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Fixed a race condition between the Watcher thread and ThreadLocal

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A race condition exist between the Watcher thread and main(). A case was found where the Watcher thread does not get execution time before the main function returns and calls atexit(). At that point the Watcher thread started runing tls_init() code while the main thread was shutting down. This resulted in rare crashes and deadlocks.
This commit is contained in:
cgyrling 2024-03-18 15:00:04 -07:00 committed by GitHub
parent eff443c6ef
commit 05f36b7b0c
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1 changed files with 44 additions and 7 deletions
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51
googletest/src/gtest-port.cc
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@ -591,12 +591,34 @@ class ThreadLocalRegistryImpl {
// StartWatcherThreadFor to WatcherThreadFunc.
typedef std::pair<DWORD, HANDLE> ThreadIdAndHandle;
class WatcherThreadParams
{
public:
WatcherThreadParams(
DWORD threadId,
HANDLE threadHandle,
std::atomic<bool>* hasWatcherInitialized) :
threadIdAndHandle(threadId, threadHandle),
hasInitialized(hasWatcherInitialized) {
}
ThreadIdAndHandle threadIdAndHandle;
std::atomic<bool>* hasInitialized;
};
static void StartWatcherThreadFor(DWORD thread_id) {
// The returned handle will be kept in thread_map and closed by
// watcher_thread in WatcherThreadFunc.
HANDLE thread =
::OpenThread(SYNCHRONIZE | THREAD_QUERY_INFORMATION, FALSE, thread_id);
GTEST_CHECK_(thread != nullptr);
std::atomic<bool> hasWatcherInitialized = false;
WatcherThreadParams* pThreadParams = new WatcherThreadParams(
thread_id,
thread,
&hasWatcherInitialized);
// We need to pass a valid thread ID pointer into CreateThread for it
// to work correctly under Win98.
DWORD watcher_thread_id;
@ -604,7 +626,7 @@ class ThreadLocalRegistryImpl {
nullptr, // Default security.
0, // Default stack size
&ThreadLocalRegistryImpl::WatcherThreadFunc,
reinterpret_cast<LPVOID>(new ThreadIdAndHandle(thread_id, thread)),
reinterpret_cast<LPVOID>(pThreadParams),
CREATE_SUSPENDED, &watcher_thread_id);
GTEST_CHECK_(watcher_thread != nullptr)
<< "CreateThread failed with error " << ::GetLastError() << ".";
@ -614,17 +636,32 @@ class ThreadLocalRegistryImpl {
::GetThreadPriority(::GetCurrentThread()));
::ResumeThread(watcher_thread);
::CloseHandle(watcher_thread);
// Wait for the watcher thread to start to avoid race conditions.
// One specific race condition that can happen is that we have returned
// from main and have started to tear down, the newly spawned watcher
// thread may access already-freed variables, like global shared_ptrs.
while (hasWatcherInitialized.load() == false) {
std::this_thread::yield();
}
}
// Monitors exit from a given thread and notifies those
// ThreadIdToThreadLocals about thread termination.
static DWORD WINAPI WatcherThreadFunc(LPVOID param) {
const ThreadIdAndHandle* tah =
reinterpret_cast<const ThreadIdAndHandle*>(param);
GTEST_CHECK_(::WaitForSingleObject(tah->second, INFINITE) == WAIT_OBJECT_0);
OnThreadExit(tah->first);
::CloseHandle(tah->second);
delete tah;
WatcherThreadParams* pThreadParams =
reinterpret_cast<WatcherThreadParams*>(param);
const ThreadIdAndHandle tah = pThreadParams->threadIdAndHandle;
// Inform the thread that started us that we have completed initialization
(*pThreadParams->hasInitialized) = true;
delete pThreadParams;
GTEST_CHECK_(::WaitForSingleObject(tah.second, INFINITE) == WAIT_OBJECT_0);
OnThreadExit(tah.first);
::CloseHandle(tah.second);
return 0;
}