CODEWITHSUNDEEP
cwinapimutex
AnArrayOfFunctions
AnArrayOfFunctions

Reputation: 3744

Simple mutex application isn't working correctly?

Consider this code:

#include  <Windows.h>

test(HANDLE*hB0)
{
    printf("hello "), ReleaseMutex(*hB0);
}
main()
{
    HANDLE hB0;
        CreateThread(0,0,test,(hB0=CreateMutex(NULL,true,NULL),&hB0),0,0),
        WaitForSingleObject(hB0, INFINITE),
        printf("world!");
}

I'm expecting to get hello world! but I'm just getting world! instead. Any ideas why?

I tried with second parameter to CreateMutex both true & false but it is still not working.

Upvotes: 0

Views: 325

Answers (1)

RbMm
RbMm

Reputation: 33706

from CreateMutex function

The thread that owns a mutex can specify the same mutex in repeated wait function calls without blocking its execution

in call 

hB0=CreateMutex(NULL,true,NULL)

the bInitialOwner = TRUE so your current thread own the mutex, as result WaitForSingleObject(hB0, INFINITE) just return without blocking execution.

from another side if thread, which not own mutex, call ReleaseMutex - will be error returned ERROR_NOT_OWNER - Attempt to release mutex not owned by caller. or native status STATUS_MUTANT_NOT_OWNED An attempt to release a mutant object was made by a thread that was not the owner of the mutant object. - but you not check function result and error code.

also because you define test(HANDLE*hB0) - you need call ReleaseMutex(*hB0); instead ReleaseMutex(hB0);. however better pass hB0 handle direct to thread as argument, instead pointer &hB0 to handle.

Upvotes: 3

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