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Programming: Windows Threading Vs Linux Threading (Part 6)

A thread cleanup handler in Linux and Windows thread cancellation:

A cleanup handler is a measure, used to deallocate a resource only if the thread exits or canceled. To register a cleanup handler, need to call pthread_cleanup_push() and
pass a pointer to cleanup function and the void * argument. The pthread_cleanup_pop() function removes the routine at the top of the calling thread's cancellation cleanup
stack and optionally invokes it (if execute is non-zero).

The following sample code shows how a dynamically allocated buffer from a thread can be deallocated on canceling the thread in Linux.

#include < pthread.h >
#include < stdio.h >
#include < string.h >
#include < unistd.h > 

char *pgArray = 0;

/* Buffer allocation */
char * allocate_array (size_t size)
{
    return new char[size];
}

void release_array (void *pArg)
{
    if(pgArray)
    {
        printf("release_array() called..\n");
        delete []pgArray;
    }
}

void *Print_Details(void *param)
{
    printf("This is secondary thread's entry...\n");
    printf("Allocating a buffer of size 20...\n");

    pgArray = allocate_array(20);
    strcpy(pgArray, "This is a test");
   
    /*Registering the cleanup handler in case thread cancelled/exit*/
    pthread_cleanup_push(release_array, NULL);

    size_t sIndex = 0;

    // An infinite loop to keep the thread busy until thread cancel gets called...   
    while (pgArray[sIndex] != '\0')
    {
        printf ("%c\n", pgArray[sIndex]);
        sIndex++;
        if(pgArray[sIndex] == '\0')
        {
            sleep(1);
            sIndex = 0;
        }   
    }
   
    printf("This is secondary thread's exit...\n");
    /*Unregister the cleanup handler by passing a nonzero value,
    this actually calls the release_array()*/
    pthread_cleanup_pop(1);
   
    return NULL;
}

/* Main program */

int main()
{
    pthread_t thread;
    int thread_ret;
    void *status;

    printf("This is main... Creating thread with default param\n");   
    pthread_create(&thread, NULL, &Print_Details, NULL);

    sleep(1);   
    // Called secondary thread cancellation....
    printf("Called secondary thread cancellation...\n");
    pthread_cancel(thread);
   
    sleep(2);
    printf("Main exited\n");
   
    return 0;
}

In Windows, as per Microsoft we should call TerminateThread only when there is no other go. Then the question comes what's the way in Windows, a thread/threads can be
canceled/stopped as required. Microsoft provided a way to do this by implementing following steps:

a.    Create an event object using the CreateEvent function.
b.    Create the threads.
c.    Each thread monitors the event state by calling the WaitForSingleObject function. Use a wait time-out interval of zero.
d.    Each thread terminates its own execution when the event is set to the signaled state (WaitForSingleObject returns WAIT_OBJECT_0).

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