Fix stuck master thread in produce_socket() by always signalling sq_empty from the worker threads

mongoose.c

@@ -3970,29 +3970,25 @@ static int consume_socket(struct mg_context *ctx, struct socket *sp) {
   while (ctx->sq_head == ctx->sq_tail && ctx->stop_flag == 0) {
     pthread_cond_wait(&ctx->sq_full, &ctx->mutex);
   }
-  // Master thread could wake us up without putting a socket.
-  // If this happens, it is time to exit.
-  if (ctx->stop_flag) {
-    (void) pthread_mutex_unlock(&ctx->mutex);
-    return 0;
-  }
-  assert(ctx->sq_head > ctx->sq_tail);
-
-  // Copy socket from the queue and increment tail
-  *sp = ctx->queue[ctx->sq_tail % ARRAY_SIZE(ctx->queue)];
-  ctx->sq_tail++;
-  DEBUG_TRACE(("grabbed socket %d, going busy", sp->sock));
 
-  // Wrap pointers if needed
-  while (ctx->sq_tail > (int) ARRAY_SIZE(ctx->queue)) {
-    ctx->sq_tail -= ARRAY_SIZE(ctx->queue);
-    ctx->sq_head -= ARRAY_SIZE(ctx->queue);
+  // If we're stopping, sq_head may be equal to sq_tail.
+  if (ctx->sq_head > ctx->sq_tail) {
+    // Copy socket from the queue and increment tail
+    *sp = ctx->queue[ctx->sq_tail % ARRAY_SIZE(ctx->queue)];
+    ctx->sq_tail++;
+    DEBUG_TRACE(("grabbed socket %d, going busy", sp->sock));
+
+    // Wrap pointers if needed
+    while (ctx->sq_tail > (int) ARRAY_SIZE(ctx->queue)) {
+      ctx->sq_tail -= ARRAY_SIZE(ctx->queue);
+      ctx->sq_head -= ARRAY_SIZE(ctx->queue);
+    }
   }
 
   (void) pthread_cond_signal(&ctx->sq_empty);
   (void) pthread_mutex_unlock(&ctx->mutex);
 
-  return 1;
+  return !ctx->stop_flag;
 }
 
 static void worker_thread(struct mg_context *ctx) {
@@ -4004,7 +4000,9 @@ static void worker_thread(struct mg_context *ctx) {
   conn->buf = (char *) (conn + 1);
   assert(conn != NULL);
 
-  while (ctx->stop_flag == 0 && consume_socket(ctx, &conn->client)) {
+  // Call consume_socket() even when ctx->stop_flag > 0, to let it signal
+  // sq_empty condvar to wake up the master waiting in produce_socket()
+  while (consume_socket(ctx, &conn->client)) {
     conn->birth_time = time(NULL);
     conn->ctx = ctx;
 
@@ -4041,15 +4039,17 @@ static void produce_socket(struct mg_context *ctx, const struct socket *sp) {
   (void) pthread_mutex_lock(&ctx->mutex);
 
   // If the queue is full, wait
-  while (ctx->sq_head - ctx->sq_tail >= (int) ARRAY_SIZE(ctx->queue)) {
+  while (ctx->stop_flag == 0 &&
+         ctx->sq_head - ctx->sq_tail >= (int) ARRAY_SIZE(ctx->queue)) {
     (void) pthread_cond_wait(&ctx->sq_empty, &ctx->mutex);
   }
-  assert(ctx->sq_head - ctx->sq_tail < (int) ARRAY_SIZE(ctx->queue));
 
-  // Copy socket to the queue and increment head
-  ctx->queue[ctx->sq_head % ARRAY_SIZE(ctx->queue)] = *sp;
-  ctx->sq_head++;
-  DEBUG_TRACE(("queued socket %d", sp->sock));
+  if (ctx->sq_head - ctx->sq_tail < (int) ARRAY_SIZE(ctx->queue)) {
+    // Copy socket to the queue and increment head
+    ctx->queue[ctx->sq_head % ARRAY_SIZE(ctx->queue)] = *sp;
+    ctx->sq_head++;
+    DEBUG_TRACE(("queued socket %d", sp->sock));
+  }
 
   (void) pthread_cond_signal(&ctx->sq_full);
   (void) pthread_mutex_unlock(&ctx->mutex);
@@ -4106,7 +4106,7 @@ static void master_thread(struct mg_context *ctx) {
 #endif // _WIN32
     } else {
       for (sp = ctx->listening_sockets; sp != NULL; sp = sp->next) {
-        if (FD_ISSET(sp->sock, &read_set)) {
+        if (ctx->stop_flag == 0 && FD_ISSET(sp->sock, &read_set)) {
           accept_new_connection(sp, ctx);
         }
       }