UC知道一个关于apue里的问题
来源：百度知道 编辑：UC知道 时间：2024/05/10 05:28:39
apue里有这一段：
We need to ensure that a key we allocate doesn't change because of a race during initialization. Code like the following can result in two threads both calling pthread_key_create:
void destructor(void *);
pthread_key_t key;
int init_done = 0;
int
threadfunc(void *arg)
{
if (!init_done) {
init_done = 1;
err = pthread_key_create(&key, destructor);
}
...
}
Depending on how the system schedules threads, some threads might see one key value, whereas other threads might see a different value.
这段看不懂，为什么导致两个线程都调用pthread_key_create
We need to ensure that a key we allocate doesn't change because of a race during initialization. Code like the following can result in two threads both calling pthread_key_create:
void destructor(void *);
pthread_key_t key;
int init_done = 0;
int
threadfunc(void *arg)
{
if (!init_done) {
init_done = 1;
err = pthread_key_create(&key, destructor);
}
...
}
Depending on how the system schedules threads, some threads might see one key value, whereas other threads might see a different value.
这段看不懂，为什么导致两个线程都调用pthread_key_create
如果同时定义了2个pthread_t tid1, tid2;
然后创建了2个线程采用同一个线程callback函数pthread_create(&tid1, NULL, threadfunc, 1); pthread_create(&tid2, NULL, threadfunc, 2); 那么就会同时调用pthread_key_create函数.
因为pthread_key_create函数在线程处理函数中, 线程又是并行运行的.
apue是本好书啊......