windows-tls: Implement TLS key destructors for native Windows.

* lib/windows-tls.h (glwthread_tls_process_destructors): New
declaration.
(GLWTHREAD_DESTRUCTOR_ITERATIONS): New macro.
* lib/windows-tls.c: Include <limits.h>, windows-once.h.
(dtor_table_init_once, dtor_table_lock: New variables.
(struct dtor): New type.
(dtor_table, dtors_count, dtors_used, dtors_allocated,
dtor_processing_threads): New variables.
(dtor_table_initialize, dtor_table_ensure_initialized,
dtor_table_shrink_used, glwthread_tls_process_destructors): New
functions.
(glwthread_tls_key_create, glwthread_tls_key_delete): Rewritten to
handle non-NULL destructors.
* modules/windows-tls (Depends-on): Add windows-once.
* lib/glthread/tls.h (glthread_tls_key_init, glthread_tls_key_destroy):
Use the functions declared in windows-tls.h.
* lib/threads.in.h (TSS_DTOR_ITERATIONS): Define using
GLWTHREAD_DESTRUCTOR_ITERATIONS.
* lib/windows-thread.c: Include windows-tls.h.
(wrapper_func, glwthread_thread_exit): Invoke
glwthread_tls_process_destructors.
* modules/windows-thread (Depends-on): Add windows-tls.

1 files changed, 291 insertions, 10 deletions

diff --git a/lib/windows-tls.c b/lib/windows-tls.c
index 0f1979e103..02dfdfb7d6 100644
--- a/lib/windows-tls.c
+++ b/lib/windows-tls.c
@@ -22,17 +22,9 @@
 #include "windows-tls.h"
 
 #include <errno.h>
+#include <limits.h>
 
-int
-glwthread_tls_key_create (glwthread_tls_key_t *keyp, void (*destructor) (void *))
-{
-  /* TODO: The destructor is unsupported.  */
-  (void) destructor;
-
-  if ((*keyp = TlsAlloc ()) == (DWORD)-1)
-    return EAGAIN;
-  return 0;
-}
+#include "windows-once.h"
 
 void *
 glwthread_tls_get (glwthread_tls_key_t key)
@@ -48,9 +40,298 @@ glwthread_tls_set (glwthread_tls_key_t key, void *value)
   return 0;
 }
 
