pthread_cond_wait 详解
配套使用。pthread_cond_wait()函数一进入wait状态就会自动release mutex。当其他线程通过pthread_cond_signal()或pthread_cond_broadcast,把该线程唤醒,使pthread_cond_wait()通过(返回)时,该线程又自动获得该mutex。
wait,而且规范要求pthread_cond_signal至少唤醒一个pthread_cond_wait上的线程,其实有些实现为了简单在单处理器上也会唤醒多个线程.
int x,y;pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_mutex_lock(&mut);while (x <= y) {pthread_cond_wait(&cond, &mut);}/* operate on x and y */pthread_mutex_unlock(&mut);
pthread_mutex_lock(&mut);/* modify x and y */if (x > y) pthread_cond_broadcast(&cond);pthread_mutex_unlock(&mut);
#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <pthread.h>#define BUFFER_SIZE 8struct Products{int buffer[BUFFER_SIZE];/*保证存取操作的原子性 互斥性*/pthread_mutex_t locker;/*是否可读*/pthread_cond_t notEmpty;/*是否可写*/pthread_cond_t notFull;int posReadFrom;int posWriteTo;};int BufferIsFull(struct Products* products){if ((products->posWriteTo + 1) % BUFFER_SIZE == products->posReadFrom){return (1);}return (0);}int BufferIsEmpty(struct Products* products){if (products->posWriteTo == products->posReadFrom){return (1);}return (0);}/*制造产品*/。void Produce(struct Products* products, int item){/*原子操作*/pthread_mutex_lock(&products->locker);/*无空间可写入*/while (BufferIsFull(products)){pthread_cond_wait(&products->notFull, &products->locker);}/*写入数据*/products->buffer[products->posWriteTo] = item;products->posWriteTo++;if (products->posWriteTo >= BUFFER_SIZE)products->posWriteTo = 0;/*发信*/pthread_cond_signal(&products->notEmpty);/*解锁*/pthread_mutex_unlock(&products->locker);}int Consume(struct Products* products){int item;pthread_mutex_lock(&products->locker);/*为空时持续等待,无数据可读*/while (BufferIsEmpty(products)){pthread_cond_wait(&products->notEmpty, &products->locker);}/*提取数据*/item = products->buffer[products->posReadFrom];products->posReadFrom++;/*如果到末尾,从头读取*/if (products->posReadFrom >= BUFFER_SIZE)products->posReadFrom = 0;pthread_cond_signal(&products->notFull);pthread_mutex_unlock(&products->locker);return item;}#define END_FLAG (-1)struct Products products;void* ProducerThread(void* data){int i;for (i = 0; i < 16; ++i){printf("producer: %d\n", i);Produce(&products, i);}Produce(&products, END_FLAG);return NULL;}void* ConsumerThread(void* data){int item;while (1){item = Consume(&products);if (END_FLAG == item)break;printf("consumer: %d\n", item);}return (NULL);}int main(int argc, char* argv[]){pthread_t producer;pthread_t consumer;int result;pthread_create(&producer, NULL, &ProducerThread, NULL);pthread_create(&consumer, NULL, &ConsumerThread, NULL);pthread_join(producer, (void *)&result);pthread_join(consumer, (void *)&result);exit(EXIT_SUCCESS);}
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
pthread_mutex_t mymutex1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mymutex2 = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t mycond = PTHREAD_COND_INITIALIZER;
void *mythread1(void *param)
{
printf("begin mythread1.\n");
pthread_mutex_lock(&mymutex1);
printf("wait in mythread1.\n");
pthread_cond_wait(&mycond,&mymutex1);
pthread_mutex_unlock(&mymutex1);
printf("end mythread1.\n");
return NULL;
}
void *mythread2(void *param)
{
printf("begin mythread2.\n");
pthread_mutex_lock(&mymutex2);
printf("wait in mythread2.\n");
pthread_cond_wait(&mycond,&mymutex2);
pthread_mutex_unlock(&mymutex2);
printf("end mythread2.\n");
return NULL;
}
int main(void)
{
printf("begin main thread.\n");
