Redis的模块化开发设计的还是相当不错的，在Bio.h和Bio.c文件中定义了一个多线程的文件任务处理模块，在添加和处理任务的时候使用互斥锁和条件变量进行的同步，而且本身也支持多线程，这个模块的支持两个类型，一个是关闭文件，另一个是将内存中的数据刷新到磁盘中去，也算是数据持久化的一部分了。其中三个宏定义了这些数据。
#define REDIS_BIO_CLOSE_FILE 0 /*关闭一个系统调用*/
#define REDIS_BIO_AOF_FSYNC 1 /*文件数据刷新到磁盘*/
#define REDIS_BIO_NUM_OPS 2/*支持任务类型数*/
模块的基础变量数据：
static pthread_t bio_threads[REDIS_BIO_NUM_OPS];/*多线程情况下线程的个数*/
static pthread_mutex_t bio_mutex[REDIS_BIO_NUM_OPS];/*互斥锁*/
static pthread_cond_t bio_condvar[REDIS_BIO_NUM_OPS];/*条件变量*/
static list *bio_jobs[REDIS_BIO_NUM_OPS];/*后台任务链表，每个线程一个，根据下标区分*/
static unsigned long long bio_pending[REDIS_BIO_NUM_OPS];/*记录每个线程剩余的任务数*/
struct bio_job
{/*后台IO节点，任务是通过链表来维护的，这个算是链表内的节点数据，第一个是创建时间，第二个是指定参数。*/
time_t time; /* Time at which the job was created. */
/* Job specific arguments pointers. If we need to pass more than three
* arguments we can just pass a pointer to a structure or alike. */
void *arg1, *arg2, *arg3;
};
具体的实现接口，注意，这个模块中.h和.c文件中定义的接口不一样，不知道是写错了还是怎么回事，.h中定义的部分接口没有实现：
void bioInit(void); /初始化变量数据和线程数据/
void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3);/*添加一个任务*/void *bioProcessBackgroundJobs(void *arg);/*处理指定的任务数组*/
unsigned long long bioPendingJobsOfType(int type);/*获取剩余的任务数*/
void bioKillThreads(void);/*关闭线程*/
1.void bioInit(void);
void bioInit(void)
{
pthread_attr_t attr;
pthread_t thread;
size_t stacksize;
int j; /*初始化条件变量和互斥锁*/
for (j = ; j < REDIS_BIO_NUM_OPS; j++)
{
pthread_mutex_init(&bio_mutex[j],NULL);
pthread_cond_init(&bio_condvar[j],NULL);
bio_jobs[j] = listCreate();
bio_pending[j] = ;
} /*初始化线程属性，自动增加线程栈的大小*/
pthread_attr_init(&attr);
pthread_attr_getstacksize(&attr,&stacksize);
if (!stacksize) stacksize = ; /* The world is full of Solaris Fixes */
while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= ;
pthread_attr_setstacksize(&attr, stacksize); /* Ready to spawn our threads. We use the single argument the thread
* function accepts in order to pass the job ID the thread is
* responsible of. */
for (j = ; j < REDIS_BIO_NUM_OPS; j++)
{
void *arg = (void*)(unsigned long) j;
if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != )
{
redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");
exit();
}
bio_threads[j] = thread;
}
}//这个没啥可说的，无非是初始化同步的数据和线程数据
void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3);/*添加一个任务*/
/*创建一个后台任务，创建任务支持多线程
添加事件和处理事件就像是消费者和生产者的问题一样，采用互斥和条件变量来控制
参数1是添加到哪个队列中，剩余是三个参数*/
void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3)
{
struct bio_job *job = zmalloc(sizeof(*job)); job->time = time(NULL);
job->arg1 = arg1;
job->arg2 = arg2;
job->arg3 = arg3;
/*添加的时候要注意并发问题，添加完了发个信号*/
pthread_mutex_lock(&bio_mutex[type]);
listAddNodeTail(bio_jobs[type],job);
bio_pending[type]++;
pthread_cond_signal(&bio_condvar[type]);
pthread_mutex_unlock(&bio_mutex[type]);
}
void *bioProcessBackgroundJobs(void *arg);
/*事件消费函数*/
void *bioProcessBackgroundJobs(void *arg)
{
struct bio_job *job;
unsigned long type = (unsigned long) arg;
sigset_t sigset; /* Make the thread killable at any time, so that bioKillThreads()
* can work reliably. */
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);/*设置线程为收到cancle信号马上退出*/
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL); pthread_mutex_lock(&bio_mutex[type]);
/* Block SIGALRM so we are sure that only the main thread will
* receive the watchdog signal. */
sigemptyset(&sigset);
sigaddset(&sigset, SIGALRM);
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
redisLog(REDIS_WARNING,
"Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno)); while()
{
listNode *ln; /* The loop always starts with the lock hold. */
if (listLength(bio_jobs[type]) == )
{
pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
continue;
}
/* Pop the job from the queue. */
ln = listFirst(bio_jobs[type]);
job = ln->value;
/* It is now possible to unlock the background system as we know have
* a stand alone job structure to process.*/
pthread_mutex_unlock(&bio_mutex[type]);
/*处理任务的时候解除互斥锁，提高效率*/
/* 区分任务类型，具体执行 */
if (type == REDIS_BIO_CLOSE_FILE)
{
close((long)job->arg1);
}
else if (type == REDIS_BIO_AOF_FSYNC)
{
aof_fsync((long)job->arg1);
}
else
{
redisPanic("Wrong job type in bioProcessBackgroundJobs().");
}
zfree(job); /* Lock again before reiterating the loop, if there are no longer
* jobs to process we'll block again in pthread_cond_wait(). */
pthread_mutex_lock(&bio_mutex[type]);/*修改公共资源的的是要加锁发，防止并发问题*/
listDelNode(bio_jobs[type],ln);/*删除节点，并减掉任务数*/
bio_pending[type]--;
}
}
void bioKillThreads(void);/*关闭线程*/
void bioKillThreads(void)
{
int err, j; for (j = ; j < REDIS_BIO_NUM_OPS; j++)
{
if (pthread_cancel(bio_threads[j]) == ) /*给线程发送结束信号，发送成功之后等待其结束*/
{
if ((err = pthread_join(bio_threads[j],NULL)) != )
{
redisLog(REDIS_WARNING,"Bio thread for job type #%d can be joined: %s",j, strerror(err));
}
else
{
redisLog(REDIS_WARNING,"Bio thread for job type #%d terminated",j);
}
}
}
}
这个后台任务值负责关闭系统的调用和数据的持久化。