitly in
+  pthread_cond_wait(), the signaling happens at the right place. We
+  have a safe synchronization.
+
+  === Co-work with the DBUG facility ===
+
+  When running the MySQL test suite with the --debug command line
+  option, the Debug Sync Facility writes trace messages to the DBUG
+  trace. The following shell commands proved very useful in extracting
+  relevant information:
+
+  egrep 'query:|debug_sync_exec:' mysql-test/var/log/mysqld.1.trace
+
+  It shows all executed SQL statements and all actions executed by
+  synchronization points.
+
+  Sometimes it is also useful to see, which synchronization points have
+  been run through (hit) with or without executing actions. Then add
+  "|debug_sync_point:" to the egrep pattern.
+
+  === Further reading ===
+
+  For a discussion of other methods to synchronize threads see
+  http://forge.mysql.com/wiki/MySQL_Internals_Test_Synchronization
+
+  For complete syntax tests, functional tests, and examples see the test
+  case debug_sync.test.
+
+  See also worklog entry WL#4259 - Test Synchronization Facility
+*/
+
+#include "debug_sync.h"
+
+#if defined(ENABLED_DEBUG_SYNC)
+
+/*
+  Due to weaknesses in our include files, we need to include
+  mysql_priv.h here. To have THD declared, we need to include
+  sql_class.h. This includes log_event.h, which in turn requires
+  declarations from mysql_priv.h (e.g. OPTION_AUTO_IS_NULL).
+  mysql_priv.h includes almost everything, so is sufficient here.
+*/
+#include "mysql_priv.h"
+
+/*
+  Action to perform at a synchronization point.
+  NOTE: This structure is moved around in memory by realloc(), qsort(),
+        and memmove(). Do not add objects with non-trivial constuctors
+        or destructors, which might prevent moving of this structure
+        with these functions.
+*/
+struct st_debug_sync_action
+{
+  ulong         activation_count;       /* max(hit_limit, execute) */
+  ulong         hit_limit;              /* hits before kill query */
+  ulong         execute;                /* executes before self-clear */
+  ulong         timeout;                /* wait_for timeout */
+  String        signal;                 /* signal to emit */
+  String        wait_for;               /* signal to wait for */
+  String        sync_point;             /* sync point name */
+  bool          need_sort;              /* if new action, array needs sort */
+};
+
+/* Debug sync control. Referenced by THD. */
+struct st_debug_sync_control
+{
+  st_debug_sync_action  *ds_action;             /* array of actions */
+  uint                  ds_active;              /* # active actions */
+  uint                  ds_allocated;           /* # allocated actions */
+  ulonglong             dsp_hits;               /* statistics */
+  ulonglong             dsp_executed;           /* statistics */
+  ulonglong             dsp_max_active;         /* statistics */
+  /*
+    thd->proc_info points at unsynchronized memory.
+    It must not go away as long as the thread exists.
+  */
+  char                  ds_proc_info[80];       /* proc_info string */
+};
+
+
+/**
+  Definitions for the debug sync facility.
+  1. Global string variable to hold a "signal" ("signal post", "flag mast").
+  2. Global condition variable for signaling and waiting.
+  3. Global mutex to synchronize access to the above.
+*/
+struct st_debug_sync_globals
+{
+  String                ds_signal;              /* signal variable */
+  pthread_cond_t        ds_cond;                /* condition variable */
+  pthread_mutex_t       ds_mutex;               /* mutex variable */
+  ulonglong             dsp_hits;               /* statistics */
+  ulonglong             dsp_executed;           /* statistics */
+  ulonglong             dsp_max_active;         /* statistics */
+};
+static st_debug_sync_globals debug_sync_global; /* All globals in one object */
+
+/**
+  Callback pointer for C files.
+*/
+extern "C" void (*debug_sync_C_callback_ptr)(const char *, size_t);
+
+
+/**
+  Callback for debug sync, to be used by C files. See thr_lock.c for example.
+
+  @description
+
+    We cannot place a sync point directly in C files (like those in mysys or
+    certain storage engines written mostly in C like MyISAM or Maria). Because
+    they are C code and do not include mysql_priv.h. So they do not know the
+    macro DEBUG_SYNC(thd, sync_point_name). The macro needs a 'thd' argument.
+    Hence it cannot be used in files outside of the sql/ directory.
+
+    The workaround is to call back simple functions like this one from
+    non-sql/ files.
+
+    We want to allow modules like thr_lock to be used without sql/ and
+    especially without Debug Sync. So we cannot just do a simple call
+    of the callback function. Instead we provide a global pointer in
+    the other file, which is to be set to the callback by Debug Sync.
+    If the pointer is not set, no call back will be done. If Debug
+    Sync sets the pointer to a callback function like this one, it will
+    be called. That way thr_lock.c does not have an undefined reference
+    to Debug Sync and can be used without it. Debug Sync, in contrast,
+    has an undefined reference to that pointer and thus requires
+    thr_lock to be linked too. But this is not a problem as it is part
+    of the MySQL server anyway.
+
+  @note
+    The callback pointer in C files is set only if debug sync is
+    initialized. And this is done only if opt_debug_sync_timeout is set.
+*/
+
+static void debug_sync_C_callback(const char *sync_point_name,
+                                  size_t name_len)
+{
+  if (unlikely(opt_debug_sync_timeout))                            
+    debug_sync(current_thd, sync_point_name, name_len);   
+}
+
+
+/**
+  Initialize the debug sync facility at server start.
+
+  @return status
+    @retval     0       ok
+    @retval     != 0    error
+*/
+
+int debug_sync_init(void)
+{
+  DBUG_ENTER("debug_sync_init");
+
+  if (opt_debug_sync_timeout)
+  {
+    int rc;
+
+    /* Initialize the global variables. */
+    debug_sync_global.ds_signal.length(0);
+    if ((rc= pthread_cond_init(&debug_sync_global.ds_cond, NULL)) ||
+        (rc= pthread_mutex_init(&debug_sync_global.ds_mutex,
+                                MY_MUTEX_INIT_FAST)))
+      DBUG_RETURN(rc); /* purecov: inspected */
+
+    /* Set the call back pointer in C files. */
+    debug_sync_C_callback_ptr= debug_sync_C_callback;
+  }
+
+  DBUG_RETURN(0);
+}
+
+
+/**
+  End the debug sync facility.
+
+  @description
+    This is called at server shutdown or after a thread initialization error.
