c - 线程同步

Question

我有一个线程锁定互斥量，将值写入变量，然后解锁互斥量。 我在这里打印出来，值已经改变了。我将它设置为 1。

当我在另一个线程中使用锁读取变量值时，在互斥锁上解锁并读取值，我得到旧值 0。

为什么会这样。我正确地锁定和解锁同一个互斥体。

如何同步线程？

编辑:

我在这里声明了互斥量和变量

static pthread_mutex_t movementIdMutex = PTHREAD_MUTEX_INITIALIZER;
static int nav_movementId = 0;

static pthread_mutex_t newMovementMutex = PTHREAD_MUTEX_INITIALIZER;
static int nav_newMovement = 0;

我在这里设置变量

void nav_setMovementIdentifier(int id)
{
printf("Received movement id:%d from connectivity\n", id);

int result; /* Use the result for testing */

result = pthread_mutex_lock(&movementIdMutex);
nav_movementId = id;
printf("nav_movementId is %d\n", nav_movementId);
result = pthread_mutex_unlock(&movementIdMutex);

result = pthread_mutex_lock(&newMovementMutex);
nav_newMovement = 1;
printf("nav_newMovement is %d in the setId function\n", nav_newMovement);
result = pthread_mutex_unlock(&newMovementMutex);
printf("\n");
}

并在这里阅读它们

void *startConnectivityListener(void *ptr)     {

/* Declare safety variables because segments cant be locked/unlocked 
*  using mutexes if they are checking in statement such as if and while.
*/
int newMoveCheck = 0;
int startIndoorCheck = 0;
int startOutdoorCheck = 0;

int listening = 1;

while(listening == 1)
{
    int result; /* Use for testing */

    /* check if a new movement command waits */
    result = pthread_mutex_lock(&newMovementMutex);
    newMoveCheck = nav_newMovement;
    printf("nav new movement in thread is :%d\n", nav_newMovement);
    printf("newMoveCheck in mutex lock is:%d\n", newMoveCheck);
    result = pthread_mutex_unlock(&newMovementMutex);

    result = pthread_mutex_lock(&movementIdMutex);
    printf("nav_movementId in thread is %d\n", nav_movementId);
    result = pthread_mutex_unlock(&movementIdMutex);

    printf("newMoveCheck is %d\n", newMoveCheck);
    sleep(1);

    if(newMoveCheck == 1)

我在 setter 函数 printf 语句中得到了正确的打印输出，它将值设置为传入的 id 和 1。

当我尝试在我阅读它们的地方打印它时，两者仍显示 0，这是我初始化它们时设置的值。

Answer 1

尝试将 volatile 说明符添加到 nav_movementId 和 nav_newMovement 变量。