您需要做的是调用pthread_mutex_lock来保护互斥锁，如下所示：

pthread_mutex_lock(&mutex);

一旦执行此操作，pthread_mutex_lock(mutex)在您pthread_mutex_unlock在该线程中进行调用之前，不会再进行任何其他调用。因此，如果尝试调用pthread_create，则将能够创建一个新线程，并且该线程将能够（不正确地）使用共享资源。您应该pthread_mutex_lock在fooAPI函数内部进行调用，这将导致函数等待，直到共享资源可用为止。

所以你会有这样的事情：

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

int sharedResource = 0;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void* fooAPI(void* param)
{
    pthread_mutex_lock(&mutex);
    printf("Changing the shared resource now.\n");
    sharedResource = 42;
    pthread_mutex_unlock(&mutex);
    return 0;
}

int main()
{
    pthread_t thread;

    // Really not locking for any reason other than to make the point.
    pthread_mutex_lock(&mutex);
    pthread_create(&thread, NULL, fooAPI, NULL);
    sleep(1);
    pthread_mutex_unlock(&mutex);

    // Now we need to lock to use the shared resource.
    pthread_mutex_lock(&mutex);
    printf("%d\n", sharedResource);
    pthread_mutex_unlock(&mutex);
}

编辑：跨进程使用资源遵循相同的基本方法，但是您需要将内存映射到其他进程。这是使用shmem的示例：

#include <stdio.h>
#include <unistd.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/wait.h>

struct shared {
    pthread_mutex_t mutex;
    int sharedResource;
};

int main()
{
    int fd = shm_open("/foo", O_CREAT | O_TRUNC | O_RDWR, 0600);
    ftruncate(fd, sizeof(struct shared));

    struct shared *p = (struct shared*)mmap(0, sizeof(struct shared),
        PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

    p->sharedResource = 0;

    // Make sure it can be shared across processes
    pthread_mutexattr_t shared;
    pthread_mutexattr_init(&shared);
    pthread_mutexattr_setpshared(&shared, PTHREAD_PROCESS_SHARED);

    pthread_mutex_init(&(p->mutex), &shared);

    int i;
    for (i = 0; i < 100; i++) {
        pthread_mutex_lock(&(p->mutex));
        printf("%d\n", p->sharedResource);
        pthread_mutex_unlock(&(p->mutex));
        sleep(1);
    }

    munmap(p, sizeof(struct shared*));
    shm_unlink("/foo");
}

编写程序以更改p-> sharedResource留给读者练习。:-)

顺便说一句，忘了指出互斥对象必须设置PTHREAD_PROCESS_SHARED属性，这样pthread才能跨进程工作。