+*/
+
+void debug_sync_end(void)
+{
+  DBUG_ENTER("debug_sync_end");
+
+  /* End the facility only if it had been initialized. */
+  if (debug_sync_C_callback_ptr)
+  {
+    /* Clear the call back pointer in C files. */
+    debug_sync_C_callback_ptr= NULL;
+
+    /* Destroy the global variables. */
+    debug_sync_global.ds_signal.free();
+    (void) pthread_cond_destroy(&debug_sync_global.ds_cond);
+    (void) pthread_mutex_destroy(&debug_sync_global.ds_mutex);
+
+    /* Print statistics. */
+    {
+      char llbuff[22];
+      sql_print_information("Debug sync points hit:                   %22s",
+                            llstr(debug_sync_global.dsp_hits, llbuff));
+      sql_print_information("Debug sync points executed:              %22s",
+                            llstr(debug_sync_global.dsp_executed, llbuff));
+      sql_print_information("Debug sync points max active per thread: %22s",
+                            llstr(debug_sync_global.dsp_max_active, llbuff));
+    }
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+
+/* purecov: begin tested */
+
+/**
+  Disable the facility after lack of memory if no error can be returned.
+
+  @note
+    Do not end the facility here because the global variables can
+    be in use by other threads.
+*/
+
+static void debug_sync_emergency_disable(void)
+{
+  DBUG_ENTER("debug_sync_emergency_disable");
+
+  opt_debug_sync_timeout= 0;
+
+  DBUG_PRINT("debug_sync",
+             ("Debug Sync Facility disabled due to lack of memory."));
+  sql_print_error("Debug Sync Facility disabled due to lack of memory.");
+
+  DBUG_VOID_RETURN;
+}
+
+/* purecov: end */
+
+
+/**
+  Initialize the debug sync facility at thread start.
+
+  @param[in]    thd             thread handle
+*/
+
+void debug_sync_init_thread(THD *thd)
+{
+  DBUG_ENTER("debug_sync_init_thread");
+  DBUG_ASSERT(thd);
+
+  if (opt_debug_sync_timeout)
+  {
+    thd->debug_sync_control= (st_debug_sync_control*)
+      my_malloc(sizeof(st_debug_sync_control), MYF(MY_WME | MY_ZEROFILL));
+    if (!thd->debug_sync_control)
+    {
+      /*
+        Error is reported by my_malloc().
+        We must disable the facility. We have no way to return an error.
+      */
+      debug_sync_emergency_disable(); /* purecov: tested */
+    }
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+
+/**
+  End the debug sync facility at thread end.
+
+  @param[in]    thd             thread handle
+*/
+
+void debug_sync_end_thread(THD *thd)
+{
+  DBUG_ENTER("debug_sync_end_thread");
+  DBUG_ASSERT(thd);
+
+  if (thd->debug_sync_control)
+  {
+    st_debug_sync_control *ds_control= thd->debug_sync_control;
+
+    /*
+      This synchronization point can be used to synchronize on thread end.
+      This is the latest point in a THD's life, where this can be done.
+    */
+    DEBUG_SYNC(thd, "thread_end");
+
+    if (ds_control->ds_action)
+    {
+      st_debug_sync_action *action= ds_control->ds_action;
+      st_debug_sync_action *action_end= action + ds_control->ds_allocated;
+      for (; action < action_end; action++)
+      {
+        action->signal.free();
+        action->wait_for.free();
+        action->sync_point.free();
+      }
+      my_free(ds_control->ds_action, MYF(0));
+    }
+
+    /* Statistics. */
+    pthread_mutex_lock(&debug_sync_global.ds_mutex);
+    debug_sync_global.dsp_hits+=           ds_control->dsp_hits;
+    debug_sync_global.dsp_executed+=       ds_control->dsp_executed;
+    if (debug_sync_global.dsp_max_active < ds_control->dsp_max_active)
+      debug_sync_global.dsp_max_active=    ds_control->dsp_max_active;
+    pthread_mutex_unlock(&debug_sync_global.ds_mutex);
+
+    my_free(ds_control, MYF(0));
+    thd->debug_sync_control= NULL;
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+
+/**
+  Move a string by length.
+
+  @param[out]   to              buffer for the resulting string
+  @param[in]    to_end          end of buffer
+  @param[in]    from            source string
+  @param[in]    length          number of bytes to copy
+
+  @return       pointer to end of copied string
+*/
+
+static char *debug_sync_bmove_len(char *to, char *to_end,
+                                  const char *from, size_t length)
+{
+  DBUG_ASSERT(to);
+  DBUG_ASSERT(to_end);
+  DBUG_ASSERT(!length || from);
+  set_if_smaller(length, (size_t) (to_end - to));
+  memcpy(to, from, length);
+  return (to + length);
+}
+
+
+#if !defined(DBUG_OFF)
+
+/**
+  Create a string that describes an action.
+
+  @param[out]   result          buffer for the resulting string
+  @param[in]    size            size of result buffer
+  @param[in]    action          action to describe
+*/
+
+static void debug_sync_action_string(char *result, uint size,
+                                     st_debug_sync_action *action)
+{
+  char  *wtxt= result;
+  char  *wend= wtxt + size - 1; /* Allow emergency '\0'. */
+  DBUG_ASSERT(result);
+  DBUG_ASSERT(action);
+
+  /* If an execute count is present, signal or wait_for are needed too. */
+  DBUG_ASSERT(!action->execute ||
+              action->signal.length() || action->wait_for.length());
+
+  if (action->execute)
+  {
+    if (action->signal.length())
+    {
+      wtxt= debug_sync_bmove_len(wtxt, wend, STRING_WITH_LEN("SIGNAL "));
+      wtxt= debug_sync_bmove_len(wtxt, wend, action->signal.ptr(),
+                                 action->signal.length());
+    }
+    if (action->wait_for.length())
+    {
+      if ((wtxt == result) && (wtxt < wend))
+        *(wtxt++)= ' ';
+      wtxt= debug_sync_bmove_len(wtxt, wend, STRING_WITH_LEN(" WAIT_FOR "));
+      wtxt= debug_sync_bmove_len(wtxt, wend, action->wait_for.ptr(),
+                                 action->wait_for.length());
+
+      if (action->timeout != opt_debug_sync_timeout)
+      {
+        wtxt+= my_snprintf(wtxt, wend - wtxt, " TIMEOUT %lu", action->timeout);
+      }
+    }
+    if (action->execute != 1)
+    {
+      wtxt+= my_snprintf(wtxt, wend - wtxt, " EXECUTE %lu", action->execute);
+    }
+  }
+  if (action->hit_limit)
+  {
+    wtxt+= my_snprintf(wtxt, wend - wtxt, "%sHIT_LIMIT %lu",
+                       (wtxt == result) ? "" : " ", action->hit_limit);
+  }
+
+  /*
+    If (wtxt == wend) string may not be terminated.
+    There is one byte left for an emergency termination.
+  */
+  *wtxt= '\0';
+}
+
+
+/**
+  Print actions.
