Bug#34043: Server loops excessively in _checkchunk() when safemalloc is enabled

Essentially, the problem is that safemalloc is excruciatingly
slow as it checks all allocated blocks for overrun at each
memory management primitive, yielding a almost exponential
slowdown for the memory management functions (malloc, realloc,
free). The overrun check basically consists of verifying some
bytes of a block for certain magic keys, which catches some
simple forms of overrun. Another minor problem is violation
of aliasing rules and that its own internal list of blocks
is prone to corruption.

Another issue with safemalloc is rather the maintenance cost
as the tool has a significant impact on the server code.
Given the magnitude of memory debuggers available nowadays,
especially those that are provided with the platform malloc
implementation, maintenance of a in-house and largely obsolete
memory debugger becomes a burden that is not worth the effort
due to its slowness and lack of support for detecting more
common forms of heap corruption.

Since there are third-party tools that can provide the same
functionality at a lower or comparable performance cost, the
solution is to simply remove safemalloc. Third-party tools
can provide the same functionality at a lower or comparable
performance cost. 

The removal of safemalloc also allows a simplification of the
malloc wrappers, removing quite a bit of kludge: redefinition
of my_malloc, my_free and the removal of the unused second
argument of my_free. Since free() always check whether the
supplied pointer is null, redudant checks are also removed.

Also, this patch adds unit testing for my_malloc and moves
my_realloc implementation into the same file as the other
memory allocation primitives.

client/mysqldump.c:
  Pass my_free directly as its signature is compatible with the
  callback type -- which wasn't the case for free_table_ent.

1 files changed, 88 insertions, 30 deletions

diff --git a/mysys/my_malloc.c b/mysys/my_malloc.c
index 13d2375eb99..fc2dc98c3c5 100644
--- a/mysys/my_malloc.c
+++ b/mysys/my_malloc.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000 MySQL AB
+/* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
 
    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
@@ -11,28 +11,31 @@
 
    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 */
-
-#ifdef SAFEMALLOC			/* We don't need SAFEMALLOC here */
-#undef SAFEMALLOC
-#endif
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
 #include "mysys_priv.h"
 #include "mysys_err.h"
 #include <m_string.h>
 
-	/* My memory allocator */
+/**
+  Allocate a sized block of memory.
 
+  @param size   The size of the memory block in bytes.
+  @param flags  Failure action modifiers (bitmasks).
+
+  @return A pointer to the allocated memory block, or NULL on failure.
+*/
 void *my_malloc(size_t size, myf my_flags)
 {
   void* point;
   DBUG_ENTER("my_malloc");
   DBUG_PRINT("my",("size: %lu  my_flags: %d", (ulong) size, my_flags));
 
+  /* Safety */
   if (!size)
-    size=1;					/* Safety */
+    size=1;
 
-  point= (char *) malloc(size);
+  point= malloc(size);
   DBUG_EXECUTE_IF("simulate_out_of_memory",
                   {
                     free(point);
@@ -52,33 +55,87 @@ void *my_malloc(size_t size, myf my_flags)
       exit(1);
   }
   else if (my_flags & MY_ZEROFILL)
-    bzero(point,size);
-  DBUG_PRINT("exit",("ptr: 0x%lx", (long) point));
-  DBUG_RETURN((void*) point);
-} /* my_malloc */
+    bzero(point, size);
+  DBUG_PRINT("exit",("ptr: %p", point));
+  DBUG_RETURN(point);
+}
+
+
+/**
+   @brief wrapper around realloc()
+
+   @param  oldpoint        pointer to currently allocated area
+   @param  size            new size requested, must be >0
+   @param  my_flags        flags
+
+   @note if size==0 realloc() may return NULL; my_realloc() treats this as an
+   error which is not the intention of realloc()
+*/
+void *my_realloc(void *oldpoint, size_t size, myf my_flags)
+{
+  void *point;
+  DBUG_ENTER("my_realloc");
+  DBUG_PRINT("my",("ptr: %p  size: %lu  my_flags: %d", oldpoint,
+                   (ulong) size, my_flags));
+
+  DBUG_ASSERT(size > 0);
+  if (!oldpoint && (my_flags & MY_ALLOW_ZERO_PTR))
+    DBUG_RETURN(my_malloc(size, my_flags));
+#ifdef USE_HALLOC
+  if (!(point = malloc(size)))
+  {
+    if (my_flags & MY_FREE_ON_ERROR)
+      my_free(oldpoint);
+    if (my_flags & MY_HOLD_ON_ERROR)
+      DBUG_RETURN(oldpoint);
+    my_errno=errno;
+    if (my_flags & MY_FAE+MY_WME)
+      my_error(EE_OUTOFMEMORY, MYF(ME_BELL+ME_WAITTANG),size);
+  }
+  else
+  {
+    memcpy(point,oldpoint,size);
+    free(oldpoint);
+  }
+#else
+  if ((point= realloc(oldpoint, size)) == NULL)
+  {
+    if (my_flags & MY_FREE_ON_ERROR)
+      my_free(oldpoint);
+    if (my_flags & MY_HOLD_ON_ERROR)
+      DBUG_RETURN(oldpoint);
+    my_errno=errno;
+    if (my_flags & (MY_FAE+MY_WME))
+      my_error(EE_OUTOFMEMORY, MYF(ME_BELL+ME_WAITTANG), size);
+  }
+#endif
+  DBUG_PRINT("exit",("ptr: %p", point));
+  DBUG_RETURN(point);
+}
 
 
-	/* Free memory allocated with my_malloc */
-	/*ARGSUSED*/
+/**
+  Free memory allocated with my_malloc.
 
-void my_no_flags_free(void* ptr)
+  @remark Relies on free being able to handle a NULL argument.
+
+  @param ptr Pointer to the memory allocated by my_malloc.
+*/
+void my_free(void *ptr)
 {
   DBUG_ENTER("my_free");
-  DBUG_PRINT("my",("ptr: 0x%lx", (long) ptr));
-  if (ptr)
-    free(ptr);
+  DBUG_PRINT("my",("ptr: %p", ptr));
+  free(ptr);
   DBUG_VOID_RETURN;
-} /* my_free */
-
+}
 
-	/* malloc and copy */
 
-void* my_memdup(const void *from, size_t length, myf my_flags)
+void *my_memdup(const void *from, size_t length, myf my_flags)
 {
   void *ptr;
   if ((ptr= my_malloc(length,my_flags)) != 0)
     memcpy(ptr, from, length);
-  return(ptr);
+  return ptr;
 }
 
 
@@ -87,18 +144,19 @@ char *my_strdup(const char *from, myf my_flags)
   char *ptr;
   size_t length= strlen(from)+1;
   if ((ptr= (char*) my_malloc(length, my_flags)))
-    memcpy((uchar*) ptr, (uchar*) from,(size_t) length);
-  return(ptr);
+    memcpy(ptr, from, length);
+  return ptr;
 }
 
 
 char *my_strndup(const char *from, size_t length, myf my_flags)
 {
   char *ptr;
-  if ((ptr= (char*) my_malloc(length+1,my_flags)) != 0)
+  if ((ptr= (char*) my_malloc(length+1, my_flags)))
   {
-    memcpy((uchar*) ptr, (uchar*) from, length);
-    ptr[length]=0;
+    memcpy(ptr, from, length);
+    ptr[length]= 0;
   }
-  return((char*) ptr);
+  return ptr;
 }
+