Setting N I/O threads should mean N-1 additional + 1 main thread.

src/networking.c

@@ -2658,9 +2658,9 @@ int io_threads_active;  /* Are the threads currently spinning waiting I/O? */
 int io_threads_op;      /* IO_THREADS_OP_WRITE or IO_THREADS_OP_READ. */
 
 /* This is the list of clients each thread will serve when threaded I/O is
- * used. We spawn N threads, and the N+1 list is used for the clients that
- * are processed by the main thread itself (this is why ther is "+1"). */
-list *io_threads_list[IO_THREADS_MAX_NUM+1];
+ * used. We spawn io_threads_num-1 threads, since one is the main thread
+ * itself. */
+list *io_threads_list[IO_THREADS_MAX_NUM];
 
 void *IOThreadMain(void *myid) {
     /* The ID is the thread number (from 0 to server.iothreads_num-1), and is
@@ -2720,12 +2720,16 @@ void initThreadedIO(void) {
         exit(1);
     }
 
-    /* Spawn the I/O threads. */
+    /* Spawn and initialize the I/O threads. */
     for (int i = 0; i < server.io_threads_num; i++) {
+        /* Things we do for all the threads including the main thread. */
+        io_threads_list[i] = listCreate();
+        if (i == 0) continue; /* Thread 0 is the main thread. */
+
+        /* Things we do only for the additional threads. */
         pthread_t tid;
         pthread_mutex_init(&io_threads_mutex[i],NULL);
         io_threads_pending[i] = 0;
-        io_threads_list[i] = listCreate();
         pthread_mutex_lock(&io_threads_mutex[i]); /* Thread will be stopped. */
         if (pthread_create(&tid,NULL,IOThreadMain,(void*)(long)i) != 0) {
             serverLog(LL_WARNING,"Fatal: Can't initialize IO thread.");
@@ -2733,14 +2737,13 @@ void initThreadedIO(void) {
         }
         io_threads[i] = tid;
     }
-    io_threads_list[server.io_threads_num] = listCreate(); /* For main thread */
 }
 
 void startThreadedIO(void) {
     if (tio_debug) { printf("S"); fflush(stdout); }
     if (tio_debug) printf("--- STARTING THREADED IO ---\n");
     serverAssert(io_threads_active == 0);
-    for (int j = 0; j < server.io_threads_num; j++)
+    for (int j = 1; j < server.io_threads_num; j++)
         pthread_mutex_unlock(&io_threads_mutex[j]);
     io_threads_active = 1;
 }
@@ -2754,7 +2757,7 @@ void stopThreadedIO(void) {
         (int) listLength(server.clients_pending_read),
         (int) listLength(server.clients_pending_write));
     serverAssert(io_threads_active == 1);
-    for (int j = 0; j < server.io_threads_num; j++)
+    for (int j = 1; j < server.io_threads_num; j++)
         pthread_mutex_lock(&io_threads_mutex[j]);
     io_threads_active = 0;
 }
@@ -2805,7 +2808,7 @@ int handleClientsWithPendingWritesUsingThreads(void) {
     while((ln = listNext(&li))) {
         client *c = listNodeValue(ln);
         c->flags &= ~CLIENT_PENDING_WRITE;
-        int target_id = item_id % (server.io_threads_num+1);
+        int target_id = item_id % server.io_threads_num;
         listAddNodeTail(io_threads_list[target_id],c);
         item_id++;
     }
@@ -2813,23 +2816,23 @@ int handleClientsWithPendingWritesUsingThreads(void) {
     /* Give the start condition to the waiting threads, by setting the
      * start condition atomic var. */
     io_threads_op = IO_THREADS_OP_WRITE;
-    for (int j = 0; j < server.io_threads_num; j++) {
+    for (int j = 1; j < server.io_threads_num; j++) {
         int count = listLength(io_threads_list[j]);
         io_threads_pending[j] = count;
     }
 
-    /* Also use the main thread to process a slide of clients. */
-    listRewind(io_threads_list[server.io_threads_num],&li);
+    /* Also use the main thread to process a slice of clients. */
+    listRewind(io_threads_list[0],&li);
     while((ln = listNext(&li))) {
         client *c = listNodeValue(ln);
         writeToClient(c,0);
     }
-    listEmpty(io_threads_list[server.io_threads_num]);
+    listEmpty(io_threads_list[0]);
 
-    /* Wait for all threads to end their work. */
+    /* Wait for all the other threads to end their work. */
     while(1) {
         unsigned long pending = 0;
-        for (int j = 0; j < server.io_threads_num; j++)
+        for (int j = 1; j < server.io_threads_num; j++)
             pending += io_threads_pending[j];
         if (pending == 0) break;
     }
@@ -2890,7 +2893,7 @@ int handleClientsWithPendingReadsUsingThreads(void) {
     int item_id = 0;
     while((ln = listNext(&li))) {
         client *c = listNodeValue(ln);
-        int target_id = item_id % (server.io_threads_num+1);
+        int target_id = item_id % server.io_threads_num;
         listAddNodeTail(io_threads_list[target_id],c);
         item_id++;
     }
@@ -2898,23 +2901,23 @@ int handleClientsWithPendingReadsUsingThreads(void) {
     /* Give the start condition to the waiting threads, by setting the
      * start condition atomic var. */
     io_threads_op = IO_THREADS_OP_READ;
-    for (int j = 0; j < server.io_threads_num; j++) {
+    for (int j = 1; j < server.io_threads_num; j++) {
         int count = listLength(io_threads_list[j]);
         io_threads_pending[j] = count;
     }
 
-    /* Also use the main thread to process a slide of clients. */
-    listRewind(io_threads_list[server.io_threads_num],&li);
+    /* Also use the main thread to process a slice of clients. */
+    listRewind(io_threads_list[0],&li);
     while((ln = listNext(&li))) {
         client *c = listNodeValue(ln);
         readQueryFromClient(c->conn);
     }
-    listEmpty(io_threads_list[server.io_threads_num]);
+    listEmpty(io_threads_list[0]);
 
-    /* Wait for all threads to end their work. */
+    /* Wait for all the other threads to end their work. */
     while(1) {
         unsigned long pending = 0;
-        for (int j = 0; j < server.io_threads_num; j++)
+        for (int j = 1; j < server.io_threads_num; j++)
             pending += io_threads_pending[j];
         if (pending == 0) break;
     }