+
+  @param[in]    thd             thread handle
+*/
+
+static void debug_sync_print_actions(THD *thd)
+{
+  st_debug_sync_control *ds_control= thd->debug_sync_control;
+  uint                  idx;
+  DBUG_ENTER("debug_sync_print_actions");
+  DBUG_ASSERT(thd);
+
+  if (!ds_control)
+    DBUG_VOID_RETURN;
+
+  for (idx= 0; idx < ds_control->ds_active; idx++)
+  {
+    const char *dsp_name= ds_control->ds_action[idx].sync_point.c_ptr();
+    char action_string[256];
+
+    debug_sync_action_string(action_string, sizeof(action_string),
+                             ds_control->ds_action + idx);
+    DBUG_PRINT("debug_sync_list", ("%s %s", dsp_name, action_string));
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+#endif /* !defined(DBUG_OFF) */
+
+
+/**
+  Compare two actions by sync point name length, string.
+
+  @param[in]    arg1            reference to action1
+  @param[in]    arg2            reference to action2
+
+  @return       difference
+    @retval     == 0            length1/string1 is same as length2/string2
+    @retval     < 0             length1/string1 is smaller
+    @retval     > 0             length1/string1 is bigger
+*/
+
+static int debug_sync_qsort_cmp(const void* arg1, const void* arg2)
+{
+  st_debug_sync_action *action1= (st_debug_sync_action*) arg1;
+  st_debug_sync_action *action2= (st_debug_sync_action*) arg2;
+  int diff;
+  DBUG_ASSERT(action1);
+  DBUG_ASSERT(action2);
+
+  if (!(diff= action1->sync_point.length() - action2->sync_point.length()))
+    diff= memcmp(action1->sync_point.ptr(), action2->sync_point.ptr(),
+                 action1->sync_point.length());
+
+  return diff;
+}
+
+
+/**
+  Find a debug sync action.
+
+  @param[in]    actionarr       array of debug sync actions
+  @param[in]    quantity        number of actions in array
+  @param[in]    dsp_name        name of debug sync point to find
+  @param[in]    name_len        length of name of debug sync point
+
+  @return       action
+    @retval     != NULL         found sync point in array
+    @retval     NULL            not found
+
+  @description
+    Binary search. Array needs to be sorted by length, sync point name.
+*/
+
+static st_debug_sync_action *debug_sync_find(st_debug_sync_action *actionarr,
+                                             int quantity,
+                                             const char *dsp_name,
+                                             uint name_len)
+{
+  st_debug_sync_action  *action;
+  int                   low ;
+  int                   high ;
+  int                   mid ;
+  int                   diff ;
+  DBUG_ASSERT(actionarr);
+  DBUG_ASSERT(dsp_name);
+  DBUG_ASSERT(name_len);
+
+  low= 0;
+  high= quantity;
+
+  while (low < high)
+  {
+    mid= (low + high) / 2;
+    action= actionarr + mid;
+    if (!(diff= name_len - action->sync_point.length()) &&
+        !(diff= memcmp(dsp_name, action->sync_point.ptr(), name_len)))
+      return action;
+    if (diff > 0)
+      low= mid + 1;
+    else
+      high= mid - 1;
+  }
+
+  if (low < quantity)
+  {
+    action= actionarr + low;
+    if ((name_len == action->sync_point.length()) &&
+        !memcmp(dsp_name, action->sync_point.ptr(), name_len))
+      return action;
+  }
+
+  return NULL;
+}
+
+
+/**
+  Reset the debug sync facility.
+
+  @param[in]    thd             thread handle
+
+  @description
+    Remove all actions of this thread.
+    Clear the global signal.
+*/
+
+static void debug_sync_reset(THD *thd)
+{
+  st_debug_sync_control *ds_control= thd->debug_sync_control;
+  DBUG_ENTER("debug_sync_reset");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(ds_control);
+
+  /* Remove all actions of this thread. */
+  ds_control->ds_active= 0;
+
+  /* Clear the global signal. */
+  pthread_mutex_lock(&debug_sync_global.ds_mutex);
+  debug_sync_global.ds_signal.length(0);
+  pthread_mutex_unlock(&debug_sync_global.ds_mutex);
+
+  DBUG_VOID_RETURN;
+}
+
+
+/**
+  Remove a debug sync action.
+
+  @param[in]    ds_control      control object
+  @param[in]    action          action to be removed
+
+  @description
+    Removing an action mainly means to decrement the ds_active counter.
+    But if the action is between other active action in the array, then
+    the array needs to be shrinked. The active actions above the one to
+    be removed have to be moved down by one slot.
+*/
+
+static void debug_sync_remove_action(st_debug_sync_control *ds_control,
+                                     st_debug_sync_action *action)
+{
+  uint dsp_idx= action - ds_control->ds_action;
+  DBUG_ENTER("debug_sync_remove_action");
+  DBUG_ASSERT(ds_control);
+  DBUG_ASSERT(ds_control == current_thd->debug_sync_control);
+  DBUG_ASSERT(action);
+  DBUG_ASSERT(dsp_idx < ds_control->ds_active);
+
+  /* Decrement the number of currently active actions. */
+  ds_control->ds_active--;
+
+  /*
+    If this was not the last active action in the array, we need to
+    shift remaining active actions down to keep the array gap-free.
+    Otherwise binary search might fail or take longer than necessary at
+    least. Also new actions are always put to the end of the array.
+  */
+  if (ds_control->ds_active > dsp_idx)
+  {
+    /*
+      Do not make save_action an object of class st_debug_sync_action.
+      Its destructor would tamper with the String pointers.
+    */
+    uchar save_action[sizeof(st_debug_sync_action)];
+
+    /*
+      Copy the to-be-removed action object to temporary storage before
+      the shift copies the string pointers over. Do not use assignment
+      because it would use assignment operator methods for the Strings.
+      This would copy the strings. The shift below overwrite the string
+      pointers without freeing them first. By using memmove() we save
+      the pointers, which are overwritten by the shift.
+    */
+    memmove(save_action, action, sizeof(st_debug_sync_action));
+
+    /* Move actions down. */
+    memmove(ds_control->ds_action + dsp_idx,
+            ds_control->ds_action + dsp_idx + 1,
+            (ds_control->ds_active - dsp_idx) *
+            sizeof(st_debug_sync_action));
+
+    /*
+      Copy back the saved action object to the now free array slot. This
+      replaces the double references of String pointers that have been
+      produced by the shift. Again do not use an assignment operator to
+      avoid string allocation/copy.
+    */
+    memmove(ds_control->ds_action + ds_control->ds_active, save_action,
+            sizeof(st_debug_sync_action));
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+
+/**
+  Get a debug sync action.
