Background I/O library enhanced so that the main thread can query for the number of pending jobs of the specified type.

src/bio.c

@@ -27,6 +27,13 @@
 static pthread_mutex_t bio_mutex;
 static pthread_cond_t bio_condvar;
 static list *bio_jobs;
+/* The following array is used to hold the number of pending jobs for every
+ * OP type. This allows us to export the bioPendingJobsOfType() API that is
+ * useful when the main thread wants to perform some operation that may involve
+ * objects shared with the background thread. The main thread will just wait
+ * that there are no longer jobs of this type to be executed before performing
+ * the sensible operation. This data is also useful for reporting. */
+static unsigned long long *bio_pending;
 
 /* This structure represents a background Job. It is only used locally to this
  * file as the API deos not expose the internals at all. */
@@ -46,10 +53,14 @@ void bioInit(void) {
     pthread_attr_t attr;
     pthread_t thread;
     size_t stacksize;
+    int j;
 
+    /* Initialization of state vars and objects */
     pthread_mutex_init(&bio_mutex,NULL);
     pthread_cond_init(&bio_condvar,NULL);
     bio_jobs = listCreate();
+    bio_pending = zmalloc(sizeof(*bio_pending)*REDIS_BIO_MAX_OP_ID);
+    for (j = 0; j < REDIS_BIO_MAX_OP_ID; j++) bio_pending[j] = 0;
 
     /* Set the stack size as by default it may be small in some system */
     pthread_attr_init(&attr);
@@ -72,6 +83,7 @@ void bioCreateBackgroundJob(int type, void *data) {
     job->data = data;
     pthread_mutex_lock(&bio_mutex);
     listAddNodeTail(bio_jobs,job);
+    bio_pending[type]++;
     pthread_cond_signal(&bio_condvar);
     pthread_mutex_unlock(&bio_mutex);
 }
@@ -84,6 +96,7 @@ void *bioProcessBackgroundJobs(void *arg) {
     pthread_mutex_lock(&bio_mutex);
     while(1) {
         listNode *ln;
+        int type;
 
         /* The loop always starts with the lock hold. */
         if (listLength(bio_jobs) == 0) {
@@ -93,13 +106,14 @@ void *bioProcessBackgroundJobs(void *arg) {
         /* Pop the job from the queue. */
         ln = listFirst(bio_jobs);
         job = ln->value;
+        type = job->type;
         listDelNode(bio_jobs,ln);
         /* 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);
 
         /* Process the job accordingly to its type. */
-        if (job->type == REDIS_BIO_CLOSE_FILE) {
+        if (type == REDIS_BIO_CLOSE_FILE) {
             close((long)job->data);
         } else {
             redisPanic("Wrong job type in bioProcessBackgroundJobs().");
@@ -109,5 +123,36 @@ void *bioProcessBackgroundJobs(void *arg) {
         /* 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);
+        bio_pending[type]--;
+    }
+}
+
+/* Return the number of pending jobs of the specified type. */
+unsigned long long bioPendingJobsOfType(int type) {
+    unsigned long long val;
+    pthread_mutex_lock(&bio_mutex);
+    val = bio_pending[type];
+    pthread_mutex_unlock(&bio_mutex);
+    return val;
+}
+
+/* Wait until the number of pending jobs of the specified type are
+ * less or equal to the specified number.
+ *
+ * This function may block for long time, it should only be used to perform
+ * special tasks like AOF rewriting or alike. */
+void bioWaitPendingJobsLE(int type, unsigned long long num) {
+    unsigned long long iteration = 0;
+
+    /* We poll the jobs queue aggressively to start, and gradually relax
+     * the polling speed if it is going to take too much time. */
+    while(1) {
+        iteration++;
+        if (iteration > 1000 && iteration <= 10000) {
+            usleep(100);
+        } else if (iteration > 10000) {
+            usleep(1000);
+        }
+        if (bioPendingJobsOfType(type) <= num) break;
     }
 }

src/bio.h

@@ -1,6 +1,11 @@
 /* Exported API */
 void bioInit(void);
 void bioCreateBackgroundJob(int type, void *data);
+unsigned long long bioPendingJobsOfType(int type);
+void bioWaitPendingJobsLE(int type, unsigned long long num);
 
 /* Background job opcodes */
-#define REDIS_BIO_CLOSE_FILE    1
+#define REDIS_BIO_ZERO_OP_ID    0 /* We don't use zero as it is the most likely
+                                   * passed value in case of bugs/races. */
+#define REDIS_BIO_CLOSE_FILE    1 /* Deferred close(2) syscall. */
+#define REDIS_BIO_MAX_OP_ID     1