redis源码笔记
作者在bio.c的头注释中对设计进行了详细的介绍/* Background I/O service for Redis.
这个文件是redis后台IO服务的实现
*
* This file implements operations that we need to perform in the background.
* Currently there is only a single operation, that is a background close(2)
* system call. This is needed as when the process is the last owner of a
* reference to a file closing it means unlinking it, and the deletion of the
* file is slow, blocking the server.
这个文件负责我们需要在后台执行的操作。现在redis的版本中只有一类的操作，后台的close 系统调用。
为了避免一个文件最后的owner在执行close操作带来的unlink使得阻塞server，将这类操作用单独的后台线程来执行
*
* In the future we'll either continue implementing new things we need or
* we'll switch to libeio. However there are probably long term uses for this
* file as we may want to put here Redis specific background tasks (for instance
* it is not impossible that we'll need a non blocking FLUSHDB/FLUSHALL
* implementation).
*
* DESIGN
* ------
*
* The design is trivial, we have a structure representing a job to perform
* and a different thread and job queue for every job type.
* Every thread wait for new jobs in its queue, and process every job
* sequentially.
每种作业类型一个queue。每个线程在它的queue里等待新的job到来。并且按照FIFO的顺序处理作业。
*
* Jobs of the same type are guaranteed to be processed from the least
* recently inserted to the most recently inserted (older jobs processed
* first).
*
* Currently there is no way for the creator of the job to be notified about
* the completion of the operation, this will only be added when/if needed.
作业完成后，其creator无法得到通知。
*/
现在的两类作业类型：1.close 2.aof_fsync
/* Background job opcodes */
#define REDIS_BIO_CLOSE_FILE 0 /* Deferred close(2) syscall. */
#define REDIS_BIO_AOF_FSYNC 1 /* Deferred AOF fsync. */
1 #include "redis.h"
2 #include "bio.h"
3
//使用互斥量+条件变量，作为线程的保护条件
4 static pthread_mutex_t bio_mutex;
5 static pthread_cond_t bio_condvar;
//两类作业的队列
6 static list *bio_jobs;
7 /* The following array is used to hold the number of pending jobs for every
8* OP type. This allows us to export the bioPendingJobsOfType() API that is
9* useful when the main thread wants to perform some operation that may involve
10* objects shared with the background thread. The main thread will just wait
11* that there are no longer jobs of this type to be executed before performing
12* the sensible operation. This data is also useful for reporting. */
13 static unsigned long long bio_pending;
14
15 /* This structure represents a background Job. It is only used locally to this
16* file as the API deos not expose the internals at all. */
17 struct bio_job {
18 time_t time; /* Time at which the job was created. */
19 /* Job specific arguments pointers. If we need to pass more than three
20 * arguments we can just pass a pointer to a structure or alike. */
21 void *arg1, *arg2, *arg3;
22 };
23
24 void *bioProcessBackgroundJobs(void *arg);
25
26 /* Make sure we have enough stack to perform all the things we do in the
27* main thread. */
28 #define REDIS_THREAD_STACK_SIZE (1024*1024*4)
29
30 /* Initialize the background system, spawning the thread. */
31 void bioInit(void) {
32 pthread_attr_t attr;
33 pthread_t thread;
34 size_t stacksize;
35 int j;
36
37 /* Initialization of state vars and objects */
38 for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
39 pthread_mutex_init(&bio_mutex,NULL);
40 pthread_cond_init(&bio_condvar,NULL);
41 bio_jobs = listCreate();
42 bio_pending = 0;
43 }
44
45 /* Set the stack size as by default it may be small in some system */
46 pthread_attr_init(&attr);
47 pthread_attr_getstacksize(&attr,&stacksize);
48 if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */
49 while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
50 pthread_attr_setstacksize(&attr, stacksize);
51
52 /* Ready to spawn our threads. We use the single argument the thread
53 * function accepts in order to pass the job ID the thread is
54 * responsible of. */
55 for (j = 0; j < REDIS_BIO_NUM_OPS; j++) {
56 void *arg = (void*)(unsigned long) j;
57 if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
58 redisLog(REDIS_WARNING,"Fatal: Can't initialize Background Jobs.");
59 exit(1);
60 }
61 }
62 }
63
64 void bioCreateBackgroundJob(int type, void *arg1, void *arg2, void *arg3) {
65 struct bio_job *job = zmalloc(sizeof(*job));
66
67 job->time = time(NULL);
68 job->arg1 = arg1;
69 job->arg2 = arg2;
70 job->arg3 = arg3;
71 pthread_mutex_lock(&bio_mutex);
72 listAddNodeTail(bio_jobs,job);
73 bio_pending++;
74 pthread_cond_signal(&bio_condvar);
75 pthread_mutex_unlock(&bio_mutex);
76 }
77
78 void *bioProcessBackgroundJobs(void *arg) {
79 struct bio_job *job;
80 unsigned long type = (unsigned long) arg;
81
82 pthread_detach(pthread_self());
83 pthread_mutex_lock(&bio_mutex);
84 while(1) {
85 listNode *ln;
86
87 /* The loop always starts with the lock hold. */
88 if (listLength(bio_jobs) == 0) {
89 pthread_cond_wait(&bio_condvar,&bio_mutex);
90 continue;
91 }
92 /* Pop the job from the queue. */
93 ln = listFirst(bio_jobs);
94 job = ln->value;
95 /* It is now possible to unlock the background system as we know have
96 * a stand alone job structure to process.*/
97 pthread_mutex_unlock(&bio_mutex);
98
99 /* Process the job accordingly to its type. */
100 if (type == REDIS_BIO_CLOSE_FILE) {
101 close((long)job->arg1);
102 } else if (type == REDIS_BIO_AOF_FSYNC) {
103 aof_fsync((long)job->arg1);
104 } else {
105 redisPanic("Wrong job type in bioProcessBackgroundJobs().");
106 }
107 zfree(job);
108
109 /* Lock again before reiterating the loop, if there are no longer
110 * jobs to process we'll block again in pthread_cond_wait(). */
111 pthread_mutex_lock(&bio_mutex);
112 listDelNode(bio_jobs,ln);
113 bio_pending--;
114 }
115 }
116
117 /* Return the number of pending jobs of the specified type. */
118 unsigned long long bioPendingJobsOfType(int type) {
119 unsigned long long val;
120 pthread_mutex_lock(&bio_mutex);
121 val = bio_pending;
122 pthread_mutex_unlock(&bio_mutex);
123 return val;
124 }
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