+
+  @param[in]    thd             thread handle
+  @param[in]    dsp_name        debug sync point name
+  @param[in]    name_len        length of sync point name
+
+  @return       action
+    @retval     != NULL         ok
+    @retval     NULL            error
+
+  @description
+    Find the debug sync action for a debug sync point or make a new one.
+*/
+
+static st_debug_sync_action *debug_sync_get_action(THD *thd,
+                                                   const char *dsp_name,
+                                                   uint name_len)
+{
+  st_debug_sync_control *ds_control= thd->debug_sync_control;
+  st_debug_sync_action  *action;
+  DBUG_ENTER("debug_sync_get_action");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(dsp_name);
+  DBUG_ASSERT(name_len);
+  DBUG_ASSERT(ds_control);
+  DBUG_PRINT("debug_sync", ("sync_point: '%.*s'", (int) name_len, dsp_name));
+  DBUG_PRINT("debug_sync", ("active: %u  allocated: %u",
+                            ds_control->ds_active, ds_control->ds_allocated));
+
+  /* There cannot be more active actions than allocated. */
+  DBUG_ASSERT(ds_control->ds_active <= ds_control->ds_allocated);
+  /* If there are active actions, the action array must be present. */
+  DBUG_ASSERT(!ds_control->ds_active || ds_control->ds_action);
+
+  /* Try to reuse existing action if there is one for this sync point. */
+  if (ds_control->ds_active &&
+      (action= debug_sync_find(ds_control->ds_action, ds_control->ds_active,
+                               dsp_name, name_len)))
+  {
+    /* Reuse an already active sync point action. */
+    DBUG_ASSERT((uint)(action - ds_control->ds_action) < ds_control->ds_active);
+    DBUG_PRINT("debug_sync", ("reuse action idx: %ld",
+                              (long) (action - ds_control->ds_action)));
+  }
+  else
+  {
+    /* Create a new action. */
+    int dsp_idx= ds_control->ds_active++;
+    set_if_bigger(ds_control->dsp_max_active, ds_control->ds_active);
+    if (ds_control->ds_active > ds_control->ds_allocated)
+    {
+      uint new_alloc= ds_control->ds_active + 3;
+      void *new_action= my_realloc(ds_control->ds_action,
+                                   new_alloc * sizeof(st_debug_sync_action),
+                                   MYF(MY_WME | MY_ALLOW_ZERO_PTR));
+      if (!new_action)
+      {
+        /* Error is reported by my_malloc(). */
+        goto err; /* purecov: tested */
+      }
+      ds_control->ds_action= (st_debug_sync_action*) new_action;
+      ds_control->ds_allocated= new_alloc;
+      /* Clear memory as we do not run string constructors here. */
+      bzero((uchar*) (ds_control->ds_action + dsp_idx),
+            (new_alloc - dsp_idx) * sizeof(st_debug_sync_action));
+    }
+    DBUG_PRINT("debug_sync", ("added action idx: %u", dsp_idx));
+    action= ds_control->ds_action + dsp_idx;
+    if (action->sync_point.copy(dsp_name, name_len, system_charset_info))
+    {
+      /* Error is reported by my_malloc(). */
+      goto err; /* purecov: tested */
+    }
+    action->need_sort= TRUE;
+  }
+  DBUG_ASSERT(action >= ds_control->ds_action);
+  DBUG_ASSERT(action < ds_control->ds_action + ds_control->ds_active);
+  DBUG_PRINT("debug_sync", ("action: 0x%lx  array: 0x%lx  count: %u",
+                            (long) action, (long) ds_control->ds_action,
+                            ds_control->ds_active));
+
+  DBUG_RETURN(action);
+
+  /* purecov: begin tested */
+ err:
+  DBUG_RETURN(NULL);
+  /* purecov: end */
+}
+
+
+/**
+  Set a debug sync action.
+
+  @param[in]    thd             thread handle
+  @param[in]    action          synchronization action
+
+  @return       status
+    @retval     FALSE           ok
+    @retval     TRUE            error
+
+  @description
+    This is called from the debug sync parser. It arms the action for
+    the requested sync point. If the action parsed into an empty action,
+    it is removed instead.
+
+    Setting an action for a sync point means to make the sync point
+    active. When it is hit it will execute this action.
+
+    Before parsing, we "get" an action object. This is placed at the
+    end of the thread's action array unless the requested sync point
+    has an action already.
+
+    Then the parser fills the action object from the request string.
+
+    Finally the action is "set" for the sync point. If it was parsed
+    to be empty, it is removed from the array. If it did belong to a
+    sync point before, the sync point becomes inactive. If the action
+    became non-empty and it did not belong to a sync point before (it
+    was added at the end of the action array), the action array needs
+    to be sorted by sync point.
+
+    If the sync point name is "now", it is executed immediately.
+*/
+
+static bool debug_sync_set_action(THD *thd, st_debug_sync_action *action)
+{
+  st_debug_sync_control *ds_control= thd->debug_sync_control;
+  bool is_dsp_now= FALSE;
+  DBUG_ENTER("debug_sync_set_action");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(action);
+  DBUG_ASSERT(ds_control);
+
+  action->activation_count= max(action->hit_limit, action->execute);
+  if (!action->activation_count)
+  {
+    debug_sync_remove_action(ds_control, action);
+    DBUG_PRINT("debug_sync", ("action cleared"));
+  }
+  else
+  {
+    const char *dsp_name= action->sync_point.c_ptr();
+    DBUG_EXECUTE("debug_sync", {
+        /* Functions as DBUG_PRINT args can change keyword and line nr. */
+        const char *sig_emit= action->signal.c_ptr();
+        const char *sig_wait= action->wait_for.c_ptr();
+        DBUG_PRINT("debug_sync",
+                   ("sync_point: '%s'  activation_count: %lu  hit_limit: %lu  "
+                    "execute: %lu  timeout: %lu  signal: '%s'  wait_for: '%s'",
+                    dsp_name, action->activation_count,
+                    action->hit_limit, action->execute, action->timeout,
+                    sig_emit, sig_wait));});
+
+    /* Check this before sorting the array. action may move. */
+    is_dsp_now= !my_strcasecmp(system_charset_info, dsp_name, "now");
+
+    if (action->need_sort)
+    {
+      action->need_sort= FALSE;
+      /* Sort actions by (name_len, name). */
+      my_qsort(ds_control->ds_action, ds_control->ds_active,
+               sizeof(st_debug_sync_action), debug_sync_qsort_cmp);
+    }
+  }
+  DBUG_EXECUTE("debug_sync_list", debug_sync_print_actions(thd););
+
+  /* Execute the special sync point 'now' if activated above. */
+  if (is_dsp_now)
+  {
+    DEBUG_SYNC(thd, "now");
+    /*
+      If HIT_LIMIT for sync point "now" was 1, the execution of the sync
+      point decremented it to 0. In this case the following happened:
+
+      - an error message was reported with my_error() and
+      - the statement was killed with thd->killed= THD::KILL_QUERY.
