try to fix race condition

src/ipc.m

@@ -35,6 +35,8 @@ const ev_tstamp IPC_TIMEOUT_INFINITY = 365*86400*100.0;
 
 struct ipc_channel {
 	struct rlist readers, writers;
+	unsigned creaders;
+	unsigned cwriters;
 	unsigned size;
 	unsigned beg;
 	unsigned count;
@@ -73,6 +75,8 @@ void
 ipc_channel_init(struct ipc_channel *ch)
 {
 	ch->beg = ch->count = 0;
+	ch->creaders = 0;
+	ch->cwriters = 0;
 	rlist_init(&ch->readers);
 	rlist_init(&ch->writers);
 }
@@ -96,12 +100,13 @@ void *
 ipc_channel_get_timeout(struct ipc_channel *ch, ev_tstamp timeout)
 {
 	/* channel is empty */
-	if (!ch->count) {
+	if (ch->count == 0 || ch->creaders >= ch->count) {
 		rlist_add_tail_entry(&ch->readers, fiber, state);
+		ch->creaders++;
 		bool cancellable = fiber_setcancellable(true);
-
 		bool timed_out = fiber_yield_timeout(timeout);
 		rlist_del_entry(fiber, state);
+		ch->creaders--;
 
 		fiber_testcancel();
 		fiber_setcancellable(cancellable);
@@ -115,6 +120,7 @@ ipc_channel_get_timeout(struct ipc_channel *ch, ev_tstamp timeout)
 		}
 	}
 
+	assert(ch->count > 0);
 	void *res = ch->item[ch->beg];
 	if (++ch->beg >= ch->size)
 		ch->beg -= ch->size;
@@ -127,6 +133,7 @@ ipc_channel_get_timeout(struct ipc_channel *ch, ev_tstamp timeout)
 		fiber_wakeup(f);
 	}
 
+
 	return res;
 }
 
@@ -141,13 +148,15 @@ ipc_channel_put_timeout(struct ipc_channel *ch, void *data,
 			ev_tstamp timeout)
 {
 	/* channel is full */
-	if (ch->count >= ch->size) {
+	if (ch->count >= ch->size || ch->cwriters >= ch->size - ch->count) {
 
 		rlist_add_tail_entry(&ch->writers, fiber, state);
+		ch->cwriters++;
 
 		bool cancellable = fiber_setcancellable(true);
 		bool timed_out = fiber_yield_timeout(timeout);
 		rlist_del_entry(fiber, state);
+		ch->cwriters--;
 
 		fiber_testcancel();
 		fiber_setcancellable(cancellable);
@@ -156,9 +165,10 @@ ipc_channel_put_timeout(struct ipc_channel *ch, void *data,
 			errno = ETIMEDOUT;
 			return -1;
 		}
-
 	}
 
+	assert(ch->count < ch->size);
+
 	unsigned i = ch->beg;
 	i += ch->count;
 	ch->count++;