Thread-Safe Functions

[scioner]

Hello,

I was wondering how to make malloc() thread safe. Could I just use a mutex everytime I use malloc() in my code example

pthread_mutex_lock(&malloc_mutex);
   // Malloc Code here
pthread_mutex_unlock(&malloc_mutex);

And if that's the case could I make any function thread safe that way?

Thanks,
scioner

[Elysia]

Sure. The only problem is that some implementations already do locking (such as Visual Studio), in which case you'd be locking twice. But otherwise, that's how you would want to do it. Or you may use critical sections which are faster.
EDIT: On Windows.

[vart]

Or you may use critical sections which are faster

Which depends on the conflict probability

[Codeplug]

malloc() is thread safe under a POSIX sytem supporting threads.
http://www.opengroup.org/onlinepubs/...l#tag_02_09_01

>> could I make any function thread safe that way?
In the most general sense, yes.

gg

[brewbuck]

Hello,

I was wondering how to make malloc() thread safe. Could I just use a mutex everytime I use malloc() in my code

I would definitely not recommend wrapping every call to malloc() in a lock. If you have a thread-unsafe malloc(), you should write a thread safe function (e.g. threadsafe_malloc()) which does the locking/unlocking for you. And of course similar functions for realloc() and free(). Doing it explicitly everywhere would be redundant, and open the possibility of forgetting.

And if that's the case could I make any function thread safe that way?

Simply adding locks does not necessarily make a function thread safe. You have to consider deadlock conditions as well. Also, think about what might happen (if anything) if a signal is delivered at any particular point.

Most platforms capable of threading have a native thread safe malloc(). You should use it, if available. It probably does optimizations which give better performance than just wrapping everything in locks.

Failing that, you may be able to write a custom allocator which is thread safe without requiring locks. But a global lock around all calls to malloc() is probably the least preferred solution.

[scioner]

wow I was overwhelmed by the responses thank you very much, very quick and to the point all the answers.


I wrote a library with 3 functions

log_write() -> Writes to log file
log_make_date() -> Generates the current time and date
log_make_stamp() -> Creates Time Stamp

Now log_make_date() makes use of gettimeofday() and localtime().

I am using this small library in a multi-threaded application and I understand that gettimeofday() is not thread-safe. I need to make this function thread-safe or find an thread-safe implementation, any help would be greatly appreciated.

Thanks in advance

[scioner]

Never Mind I was missinformed by a post I now find out that gettimeofday is thread safe because it doesn't required static data and localtime() well there is a thread safe version localtime_r() thanks anyways. Sorry for posting without researching further

Thanks