+
+      If a statement reports an error, it must not call send_ok().
+      The calling functions will not call send_ok(), if we return TRUE
+      from this function.
+
+      thd->killed is also set if the wait is interrupted from a
+      KILL or KILL QUERY statement. In this case, no error is reported
+      and shall not be reported as a result of SET DEBUG_SYNC.
+      Hence, we check for the first condition above.
+    */
+    if (thd->is_error())
+      DBUG_RETURN(TRUE);
+  }
+
+  DBUG_RETURN(FALSE);
+}
+
+
+/**
+  Extract a token from a string.
+
+  @param[out]     token_p         returns start of token
+  @param[out]     token_length_p  returns length of token
+  @param[in,out]  ptr             current string pointer, adds '\0' terminators
+
+  @return       string pointer or NULL
+    @retval     != NULL         ptr behind token terminator or at string end
+    @retval     NULL            no token found in remainder of string
+
+  @note
+    This function assumes that the string is in system_charset_info,
+    that this charset is single byte for ASCII NUL ('\0'), that no
+    character except of ASCII NUL ('\0') contains a byte with value 0,
+    and that ASCII NUL ('\0') is used as the string terminator.
+
+    This function needs to return tokens that are terminated with ASCII
+    NUL ('\0'). The tokens are used in my_strcasecmp(). Unfortunately
+    there is no my_strncasecmp().
+
+    To return the last token without copying it, we require the input
+    string to be nul terminated.
+
+  @description
+    This function skips space characters at string begin.
+
+    It returns a pointer to the first non-space character in *token_p.
+
+    If no non-space character is found before the string terminator
+    ASCII NUL ('\0'), the function returns NULL. *token_p and
+    *token_length_p remain unchanged in this case (they are not set).
+
+    The function takes a space character or an ASCII NUL ('\0') as a
+    terminator of the token. The space character could be multi-byte.
+
+    It returns the length of the token in bytes, excluding the
+    terminator, in *token_length_p.
+
+    If the terminator of the token is ASCII NUL ('\0'), it returns a
+    pointer to the terminator (string end).
+
+    If the terminator is a space character, it replaces the the first
+    byte of the terminator character by ASCII NUL ('\0'), skips the (now
+    corrupted) terminator character, and skips all following space
+    characters. It returns a pointer to the next non-space character or
+    to the string terminator ASCII NUL ('\0').
+*/
+
+static char *debug_sync_token(char **token_p, uint *token_length_p, char *ptr)
+{
+  DBUG_ASSERT(token_p);
+  DBUG_ASSERT(token_length_p);
+  DBUG_ASSERT(ptr);
+
+  /* Skip leading space */
+  while (my_isspace(system_charset_info, *ptr))
+    ptr+= my_mbcharlen(system_charset_info, (uchar) *ptr);
+
+  if (!*ptr)
+  {
+    ptr= NULL;
+    goto end;
+  }
+
+  /* Get token start. */
+  *token_p= ptr;
+
+  /* Find token end. */
+  while (*ptr && !my_isspace(system_charset_info, *ptr))
+    ptr+= my_mbcharlen(system_charset_info, (uchar) *ptr);
+
+  /* Get token length. */
+  *token_length_p= ptr - *token_p;
+
+  /* If necessary, terminate token. */
+  if (*ptr)
+  {
+    /* Get terminator character length. */
+    uint mbspacelen= my_mbcharlen(system_charset_info, (uchar) *ptr);
+
+    /* Terminate token. */
+    *ptr= '\0';
+
+    /* Skip the terminator. */
+    ptr+= mbspacelen;
+
+    /* Skip trailing space */
+    while (my_isspace(system_charset_info, *ptr))
+      ptr+= my_mbcharlen(system_charset_info, (uchar) *ptr);
+  }
+
+ end:
+  return ptr;
+}
+
+
+/**
+  Extract a number from a string.
+
+  @param[out]   number_p        returns number
+  @param[in]    actstrptr       current pointer in action string
+
+  @return       string pointer or NULL
+    @retval     != NULL         ptr behind token terminator or at string end
+    @retval     NULL            no token found or token is not valid number
+
+  @note
+    The same assumptions about charset apply as for debug_sync_token().
+
+  @description
+    This function fetches a token from the string and converts it
+    into a number.
+
+    If there is no token left in the string, or the token is not a valid
+    decimal number, NULL is returned. The result in *number_p is
+    undefined in this case.
+*/
+
+static char *debug_sync_number(ulong *number_p, char *actstrptr)
+{
+  char                  *ptr;
+  char                  *ept;
+  char                  *token;
+  uint                  token_length;
+  DBUG_ASSERT(number_p);
+  DBUG_ASSERT(actstrptr);
+
+  /* Get token from string. */
+  if (!(ptr= debug_sync_token(&token, &token_length, actstrptr)))
+    goto end;
+
+  *number_p= strtoul(token, &ept, 10);
+  if (*ept)
+    ptr= NULL;
+
+ end:
+  return ptr;
+}
+
+
+/**
+  Evaluate a debug sync action string.
+
+  @param[in]        thd             thread handle
+  @param[in,out]    action_str      action string to receive '\0' terminators
+
+  @return           status
+    @retval         FALSE           ok
+    @retval         TRUE            error
+
+  @description
+    This is called when the DEBUG_SYNC system variable is set.
+    Parse action string, build a debug sync action, activate it.
+
+    Before parsing, we "get" an action object. This is placed at the
+    end of the thread's action array unless the requested sync point
+    has an action already.
+
+    Then the parser fills the action object from the request string.
+
+    Finally the action is "set" for the sync point. This means that the
+    sync point becomes active or inactive, depending on the action
+    values.
+
+  @note
+    The input string needs to be ASCII NUL ('\0') terminated. We split
+    nul-terminated tokens in it without copy.
+
+  @see the function comment of debug_sync_token() for more constraints
+    for the string.
+*/
+
+static bool debug_sync_eval_action(THD *thd, char *action_str)
+{
+  st_debug_sync_action  *action= NULL;
+  const char            *errmsg;
+  char                  *ptr;
+  char                  *token;
+  uint                  token_length;
+  DBUG_ENTER("debug_sync_eval_action");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(action_str);
+
+  /*
+    Get debug sync point name. Or a special command.
+  */
+  if (!(ptr= debug_sync_token(&token, &token_length, action_str)))
+  {
+    errmsg= "Missing synchronization point name";
+    goto err;
+  }
+
+  /*
+    If there is a second token, the first one is the sync point name.