int i;
pthread_t tid1,tid2;
pthread_create(&tid1,NULL,mythread1,NULL);
pthread_create(&tid2,NULL,mythread2,NULL);
sleep(5);
printf("try to wake up mythread1 and mythread2 in main thread.\n");
if(pthread_cond_broadcast(&mycond)){
printf("error\n");
return 1;
}
void *res;
pthread_join(tid1, &res);
pthread_join(tid2, &res);
printf("end main thread.\n");
return 0;
}
- #include <pthread.h>
- #include <stdlib.h>
- #include <stdio.h>
- #include <unistd.h>
- #include <string.h>
- pthread_mutex_t mymutex1 = PTHREAD_MUTEX_INITIALIZER;
- pthread_mutex_t mymutex2 = PTHREAD_MUTEX_INITIALIZER;
- pthread_cond_t mycond = PTHREAD_COND_INITIALIZER;
- void *mythread1(void *param)
- {
- printf("begin mythread1.\n");
- pthread_mutex_lock(&mymutex1);
- printf("wait in mythread1.\n");
- pthread_cond_wait(&mycond,&mymutex1);
- pthread_mutex_unlock(&mymutex1);
- printf("end mythread1.\n");
- return NULL;
- }
- void *mythread2(void *param)
- {
- printf("begin mythread2.\n");
- pthread_mutex_lock(&mymutex2);
- printf("wait in mythread2.\n");
- pthread_cond_wait(&mycond,&mymutex2);
- pthread_mutex_unlock(&mymutex2);
- printf("end mythread2.\n");
- return NULL;
- }
- int main(void)
- {
- printf("begin main thread.\n");
- int i;
- pthread_t tid1,tid2;
- pthread_create(&tid1,NULL,mythread1,NULL);
- pthread_create(&tid2,NULL,mythread2,NULL);
- sleep(2);
- printf("try to wake up mythread1 and mythread2 in main thread.\n");
- if(pthread_cond_broadcast(&mycond)){
- printf("error\n");
- return 1;
- }
- void *res;
- pthread_join(tid1, &res);
- pthread_join(tid2, &res);
- printf("end main thread.\n");
- return 0;
- }
begin main thread.
begin mythread1.
wait in mythread1.
begin mythread2.
wait in mythread2.
end mythread2.
try to wake up mythread1 and mythread2 in main thread.
end mythread1.
end main thread.
- #include <pthread.h>
- #include <stdlib.h>
- #include <stdio.h>
- #include <unistd.h>
- #include <string.h>
- pthread_mutex_t mymutex1 = PTHREAD_MUTEX_INITIALIZER;
- //pthread_mutex_t mymutex2 = PTHREAD_MUTEX_INITIALIZER;
- pthread_cond_t mycond = PTHREAD_COND_INITIALIZER;
- void *mythread1(void *param)
- {
- printf("begin mythread1.\n");
- pthread_mutex_lock(&mymutex1);
- printf("wait in mythread1.\n");
- pthread_cond_wait(&mycond,&mymutex1);
- pthread_mutex_unlock(&mymutex1);
- printf("end mythread1.\n");
- return NULL;
- }
- void *mythread2(void *param)
- {
- printf("begin mythread2.\n");
- pthread_mutex_lock(&mymutex1);
- printf("wait in mythread2.\n");
- pthread_cond_wait(&mycond,&mymutex1);
- pthread_mutex_unlock(&mymutex1);
- printf("end mythread2.\n");
- return NULL;
- }
- int main(void)
- {
- printf("begin main thread.\n");
- int i;
- pthread_t tid1,tid2;
- pthread_create(&tid1,NULL,mythread1,NULL);
- pthread_create(&tid2,NULL,mythread2,NULL);
- sleep(2);
- printf("try to wake up mythread1 and mythread2 in main thread.\n");
- if(pthread_cond_broadcast(&mycond)){
- printf("error\n");
- return 1;
- }
- void *res;
- pthread_join(tid1, &res);
- pthread_join(tid2, &res);
- printf("end main thread.\n");
- return 0;
- }
$ gcc threadTest.c -o test.exe
123@xyy ~/gcc-test
$ ./test.exe
begin main thread.
begin mythread1.
wait in mythread1.
begin mythread2.
wait in mythread2.
try to wake up mythread1 and mythread2 in main thread.
end mythread1.
end mythread1.
end main thread.
结束!
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