+/* The following variables keep track of TLS keys with non-NULL destructor.  */
+
+static glwthread_once_t dtor_table_init_once = GLWTHREAD_ONCE_INIT;
+
+static CRITICAL_SECTION dtor_table_lock;
+
+struct dtor { glwthread_tls_key_t key; void (*destructor) (void *); };
+
+/* The table of dtors.  */
+static struct dtor *dtor_table;
+/* Number of active entries in the dtor_table.  */
+static unsigned int dtors_count;
+/* Valid indices into dtor_table are 0..dtors_used-1.  */
+static unsigned int dtors_used;
+/* Allocation size of dtor_table.  */
+static unsigned int dtors_allocated;
+/* Invariant: 0 <= dtors_count <= dtors_used <= dtors_allocated.  */
+
+/* Number of threads that are currently processing destructors.  */
+static unsigned int dtor_processing_threads;
+
+static void
+dtor_table_initialize (void)
+{
+  InitializeCriticalSection (&dtor_table_lock);
+  /* The other variables are already initialized to NULL or 0, respectively.  */
+}
+
+static void
+dtor_table_ensure_initialized (void)
+{
+  glwthread_once (&dtor_table_init_once, dtor_table_initialize);
+}
+
+/* Shrinks dtors_used down to dtors_count, by replacing inactive entries
+   with active ones.  */
+static void
+dtor_table_shrink_used (void)
+{
+  unsigned int i = 0;
+  unsigned int j = dtors_used;
+
+  for (;;)
+    {
+      BOOL i_found = FALSE;
+      BOOL j_found = FALSE;
+      /* Find the next inactive entry, from the left.  */
+      for (; i < dtors_count;)
+        {
+          if (dtor_table[i].destructor == NULL)
+            {
+              i_found = TRUE;
+              break;
+            }
+          i++;
+        }
+
+      /* Find the next active entry, from the right.  */
+      for (; j > dtors_count;)
+        {
+          j--;
+          if (dtor_table[j].destructor != NULL)
+            {
+              j_found = TRUE;
+              break;
+            }
+        }
+
+      if (i_found != j_found)
+        /* dtors_count was apparently wrong.  */
+        abort ();
+
+      if (!i_found)
+        break;
+
+      /* i_found and j_found are TRUE.  Swap the two entries.  */
+      dtor_table[i] = dtor_table[j];
+
+      i++;
+    }
+
+  dtors_used = dtors_count;
+}
+
+void
+glwthread_tls_process_destructors (void)
+{
+  unsigned int repeat;
+
+  dtor_table_ensure_initialized ();
+
+  EnterCriticalSection (&dtor_table_lock);
+  if (dtor_processing_threads == 0)
+    {
+      /* Now it's the appropriate time for shrinking dtors_used.  */
+      if (dtors_used > dtors_count)
+        dtor_table_shrink_used ();
+    }
+  dtor_processing_threads++;
+
+  for (repeat = GLWTHREAD_DESTRUCTOR_ITERATIONS; repeat > 0; repeat--)
+    {
+      unsigned int destructors_run = 0;
+
+      /* Iterate across dtor_table.  We don't need to make a copy of dtor_table,
+         because
+           * When another thread calls glwthread_tls_key_create with a non-NULL
+             destructor argument, this will possibly reallocate the dtor_table
+             array and increase dtors_allocated as well as dtors_used and
+             dtors_count, but it will not change dtors_used nor the contents of
+             the first dtors_used entries of dtor_table.
+           * When another thread calls glwthread_tls_key_delete, this will
+             possibly set some 'destructor' member to NULL, thus marking an
+             entry as inactive, but it will not otherwise change dtors_used nor
+             the contents of the first dtors_used entries of dtor_table.  */
+      unsigned int i_limit = dtors_used;
+      unsigned int i;
+
+      for (i = 0; i < i_limit; i++)
+        {
+          struct dtor current = dtor_table[i];
+          if (current.destructor != NULL)
+            {
+              /* The current dtor has not been deleted yet.  */
+              void *current_value = glwthread_tls_get (current.key);
+              if (current_value != NULL)
+                {
+                  /* The current value is non-NULL.  Run the destructor.  */
+                  glwthread_tls_set (current.key, NULL);
+                  LeaveCriticalSection (&dtor_table_lock);
+                  current.destructor (current_value);
+                  EnterCriticalSection (&dtor_table_lock);
+                  destructors_run++;
+                }
+            }
+        }
+
+      /* When all TLS values were already NULL, no further iterations are
+         needed.  */
+      if (destructors_run == 0)
+        break;
+    }
+
+  dtor_processing_threads--;
+  LeaveCriticalSection (&dtor_table_lock);
+}
+
+int
+glwthread_tls_key_create (glwthread_tls_key_t *keyp, void (*destructor) (void *))
+{
+  if (destructor != NULL)
+    {
+      dtor_table_ensure_initialized ();
+
+      EnterCriticalSection (&dtor_table_lock);
+      if (dtor_processing_threads == 0)
+        {
+          /* Now it's the appropriate time for shrinking dtors_used.  */
