我正在寻找使用pthread同步语义在C中推荐的线程安全阻塞队列（多生产者/消费者）的实现。
答案 0 :(得分：27)
这是我使用的
threadqueue.h
#ifndef _THREADQUEUE_H_
#define _THREADQUEUE_H_ 1
#include <pthread.h>
#ifdef __cplusplus
extern "C" {
#endif
/**
* @defgroup ThreadQueue ThreadQueue
*
* Little API for waitable queues, typically used for passing messages
* between threads.
*
*/
/**
* @mainpage
*/
/**
* A thread message.
*
* @ingroup ThreadQueue
*
* This is used for passing to #thread_queue_get for retreive messages.
* the date is stored in the data member, the message type in the #msgtype.
*
* Typical:
* @code
* struct threadmsg;
* struct myfoo *foo;
* while(1)
* ret = thread_queue_get(&queue,NULL,&message);
* ..
* foo = msg.data;
* switch(msg.msgtype){
* ...
* }
* }
* @endcode
*
*/
struct threadmsg{
/**
* Holds the data.
*/
void *data;
/**
* Holds the messagetype
*/
long msgtype;
/**
* Holds the current queue lenght. Might not be meaningful if there's several readers
*/
long qlength;
};
/**
* A TthreadQueue
*
* @ingroup ThreadQueue
*
* You should threat this struct as opaque, never ever set/get any
* of the variables. You have been warned.
*/
struct threadqueue {
/**
* Length of the queue, never set this, never read this.
* Use #threadqueue_length to read it.
*/
long length;
/**
* Mutex for the queue, never touch.
*/
pthread_mutex_t mutex;
/**
* Condition variable for the queue, never touch.
*/
pthread_cond_t cond;
/**
* Internal pointers for the queue, never touch.
*/
struct msglist *first,*last;
/**
* Internal cache of msglists
*/
struct msglist *msgpool;
/**
* No. of elements in the msgpool
*/
long msgpool_length;
};
/**
* Initializes a queue.
*
* @ingroup ThreadQueue
*
* thread_queue_init initializes a new threadqueue. A new queue must always
* be initialized before it is used.
*
* @param queue Pointer to the queue that should be initialized
* @return 0 on success see pthread_mutex_init
*/
int thread_queue_init(struct threadqueue *queue);
/**
* Adds a message to a queue
*
* @ingroup ThreadQueue
*
* thread_queue_add adds a "message" to the specified queue, a message
* is just a pointer to a anything of the users choice. Nothing is copied
* so the user must keep track on (de)allocation of the data.
* A message type is also specified, it is not used for anything else than
* given back when a message is retreived from the queue.
*
* @param queue Pointer to the queue on where the message should be added.
* @param data the "message".
* @param msgtype a long specifying the message type, choice of the user.
* @return 0 on succes ENOMEM if out of memory EINVAL if queue is NULL
*/
int thread_queue_add(struct threadqueue *queue, void *data, long msgtype);
/**
* Gets a message from a queue
*
* @ingroup ThreadQueue
*
* thread_queue_get gets a message from the specified queue, it will block
* the caling thread untill a message arrives, or the (optional) timeout occurs.
* If timeout is NULL, there will be no timeout, and thread_queue_get will wait
* untill a message arrives.
*
* struct timespec is defined as:
* @code
* struct timespec {
* long tv_sec; // seconds
* long tv_nsec; // nanoseconds
* };
* @endcode
*
* @param queue Pointer to the queue to wait on for a message.
* @param timeout timeout on how long to wait on a message
* @param msg pointer that is filled in with mesagetype and data
*
* @return 0 on success EINVAL if queue is NULL ETIMEDOUT if timeout occurs
*/
int thread_queue_get(struct threadqueue *queue, const struct timespec *timeout, struct threadmsg *msg);
/**
* Gets the length of a queue
*
* @ingroup ThreadQueue
*
* threadqueue_length returns the number of messages waiting in the queue
*
* @param queue Pointer to the queue for which to get the length
* @return the length(number of pending messages) in the queue
*/
long thread_queue_length( struct threadqueue *queue );
/**
* @ingroup ThreadQueue
* Cleans up the queue.
*
* threadqueue_cleanup cleans up and destroys the queue.
* This will remove all messages from a queue, and reset it. If
* freedata is != 0 free(3) will be called on all pending messages in the queue
* You cannot call this if there are someone currently adding or getting messages
* from the queue.
* After a queue have been cleaned, it cannot be used again untill #thread_queue_init
* has been called on the queue.
