thread 讲解 很经典的东西 POSIX的标准的

#include <stdio.h> #include <stdlib.h> #include "control.h" #include "queue.h" #include "dbug.h" /* the work_queue holds tasks for the various threads to complete. */ struct work_queue { data_control control; queue work; } wq; /* I added a job number to the work node. Normally, the work node would contain additional data that needed to be processed. */ typedef struct work_node { struct node *next; int jobnum; } wnode; /* the cleanup queue holds stopped threads. Before a thread terminates, it adds itself to this list. Since the main thread is waiting for changes in this list, it will then wake up and clean up the newly terminated thread. */ struct cleanup_queue { data_control control; queue cleanup; } cq; /* I added a thread number (for debugging/instructional purposes) and a thread id to the cleanup node. The cleanup node gets passed to the new thread on startup, and just before the thread stops, it attaches the cleanup node to the cleanup queue. The main thread monitors the cleanup queue and is the one that performs the necessary cleanup. */ typedef struct cleanup_node { struct node *next; int threadnum; pthread_t tid; } cnode; void *threadfunc(void *myarg) { wnode *mywork; cnode *mynode; mynode=(cnode *) myarg; pthread_mutex_lock(&wq.control.mutex); while (wq.control.active) { while (wq.work.head==NULL && wq.control.active) { pthread_cond_wait(&wq.control.cond, &wq.control.mutex); } if (!wq.control.active) break; //we got something! mywork=(wnode *) queue_get(&wq.work); pthread_mutex_unlock(&wq.control.mutex); //perform processing... printf("Thread number %d processing job %d\n",mynode->threadnum,mywork->jobnum); free(mywork); pthread_mutex_lock(&wq.control.mutex); } pthread_mutex_unlock(&wq.control.mutex); pthread_mutex_lock(&cq.control.mutex); queue_put(&cq.cleanup,(node *) mynode); pthread_mutex_unlock(&cq.control.mutex); pthread_cond_signal(&cq.control.cond); printf("thread %d shutting down...\n",mynode->threadnum); return NULL; } #define NUM_WORKERS 4 int numthreads; void join_threads(void) { cnode *curnode; printf("joining threads...\n"); while (numthreads) { pthread_mutex_lock(&cq.control.mutex); /* below, we sleep until there really is a new cleanup node. This takes care of any false wakeups... even if we break out of pthread_cond_wait(), we don't make any assumptions that the condition we were waiting for is true. */ while (cq.cleanup.head==NULL) { pthread_cond_wait(&cq.control.cond,&cq.control.mutex); } /* at this point, we hold the mutex and there is an item in the list that we need to process. First, we remove the node from the queue. Then, we call pthread_join() on the tid stored in the node. When pthread_join() returns, we have cleaned up after a thread. Only then do we free() the node, decrement the number of additional threads we need to wait for and repeat the entire process, if necessary */ curnode = (cnode *) queue_get(&cq.cleanup); pthread_mutex_unlock(&cq.control.mutex); pthread_join(curnode->tid,NULL); printf("joined with thread %d\n",curnode->threadnum); free(curnode); numthreads--; } } int create_threads(void) { int x; cnode *curnode; for (x=0; x<NUM_WORKERS; x++) { curnode=malloc(sizeof(cnode)); if (!curnode) return 1; curnode->threadnum=x; if (pthread_create(&curnode->tid, NULL, threadfunc, (void *) curnode)) return 1; printf("created thread %d\n",x); numthreads++; } return 0; } void initialize_structs(void) { numthreads=0; if (control_init(&wq.control)) dabort(); queue_init(&wq.work); if (control_init(&cq.control)) { control_destroy(&wq.control); dabort(); } queue_init(&wq.work); control_activate(&wq.control); } void cleanup_structs(void) { control_destroy(&cq.control); control_destroy(&wq.control); } int main(void) { int x; wnode *mywork; initialize_structs(); /* CREATION */ if (create_threads()) { printf("Error starting threads... cleaning up.\n"); join_threads(); dabort(); } pthread_mutex_lock(&wq.control.mutex); for (x=0; x<16000; x++) { mywork=malloc(sizeof(wnode)); if (!mywork) { printf("ouch! can't malloc!\n"); break; } mywork->jobnum=x; queue_put(&wq.work,(node *) mywork); } pthread_mutex_unlock(&wq.control.mutex); pthread_cond_broadcast(&wq.control.cond); printf("sleeping...\n"); sleep(2); printf("deactivating work queue...\n"); control_deactivate(&wq.control); /* CLEANUP */ join_threads(); cleanup_structs(); }