+          if (dtors_used > dtors_count)
+            dtor_table_shrink_used ();
+        }
+
+      while (dtors_used == dtors_allocated)
+        {
+          /* Need to grow the dtor_table.  */
+          unsigned int new_allocated = 2 * dtors_allocated + 1;
+          if (new_allocated < 7)
+            new_allocated = 7;
+          if (new_allocated <= dtors_allocated) /* overflow? */
+            new_allocated = UINT_MAX;
+
+          LeaveCriticalSection (&dtor_table_lock);
+          {
+            struct dtor *new_table =
+              (struct dtor *) malloc (new_allocated * sizeof (struct dtor));
+            if (new_table == NULL)
+              return ENOMEM;
+            EnterCriticalSection (&dtor_table_lock);
+            /* Attention! dtors_used, dtors_allocated may have changed!  */
+            if (dtors_used < new_allocated)
+              {
+                if (dtors_allocated < new_allocated)
+                  {
+                    /* The new_table is useful.  */
+                    memcpy (new_table, dtor_table,
+                            dtors_used * sizeof (struct dtor));
+                    dtor_table = new_table;
+                    dtors_allocated = new_allocated;
+                  }
+                else
+                  {
+                    /* The new_table is not useful, since another thread
+                       meanwhile allocated a drop_table that is at least
+                       as large.  */
+                    free (new_table);
+                  }
+                break;
+              }
+            /* The new_table is not useful, since other threads increased
+               dtors_used.  Free it any retry.  */
+            free (new_table);
+          }
+        }
+      /* Here dtors_used < dtors_allocated.  */
+      {
+        /* Allocate a new key.  */
+        glwthread_tls_key_t key = TlsAlloc ();
+        if (key == (DWORD)-1)
+          {
+            LeaveCriticalSection (&dtor_table_lock);
+            return EAGAIN;
+          }
+        /* Store the new dtor in the dtor_table, after all used entries.
+           Do not overwrite inactive entries with indices < dtors_used, in order
+           not to disturb glwthread_tls_process_destructors invocations that may
+           be executing in other threads.  */
+        dtor_table[dtors_used].key = key;
+        dtor_table[dtors_used].destructor = destructor;
+        dtors_used++;
+        dtors_count++;
+        LeaveCriticalSection (&dtor_table_lock);
+        *keyp = key;
+      }
+    }
+  else
+    {
+      /* Allocate a new key.  */
+      glwthread_tls_key_t key = TlsAlloc ();
+      if (key == (DWORD)-1)
+        return EAGAIN;
+      *keyp = key;
+    }
+  return 0;
+}
+
 int
 glwthread_tls_key_delete (glwthread_tls_key_t key)
 {
+  /* Should the destructor be called for all threads that are currently running?
+     Probably not, because
+       - ISO C does not specify when the destructor is to be invoked at all.
+       - In POSIX, the destructor functions specified with pthread_key_create()
+         are invoked at thread exit.
+       - It would be hard to implement, because there are no primitives for
+         accessing thread-specific values from a different thread.  */
+  dtor_table_ensure_initialized ();
+
+  EnterCriticalSection (&dtor_table_lock);
+  if (dtor_processing_threads == 0)
+    {
+      /* Now it's the appropriate time for shrinking dtors_used.  */
+      if (dtors_used > dtors_count)
+        dtor_table_shrink_used ();
+      /* Here dtors_used == dtors_count.  */
+
+      /* Find the key in dtor_table.  */
+      {
+        unsigned int i_limit = dtors_used;
+        unsigned int i;
+
+        for (i = 0; i < i_limit; i++)
+          if (dtor_table[i].key == key)
+            {
+              if (i < dtors_used - 1)
+                /* Swap the entries i and dtors_used - 1.  */
+                dtor_table[i] = dtor_table[dtors_used - 1];
+              dtors_count = dtors_used = dtors_used - 1;
+              break;
+            }
+      }
+    }
+  else
+    {
+      /* Be careful not to disturb the glwthread_tls_process_destructors
+         invocations that are executing in other threads.  */
+      unsigned int i_limit = dtors_used;
+      unsigned int i;
+
+      for (i = 0; i < i_limit; i++)
+        if (dtor_table[i].destructor != NULL /* skip inactive entries */
+            && dtor_table[i].key == key)
+          {
+            /* Mark this entry as inactive.  */
+            dtor_table[i].destructor = NULL;
+            dtors_count = dtors_count - 1;
+            break;
+          }
+    }
+  LeaveCriticalSection (&dtor_table_lock);
+  /* Now we have ensured that glwthread_tls_process_destructors will no longer
+     use this key.  */
+
   if (!TlsFree (key))
     return EINVAL;
   return 0;