*
* @param queue Pointer to the queue that should be cleaned
* @param freedata set to nonzero if free(3) should be called on remaining
* messages
* @return 0 on success EINVAL if queue is NULL EBUSY if someone is holding any locks on the queue
*/
int thread_queue_cleanup(struct threadqueue *queue, int freedata);
#ifdef __cplusplus
}
#endif
#endif
threadqueue.c
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <pthread.h>
#include <sys/time.h>
#include "../h/threadqueue.h"
#define MSGPOOL_SIZE 256
struct msglist {
struct threadmsg msg;
struct msglist *next;
};
static inline struct msglist *get_msglist(struct threadqueue *queue)
{
struct msglist *tmp;
if(queue->msgpool != NULL) {
tmp = queue->msgpool;
queue->msgpool = tmp->next;
queue->msgpool_length--;
} else {
tmp = malloc(sizeof *tmp);
}
return tmp;
}
static inline void release_msglist(struct threadqueue *queue,struct msglist *node)
{
if(queue->msgpool_length > ( queue->length/8 + MSGPOOL_SIZE)) {
free(node);
} else {
node->msg.data = NULL;
node->msg.msgtype = 0;
node->next = queue->msgpool;
queue->msgpool = node;
queue->msgpool_length++;
}
if(queue->msgpool_length > (queue->length/4 + MSGPOOL_SIZE*10)) {
struct msglist *tmp = queue->msgpool;
queue->msgpool = tmp->next;
free(tmp);
queue->msgpool_length--;
}
}
int thread_queue_init(struct threadqueue *queue)
{
int ret = 0;
if (queue == NULL) {
return EINVAL;
}
memset(queue, 0, sizeof(struct threadqueue));
ret = pthread_cond_init(&queue->cond, NULL);
if (ret != 0) {
return ret;
}
ret = pthread_mutex_init(&queue->mutex, NULL);
if (ret != 0) {
pthread_cond_destroy(&queue->cond);
return ret;
}
return 0;
}
int thread_queue_add(struct threadqueue *queue, void *data, long msgtype)
{
struct msglist *newmsg;
pthread_mutex_lock(&queue->mutex);
newmsg = get_msglist(queue);
if (newmsg == NULL) {
pthread_mutex_unlock(&queue->mutex);
return ENOMEM;
}
newmsg->msg.data = data;
newmsg->msg.msgtype = msgtype;
newmsg->next = NULL;
if (queue->last == NULL) {
queue->last = newmsg;
queue->first = newmsg;
} else {
queue->last->next = newmsg;
queue->last = newmsg;
}
if(queue->length == 0)
pthread_cond_broadcast(&queue->cond);
queue->length++;
pthread_mutex_unlock(&queue->mutex);
return 0;
}
int thread_queue_get(struct threadqueue *queue, const struct timespec *timeout, struct threadmsg *msg)
{
struct msglist *firstrec;
int ret = 0;
struct timespec abstimeout;
if (queue == NULL || msg == NULL) {
return EINVAL;
}
if (timeout) {
struct timeval now;
gettimeofday(&now, NULL);
abstimeout.tv_sec = now.tv_sec + timeout->tv_sec;
abstimeout.tv_nsec = (now.tv_usec * 1000) + timeout->tv_nsec;
if (abstimeout.tv_nsec >= 1000000000) {
abstimeout.tv_sec++;
abstimeout.tv_nsec -= 1000000000;
}
}
pthread_mutex_lock(&queue->mutex);
/* Will wait until awakened by a signal or broadcast */
while (queue->first == NULL && ret != ETIMEDOUT) { //Need to loop to handle spurious wakeups
if (timeout) {
ret = pthread_cond_timedwait(&queue->cond, &queue->mutex, &abstimeout);
} else {
pthread_cond_wait(&queue->cond, &queue->mutex);
}
}
if (ret == ETIMEDOUT) {
pthread_mutex_unlock(&queue->mutex);
return ret;
}
firstrec = queue->first;
queue->first = queue->first->next;
queue->length--;
if (queue->first == NULL) {
queue->last = NULL; // we know this since we hold the lock
queue->length = 0;
}
msg->data = firstrec->msg.data;
msg->msgtype = firstrec->msg.msgtype;
msg->qlength = queue->length;
release_msglist(queue,firstrec);
pthread_mutex_unlock(&queue->mutex);
return 0;
}
//maybe caller should supply a callback for cleaning the elements ?
int thread_queue_cleanup(struct threadqueue *queue, int freedata)
{
struct msglist *rec;
struct msglist *next;
struct msglist *recs[2];
int ret,i;
if (queue == NULL) {
return EINVAL;
}
pthread_mutex_lock(&queue->mutex);
recs[0] = queue->first;
recs[1] = queue->msgpool;
for(i = 0; i < 2 ; i++) {
rec = recs[i];
while (rec) {
next = rec->next;
if (freedata) {
free(rec->msg.data);
}
free(rec);
rec = next;
}
}
pthread_mutex_unlock(&queue->mutex);
ret = pthread_mutex_destroy(&queue->mutex);
pthread_cond_destroy(&queue->cond);
return ret;
}
long thread_queue_length(struct threadqueue *queue)
{
long counter;
// get the length properly
pthread_mutex_lock(&queue->mutex);
counter = queue->length;
pthread_mutex_unlock(&queue->mutex);
return counter;
}
答案 1 :(得分：5)
尝试APR队列。它由apache web服务器使用并经过充分测试。