Is this code memory leak free? ---> POSIX Threads

This is a discussion on Is this code memory leak free? ---> POSIX Threads within the C++ Programming forums, part of the General Programming Boards category; Here is a small sample of what I am doing without much of the logic.. basically the threading part. Could ...

  1. #1
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    Is this code memory leak free? ---> POSIX Threads

    Here is a small sample of what I am doing without much of the logic.. basically the threading part. Could someone tell me if this is memory leak free?

    If it is not, what could I do to make it memory leak free.

    Thanks,

    Code:
    pthread_mutex_t hMutex = PTHREAD_MUTEX_INITIALIZER;
    
    
    void SendFile()
    {
    	if ( pthread_mutex_lock( &hMutex ) != 0 )
    		cout << "Error locking mutex" << endl;
    
    	/* Some Code... */
    
    	if ( pthread_mutex_unlock( &hMutex ) != 0 )
    		cout << "Error unlocking mutex" << endl;
    
    	pthread_exit( NULL );
    }
    
    void Run()
    {
    	/*Some Code....*/
    	pthread_t uploadThread = {0};
    	if( pthread_create( &uploadThread, NULL, (void*(*)(void*))SendFile, NULL ) != 0 )
    		cout << "Error creating thread" << endl;
    }
    int main()
    {
    	Run();
    	pthread_mutex_destroy( &hMutex );
    	return 0;
    }

  2. #2
    and the hat of wrongness Salem's Avatar
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    > (void*(*)(void*))SendFile
    If you get the declaration of the function right, then this cast is not needed.

    > pthread_mutex_destroy( &hMutex );
    Maybe no leak, but deleting the mutex before you get a chance to use it would be bad.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    What is the right way to declare it?

    I think it was something like SendFile( void** pVal ), then pass SendFile by reference.

    With regards to the mutex... is is created/initalized with

    Code:
    pthread_mutex_t hMutex = PTHREAD_MUTEX_INITIALIZER;
    I would think that would take care of it.. but if not, I acually do use joins before i destroy the threads, just forgot to put them in here.

    Thanks.

  4. #4
    and the hat of wrongness Salem's Avatar
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    > What is the right way to declare it?
    The thread that creates it should be the thread that deletes it.

    > I acually do use joins before i destroy the threads, just forgot to put them in here.
    Oh well, if you want an ACCURATE response then, you know what to do.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
    Cat without Hat CornedBee's Avatar
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    What is the right way to declare it?
    I think by "it" he meant the function, Salem.

    The right way is, as the pointer signature and the manpage for pthread_create say:
    Code:
    void *SendFile(void *arg)
    For the meaning of the return value, see pthread_exit and pthread_join.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  6. #6
    Frequently Quite Prolix dwks's Avatar
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    Assuming you're using Linux, Valgrind is a great tool for detecting memory leaks: valgrind.org

    I find it doesn't help you fix memory leaks as much as detect them, though.
    dwk

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    Yes I am in linux. I'll try it out, thanks for the suggestion. I've been looking for something like this and ran into a few programs but they seemed to conly catch basic memory leaks... dumb things like if you new something do you delete it. But i do need something to catch more advanced leaks then this. Thanks again

  8. #8
    Cat without Hat CornedBee's Avatar
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    Umm ... all memory leaks involve not deleting memory that was allocated. You can also have memory errors, where you delete something that wasn't allocated or delete something twice or use the wrong deletion form, but those aren't leaks (and they're detected by a normal allocator, except for the last one). Then there are resource leaks, of which memory leaks are one case. Other resource leaks involved allocating mutexes, network connections and other stuff that is in limited supply and not freeing them - but valgrind doesn't detect most of these.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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    ah, thank for the heads up

  10. #10
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by avalanche333 View Post
    Code:
    void Run()
    {
    	/*Some Code....*/
    	pthread_t uploadThread = {0};
    	if( pthread_create( &uploadThread, NULL, (void*(*)(void*))SendFile, NULL ) != 0 )
    		cout << "Error creating thread" << endl;
    }
    int main()
    {
    	Run();
    	pthread_mutex_destroy( &hMutex );
    	return 0;
    }
    This isn't even right. The code that calls pthread_create() has to either do a pthread_join() to wait for the spawned thread to finish, or call pthread_detach() on it. Since the code you posted contains no memory allocations anywhere, there is obviously no memory leak here, except for the created thread itself (since like I said, you never pthread_join() it!)

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