pthread_equal() alternative for powerpc cross compiler?

Question

I'm working on a program that reads the CAN datastream on a vehicle. The program will be used on an STW TC3g with an embedded linux.

I need to compile my code with a cross compiler based on the powerpc. For multithreading I wrote a little example program to test some functions.

Here is the code:

pthread_t tid[2];
void* thread_pollCan();

int main() {

    while(1) {
        pthread_create(&tid[0], NULL, &thread_pollCan, NULL);
        pthread_create(&tid[1], NULL, &thread_pollCan, NULL);
        printf("main:\tpid0:%ld\n", tid[0]);
        printf("main:\tpid1:%ld\n", tid[1]);
        pthread_join(tid[0],NULL);
        pthread_join(tid[1],NULL);
        puts("main:\tThreads terminated");
        sleep(3);
        puts("main:\tLoop end");
    }   

    return 0;
};

void* thread_pollCan(void* arg) {
        int  i;  

    // Should thread tid[0] do...
    if(pthread_equal(pthread_self(),tid[0])) {
        printf("tid[0]: %ld\t thread_self: %ld\n",tid[0],pthread_self());
        for(i=0;i<=10;i++) {
            printf("In loop %d\n",i);
        }   
    }   
    // Should thread tid[1] do...
    if(pthread_equal(pthread_self(),tid[1])) {
        printf("tid[1]: %ld\t thread_self: %ld\n",tid[1],pthread_self());
        for(i=0;i<=10;i++) {
            printf("In loop %d\n",i);
        }
    }
    pthread_exit((void *)pthread_self());
}

This program runs fine on my developing ubuntu pc if I compile it with gcc:

  gcc -Wall -pthread Multithreading.c -o Multithreading

Program output:

    main:   pid0:140207930042112
    main:   pid1:140207921649408
    tid[0]: 140207930042112  thread_self: 140207930042112
    In loop 0
    In loop 1
    In loop 2
    In loop 3
    In loop 4
    In loop 5
    In loop 6
    In loop 7
    In loop 8
    In loop 9
    In loop 10
    tid[1]: 140207921649408  thread_self: 140207921649408
    In loop 0
    In loop 1
    In loop 2
    In loop 3
    In loop 4
    In loop 5
    In loop 6
    In loop 7
    In loop 8
    In loop 9
    In loop 10
    main:   Threads terminated
    main:   Loop end

But if I compile it for my vehicle computer with the following:

powerpc-stw-linux-uclibc-gcc -O2 -Wall -pthread  Multithreading.c -o Multithreading -lm

Its program output is this:

main:   pid0:1026
main:   pid1:2051
main:   Threads terminated
main:   Loop end

The problem is, that the pthread_equal() function never match with the thread id wrote in the tid[]-array.

So my question is, if there are any other methods to find the correct thread id.

Answer 1

Seems you're trying to read tid[] that does not have the time to get updated. You should add some mutex function calls to synchronize all:

// mutex for synchronization
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

// pthread ids
pthread_t tid[2];

// thread function
void* thread_pollCan();

int main() {
    while(1) {
        // lock the mutex: thread will wait for it to be unlocked
        pthread_mutex_lock(&mutex);

        pthread_create(&tid[0], NULL, &thread_pollCan, NULL);
        pthread_create(&tid[1], NULL, &thread_pollCan, NULL);
        printf("main:\tpid0:%ld\n", tid[0]);
        printf("main:\tpid1:%ld\n", tid[1]);

        // unlock the mutex: threads can run
        pthread_mutex_unlock(&mutex);

        pthread_join(tid[0],NULL);
        pthread_join(tid[1],NULL);
        puts("main:\tThreads terminated");
        sleep(3);
        puts("main:\tLoop end");
    }   

    return 0;
};

void* thread_pollCan(void* arg) {

    // wait for mutex to be unlocked before working
    pthread_mutex_lock(&mutex);

    // immediatly release the mutex
    pthread_mutex_unlock(&mutex);

    // do stuff
    if (thread_equal(tid[0], pthread_self())
    {  /*...*/ }
}