+  */
+  if (*ptr)
+  {
+    /* Get an action object to collect the requested action parameters. */
+    action= debug_sync_get_action(thd, token, token_length);
+    if (!action)
+    {
+      /* Error message is sent. */
+      DBUG_RETURN(TRUE); /* purecov: tested */
+    }
+  }
+
+  /*
+    Get kind of action to be taken at sync point.
+  */
+  if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+  {
+    /* No action present. Try special commands. Token unchanged. */
+
+    /*
+      Try RESET.
+    */
+    if (!my_strcasecmp(system_charset_info, token, "RESET"))
+    {
+      /* It is RESET. Reset all actions and global signal. */
+      debug_sync_reset(thd);
+      goto end;
+    }
+
+    /* Token unchanged. It still contains sync point name. */
+    errmsg= "Missing action after synchronization point name '%.*s'";
+    goto err;
+  }
+
+  /*
+    Check for pseudo actions first. Start with actions that work on
+    an existing action.
+  */
+  DBUG_ASSERT(action);
+
+  /*
+    Try TEST.
+  */
+  if (!my_strcasecmp(system_charset_info, token, "TEST"))
+  {
+    /* It is TEST. Nothing must follow it. */
+    if (*ptr)
+    {
+      errmsg= "Nothing must follow action TEST";
+      goto err;
+    }
+
+    /* Execute sync point. */
+    debug_sync(thd, action->sync_point.ptr(), action->sync_point.length());
+    /* Fix statistics. This was not a real hit of the sync point. */
+    thd->debug_sync_control->dsp_hits--;
+    goto end;
+  }
+
+  /*
+    Now check for actions that define a new action.
+    Initialize action. Do not use bzero(). Strings may have malloced.
+  */
+  action->activation_count= 0;
+  action->hit_limit= 0;
+  action->execute= 0;
+  action->timeout= 0;
+  action->signal.length(0);
+  action->wait_for.length(0);
+
+  /*
+    Try CLEAR.
+  */
+  if (!my_strcasecmp(system_charset_info, token, "CLEAR"))
+  {
+    /* It is CLEAR. Nothing must follow it. */
+    if (*ptr)
+    {
+      errmsg= "Nothing must follow action CLEAR";
+      goto err;
+    }
+
+    /* Set (clear/remove) action. */
+    goto set_action;
+  }
+
+  /*
+    Now check for real sync point actions.
+  */
+
+  /*
+    Try SIGNAL.
+  */
+  if (!my_strcasecmp(system_charset_info, token, "SIGNAL"))
+  {
+    /* It is SIGNAL. Signal name must follow. */
+    if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+    {
+      errmsg= "Missing signal name after action SIGNAL";
+      goto err;
+    }
+    if (action->signal.copy(token, token_length, system_charset_info))
+    {
+      /* Error is reported by my_malloc(). */
+      /* purecov: begin tested */
+      errmsg= NULL;
+      goto err;
+      /* purecov: end */
+    }
+
+    /* Set default for EXECUTE option. */
+    action->execute= 1;
+
+    /* Get next token. If none follows, set action. */
+    if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+      goto set_action;
+  }
+
+  /*
+    Try WAIT_FOR.
+  */
+  if (!my_strcasecmp(system_charset_info, token, "WAIT_FOR"))
+  {
+    /* It is WAIT_FOR. Wait_for signal name must follow. */
+    if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+    {
+      errmsg= "Missing signal name after action WAIT_FOR";
+      goto err;
+    }
+    if (action->wait_for.copy(token, token_length, system_charset_info))
+    {
+      /* Error is reported by my_malloc(). */
+      /* purecov: begin tested */
+      errmsg= NULL;
+      goto err;
+      /* purecov: end */
+    }
+
+    /* Set default for EXECUTE and TIMEOUT options. */
+    action->execute= 1;
+    action->timeout= opt_debug_sync_timeout;
+
+    /* Get next token. If none follows, set action. */
+    if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+      goto set_action;
+
+    /*
+      Try TIMEOUT.
+    */
+    if (!my_strcasecmp(system_charset_info, token, "TIMEOUT"))
+    {
+      /* It is TIMEOUT. Number must follow. */
+      if (!(ptr= debug_sync_number(&action->timeout, ptr)))
+      {
+        errmsg= "Missing valid number after TIMEOUT";
+        goto err;
+      }
+
+      /* Get next token. If none follows, set action. */
+      if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+        goto set_action;
+    }
+  }
+
+  /*
+    Try EXECUTE.
+  */
+  if (!my_strcasecmp(system_charset_info, token, "EXECUTE"))
+  {
+    /*
+      EXECUTE requires either SIGNAL and/or WAIT_FOR to be present.
+      In this case action->execute has been preset to 1.
+    */
+    if (!action->execute)
+    {
+      errmsg= "Missing action before EXECUTE";
+      goto err;
+    }
+
+    /* Number must follow. */
+    if (!(ptr= debug_sync_number(&action->execute, ptr)))
+    {
+      errmsg= "Missing valid number after EXECUTE";
+      goto err;
+    }
+
+    /* Get next token. If none follows, set action. */
+    if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+      goto set_action;
+  }
+
+  /*
+    Try HIT_LIMIT.
+  */
+  if (!my_strcasecmp(system_charset_info, token, "HIT_LIMIT"))
+  {
+    /* Number must follow. */
+    if (!(ptr= debug_sync_number(&action->hit_limit, ptr)))
+    {
+      errmsg= "Missing valid number after HIT_LIMIT";
+      goto err;
+    }
+
+    /* Get next token. If none follows, set action. */
+    if (!(ptr= debug_sync_token(&token, &token_length, ptr)))
+      goto set_action;
+  }
+
+  errmsg= "Illegal or out of order stuff: '%.*s'";
+
+ err:
+  if (errmsg)
+  {
+    /*
+      NOTE: errmsg must either have %.*s or none % at all.
+      It can be NULL if an error message is already reported
+      (e.g. by my_malloc()).
+    */
+    set_if_smaller(token_length, 64); /* Limit error message length. */
+    my_printf_error(ER_PARSE_ERROR, errmsg, MYF(0), token_length, token);
+  }
+  if (action)
+    debug_sync_remove_action(thd->debug_sync_control, action);
+  DBUG_RETURN(TRUE);
+
+ set_action:
+  DBUG_RETURN(debug_sync_set_action(thd, action));
+
+ end:
+  DBUG_RETURN(FALSE);
+}
+
+
+/**
+  Check if the system variable 'debug_sync' can be set.
+
+  @param[in]    thd             thread handle
+  @param[in]    var             set variable request
+
+  @return       status
+    @retval     FALSE           ok, variable can be set
+    @retval     TRUE            error, variable cannot be set
+*/
+
+bool sys_var_debug_sync::check(THD *thd, set_var *var)
+{
+  DBUG_ENTER("sys_var_debug_sync::check");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(var);
+
+  /*
+    Variable can be set for the session only.
