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05.13.2008 at 03:06PM PDT, ID: 23399628

	[x] Attachment Details

thread safety and malloc/free

Asked by chsalvia in C Programming Language

As far as I know, the C standard is silent about the thread-safety of malloc and free (and anything else concerning threads, for that matter.)

I've developed a lot of multithreaded programs using POSIX threads, and I have never had a problem with malloc/free. So I assume that on my implementation malloc/free are thread safe. (I'm using GCC 4.1.2 on Linux Debian 4)

However, I've read complaints on the Internet about random crashes with multi-threaded programs that use malloc/free.

So, is the use of mutexes in combination with malloc/free a requirement for writing portable code? I never use mutexes for malloc/free, so I fear porting my code to other platforms/compilers may require a bit of work. Start Free Trial

Keywords: thread safety and malloc/free

	Title
1	Malloc
2	malloc and new???
3	Malloc space for pointers
4	car safety
5	MALLOC
6	Built in types and thread-safety

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05.13.2008 at 03:51PM PDT, ID: 21559955

jaime_olivares:

I think this is a problem of specific implementations of C compiler/library.
ANSI C is not aware about threads, it is a POSIX extension.
So, you should provide some kind of protection by yourself.
Also, make sure your compiler has a thread-safe library.

Assisted Solution

05.13.2008 at 04:39PM PDT, ID: 21560189

evilrix:

Access to the free store is implementation dependent; however, I can tell you that Windows will protect it with a mutex providing you are using the multi-threading C runtime, otherwise all bets are off. For a C runtime to be Posix compliant it should be thread safe; however, you should always refer to the documentation for your C runtime library.

Assisted Solution

05.14.2008 at 12:31AM PDT, ID: 21561845

Infinity08:

The GNU C library (glibc) is thread safe (and POSIX compliant) if you link the pthread library to the application (unless you're using a very old version of glibc). That includes malloc :)

Accepted Solution

05.14.2008 at 06:16AM PDT, ID: 21563774

Gurudenis:

Changing your implementations to be thread-safe won't require much work. I'd do it like this (pseudocode):

                       
             void* my_malloc(size_t size)
{
    // Acquire mutex ...
 
    void* p = malloc(size);
 
    // Release mutex ...
 
    return p;
}
 
#define malloc(size) my_malloc(size)

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Assisted Solution

05.14.2008 at 06:26AM PDT, ID: 21563869

evilrix:

>> Changing your implementations to be thread-safe won't require much work. I'd do it like this (pseudocode):
It's probably unnecessary. Like I said, you should check the C runtime docs but both Windows MT CRT and Linux glibc are thread safe. This being the case, doing this will just add an extra unnecessary level of complexity and contention into the code base.

05.14.2008 at 06:46AM PDT, ID: 21564093

Gurudenis:

Yes, I just showed the way to go if the code needs to be ported to thread unsafe implementations of standard library. Of course it's an unnecessary trick with most popular implementations.

If at some point this code must be compiled with unsafe malloc/free, the declaration of my_malloc() can be placed in an #ifdef block to ensure it's only used with that particular library or compiler, anyway.

20080716-EE-VQP-32 / EE_QW_2_20070628

thread safety and malloc/free

Asked by chsalvia in C Programming Language

About this solution