cpp/openttd-patchpack/source Changeset - r25711:31eedcf7ade0

Changeset - r25711:31eedcf7ade0

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Patric Stout - 3 years ago 2021-06-17 18:10:40
truebrain@openttd.org

Fix: on startup, NewGRF scan could case race-condition (#9382)

Creating a thread was not thread-safe. The irony.

The video-driver has a function GameLoopPause() which first checks
if the thread is the game-thread or not. For this it needs access
to this->game_thread. This variable is set in StartNewThread().

However, due to timing, it is well possible GameLoopPause() is
called from the thread well before this->game_thread is assigned.

And so we have a race-condition!

Simply solve this by preventing a thread to start till we are
done with our bookkeeping.

1 file changed with 11 insertions and 0 deletions:

src/thread.h

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src/thread.h

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@@ @@ -14,6 +14,7 @@ @@
 #include "crashlog.h"
 #include <system_error>
 #include <thread>
 #include <mutex>
 /**
  * Sleep on the current thread for a defined time.
@@ @@ -46,7 +47,17 @@ inline bool StartNewThread(std::thread * @@
+{
 #ifndef NO_THREADS
 	try {
 		static std::mutex thread_startup_mutex;
 		std::lock_guard<std::mutex> lock(thread_startup_mutex);
 		std::thread t([] (const char *name, TFn&& F, TArgs&&... A) {
 				/* Delay starting the thread till the main thread is finished
 				 * with the administration. This prevent race-conditions on
 				 * startup. */
+				{
 					std::lock_guard<std::mutex> lock(thread_startup_mutex);
+				}
 				SetCurrentThreadName(name);
 				CrashLog::InitThread();
 				try {

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