+
+    This could be changed later. Then we need to have a global array of
+    actions in addition to the thread local ones. SET GLOBAL would
+    manage the global array, SET [SESSION] the local array. A sync point
+    would need to look for a local and a global action. Setting and
+    executing of global actions need to be protected by a mutex.
+
+    The purpose of global actions could be to allow synchronizing with
+    connectionless threads that cannot execute SET statements.
+  */
+  if (var->type == OPT_GLOBAL)
+  {
+    my_error(ER_LOCAL_VARIABLE, MYF(0), name);
+    DBUG_RETURN(TRUE);
+  }
+
+  /*
+    Do not check for disabled facility. Test result should not
+    unnecessarily differ from enabled facility.
+  */
+
+  /*
+    Facility requires SUPER privilege. Sync points could be inside
+    global mutexes (e.g. LOCK_open). Waiting there forever would
+    stall the whole server.
+  */
+  DBUG_RETURN(check_global_access(thd, SUPER_ACL));
+}
+
+
+/**
+  Set the system variable 'debug_sync'.
+
+  @param[in]    thd             thread handle
+  @param[in]    var             set variable request
+
+  @return       status
+    @retval     FALSE           ok, variable is set
+    @retval     TRUE            error, variable could not be set
+
+  @note
+    "Setting" of the system variable 'debug_sync' does not mean to
+    assign a value to it as usual. Instead a debug sync action is parsed
+    from the input string and stored apart from the variable value.
+
+  @note
+    For efficiency reasons, the action string parser places '\0'
+    terminators in the string. So we need to take a copy here.
+*/
+
+bool sys_var_debug_sync::update(THD *thd, set_var *var)
+{
+  char   *val_str;
+  String *val_ptr;
+  String val_buf;
+  DBUG_ENTER("sys_var_debug_sync::update");
+  DBUG_ASSERT(thd);
+
+  /*
+    Depending on the value type (string literal, user variable, ...)
+    val_buf receives a copy of the value or not. But we always need
+    a copy. So we take a copy, if it is not done by val_str().
+    If val_str() puts a copy into val_buf, then it returns &val_buf,
+    otherwise it returns a pointer to the string object that we need
+    to copy.
+  */
+  val_ptr= var ? var->value->val_str(&val_buf) : &val_buf;
+  if (val_ptr != &val_buf)
+  {
+    val_buf.copy(*val_ptr);
+  }
+  val_str= val_buf.c_ptr();
+  DBUG_PRINT("debug_sync", ("set action: '%s'", val_str));
+
+  /*
+    debug_sync_eval_action() places '\0' in the string, which itself
+    must be '\0' terminated.
+  */
+  DBUG_RETURN(opt_debug_sync_timeout ?
+              debug_sync_eval_action(thd, val_str) :
+              FALSE);
+}
+
+
+/**
+  Retrieve the value of the system variable 'debug_sync'.
+
+  @param[in]    thd             thread handle
+  @param[in]    type            variable type, unused
+  @param[in]    base            variable base, unused
+
+  @return       string
+    @retval     != NULL         ok, string pointer
+    @retval     NULL            memory allocation error
+
+  @note
+    The value of the system variable 'debug_sync' reflects if
+    the facility is enabled ("ON") or disabled (default, "OFF").
+
+    When "ON", the current signal is added.
+*/
+
+uchar *sys_var_debug_sync::value_ptr(THD *thd,
+                                     enum_var_type type __attribute__((unused)),
+                                     LEX_STRING *base __attribute__((unused)))
+{
+  char *value;
+  DBUG_ENTER("sys_var_debug_sync::value_ptr");
+  DBUG_ASSERT(thd);
+
+  if (opt_debug_sync_timeout)
+  {
+    static char on[]= "ON - current signal: '"; 
+
+    // Ensure exclusive access to debug_sync_global.ds_signal
+    pthread_mutex_lock(&debug_sync_global.ds_mutex);
+
+    size_t lgt= (sizeof(on) /* includes '\0' */ +
+                 debug_sync_global.ds_signal.length() + 1 /* for '\'' */);
+    char *vend;
+    char *vptr;
+
+    if ((value= (char*) alloc_root(thd->mem_root, lgt)))
+    {
+      vend= value + lgt - 1; /* reserve space for '\0'. */
+      vptr= debug_sync_bmove_len(value, vend, STRING_WITH_LEN(on));
+      vptr= debug_sync_bmove_len(vptr, vend, debug_sync_global.ds_signal.ptr(),
+                                 debug_sync_global.ds_signal.length());
+      if (vptr < vend)
+        *(vptr++)= '\'';
+      *vptr= '\0'; /* We have one byte reserved for the worst case. */
+    }
+    pthread_mutex_unlock(&debug_sync_global.ds_mutex);
+  }
+  else
+  {
+    /* purecov: begin tested */
+    value= strmake_root(thd->mem_root, STRING_WITH_LEN("OFF"));
+    /* purecov: end */
+  }
+
+  DBUG_RETURN((uchar*) value);
+}
+
+
+/**
+  Execute requested action at a synchronization point.
+
+  @param[in]    thd                 thread handle
+  @param[in]    action              action to be executed
+
+  @note
+    This is to be called only if activation count > 0.
+*/
+
+static void debug_sync_execute(THD *thd, st_debug_sync_action *action)
+{
+  IF_DBUG(const char *dsp_name= action->sync_point.c_ptr());
+  IF_DBUG(const char *sig_emit= action->signal.c_ptr());
+  IF_DBUG(const char *sig_wait= action->wait_for.c_ptr());
+  DBUG_ENTER("debug_sync_execute");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(action);
+  DBUG_PRINT("debug_sync",
+             ("sync_point: '%s'  activation_count: %lu  hit_limit: %lu  "
+              "execute: %lu  timeout: %lu  signal: '%s'  wait_for: '%s'",
+              dsp_name, action->activation_count, action->hit_limit,
+              action->execute, action->timeout, sig_emit, sig_wait));
+
+  DBUG_ASSERT(action->activation_count);
+  action->activation_count--;
+
+  if (action->execute)
+  {
+    const char  *old_proc_info;
+
+    action->execute--;
+
+    /*
+      If we will be going to wait, set proc_info for the PROCESSLIST table.
+      Do this before emitting the signal, so other threads can see it
+      if they awake before we enter_cond() below.
