From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 25 Mar 2012 15:31:50 +0000 (+0100)
Subject: Fix race in ThreadsManager::sleep()
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=58c2fe391d869e417e568cd47eea77d46a408f9b;hp=c483ffc773c012b49f4ea2f5bd1d788c1f0dc4ac

Fix race in ThreadsManager::sleep()

We cannot set do_sleep flag of main thread before
"bestmove" is sent to GUI, otherwise GUI could send
immediately the next "go" command that triggers
start_thinking() and because do_sleep is set UI
thread resets the flag to launch a new search. But
when shortly after main thread returns to main_loop()
flag is incorrectly reset and main thread goes to sleep
hanging the engine.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/thread.cpp b/src/thread.cpp
index d67b9fcd..ab20d781 100644
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -227,7 +227,7 @@ void ThreadsManager::read_uci_options() {
 
 void ThreadsManager::wake_up() {
 
-  for (int i = 0; i < size(); i++)
+  for (int i = 1; i < size(); i++) // Main thread is already running
   {
       threads[i]->do_sleep = false;
 
@@ -237,12 +237,13 @@ void ThreadsManager::wake_up() {
 }
 
 
-// sleep() is called after the search to ask threads to wait on sleep condition
+// sleep() is called after the search to ask all the threads but the main to go
+// waiting on a sleep condition.
 
 void ThreadsManager::sleep() {
 
-  for (int i = 0; i < size(); i++)
-      threads[i]->do_sleep = true;
+  for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself
+      threads[i]->do_sleep = true; // to avoid a race with start_thinking()
 }