+    */
+    if (action->wait_for.length())
+    {
+      st_debug_sync_control *ds_control= thd->debug_sync_control;
+      strxnmov(ds_control->ds_proc_info, sizeof(ds_control->ds_proc_info)-1,
+               "debug sync point: ", action->sync_point.c_ptr(), NullS);
+      old_proc_info= thd->proc_info;
+      thd_proc_info(thd, ds_control->ds_proc_info);
+    }
+
+    /*
+      Take mutex to ensure that only one thread access
+      debug_sync_global.ds_signal at a time.  Need to take mutex for
+      read access too, to create a memory barrier in order to avoid that
+      threads just reads an old cached version of the signal.
+    */
+    pthread_mutex_lock(&debug_sync_global.ds_mutex);
+
+    if (action->signal.length())
+    {
+      /* Copy the signal to the global variable. */
+      if (debug_sync_global.ds_signal.copy(action->signal))
+      {
+        /*
+          Error is reported by my_malloc().
+          We must disable the facility. We have no way to return an error.
+        */
+        debug_sync_emergency_disable(); /* purecov: tested */
+      }
+      /* Wake threads waiting in a sync point. */
+      pthread_cond_broadcast(&debug_sync_global.ds_cond);
+      DBUG_PRINT("debug_sync_exec", ("signal '%s'  at: '%s'",
+                                     sig_emit, dsp_name));
+    } /* end if (action->signal.length()) */
+
+    if (action->wait_for.length())
+    {
+      pthread_mutex_t *old_mutex;
+      pthread_cond_t  *old_cond;
+      int             error= 0;
+      struct timespec abstime;
+
+      /*
+        We don't use enter_cond()/exit_cond(). They do not save old
+        mutex and cond. This would prohibit the use of DEBUG_SYNC
+        between other places of enter_cond() and exit_cond().
+      */
+      old_mutex= thd->mysys_var->current_mutex;
+      old_cond= thd->mysys_var->current_cond;
+      thd->mysys_var->current_mutex= &debug_sync_global.ds_mutex;
+      thd->mysys_var->current_cond= &debug_sync_global.ds_cond;
+
+      set_timespec(abstime, action->timeout);
+      DBUG_EXECUTE("debug_sync_exec", {
+          /* Functions as DBUG_PRINT args can change keyword and line nr. */
+          const char *sig_glob= debug_sync_global.ds_signal.c_ptr();
+          DBUG_PRINT("debug_sync_exec",
+                     ("wait for '%s'  at: '%s'  curr: '%s'",
+                      sig_wait, dsp_name, sig_glob));});
+
+      /*
+        Wait until global signal string matches the wait_for string.
+        Interrupt when thread or query is killed or facility disabled.
+        The facility can become disabled when some thread cannot get
+        the required dynamic memory allocated.
+      */
+      while (stringcmp(&debug_sync_global.ds_signal, &action->wait_for) &&
+             !thd->killed && opt_debug_sync_timeout)
+      {
+        error= pthread_cond_timedwait(&debug_sync_global.ds_cond,
+                                      &debug_sync_global.ds_mutex,
+                                      &abstime);
+        DBUG_EXECUTE("debug_sync", {
+            /* Functions as DBUG_PRINT args can change keyword and line nr. */
+            const char *sig_glob= debug_sync_global.ds_signal.c_ptr();
+            DBUG_PRINT("debug_sync",
+                       ("awoke from %s  global: %s  error: %d",
+                        sig_wait, sig_glob, error));});
+        if (error == ETIMEDOUT || error == ETIME)
+        {
+          push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
+                       ER_DEBUG_SYNC_TIMEOUT, ER(ER_DEBUG_SYNC_TIMEOUT));
+          break;
+        }
+        error= 0;
+      }
+      DBUG_EXECUTE("debug_sync_exec",
+                   if (thd->killed)
+                     DBUG_PRINT("debug_sync_exec",
+                                ("killed %d from '%s'  at: '%s'",
+                                 thd->killed, sig_wait, dsp_name));
+                   else
+                     DBUG_PRINT("debug_sync_exec",
+                                ("%s from '%s'  at: '%s'",
+                                 error ? "timeout" : "resume",
+                                 sig_wait, dsp_name)););
+
+      /*
+        We don't use enter_cond()/exit_cond(). They do not save old
+        mutex and cond. This would prohibit the use of DEBUG_SYNC
+        between other places of enter_cond() and exit_cond(). The
+        protected mutex must always unlocked _before_ mysys_var->mutex
+        is locked. (See comment in THD::exit_cond().)
+      */
+      pthread_mutex_unlock(&debug_sync_global.ds_mutex);
+      pthread_mutex_lock(&thd->mysys_var->mutex);
+      thd->mysys_var->current_mutex= old_mutex;
+      thd->mysys_var->current_cond= old_cond;
+      thd_proc_info(thd, old_proc_info);
+      pthread_mutex_unlock(&thd->mysys_var->mutex);
+
+    }
+    else
+    {
+      /* In case we don't wait, we just release the mutex. */
+      pthread_mutex_unlock(&debug_sync_global.ds_mutex);
+    } /* end if (action->wait_for.length()) */
+
+  } /* end if (action->execute) */
+
+  /* hit_limit is zero for infinite. Don't decrement unconditionally. */
+  if (action->hit_limit)
+  {
+    if (!--action->hit_limit)
+    {
+      thd->killed= THD::KILL_QUERY;
+      my_error(ER_DEBUG_SYNC_HIT_LIMIT, MYF(0));
+    }
+    DBUG_PRINT("debug_sync_exec", ("hit_limit: %lu  at: '%s'",
+                                   action->hit_limit, dsp_name));
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+
+/**
+  Execute requested action at a synchronization point.
+
+  @param[in]     thd                thread handle
+  @param[in]     sync_point_name    name of synchronization point
+  @param[in]     name_len           length of sync point name
+*/
+
+void debug_sync(THD *thd, const char *sync_point_name, size_t name_len)
+{
+  st_debug_sync_control *ds_control= thd->debug_sync_control;
+  st_debug_sync_action  *action;
+  DBUG_ENTER("debug_sync");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(sync_point_name);
+  DBUG_ASSERT(name_len);
+  DBUG_ASSERT(ds_control);
+  DBUG_PRINT("debug_sync_point", ("hit: '%s'", sync_point_name));
+
+  /* Statistics. */
+  ds_control->dsp_hits++;
+
+  if (ds_control->ds_active &&
+      (action= debug_sync_find(ds_control->ds_action, ds_control->ds_active,
+                               sync_point_name, name_len)) &&
+      action->activation_count)
+  {
+    /* Sync point is active (action exists). */
+    debug_sync_execute(thd, action);
+
+    /* Statistics. */
+    ds_control->dsp_executed++;
+
+    /* If action became inactive, remove it to shrink the search array. */
+    if (!action->activation_count)
+      debug_sync_remove_action(ds_control, action);
+  }
+
+  DBUG_VOID_RETURN;
+}
+
+#endif /* defined(ENABLED_DEBUG_SYNC) */