https://bugs.kde.org/show_bug.cgi?id=392331
Jens-W. Schicke-Uffmann <drahf...@gmx.de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |drahf...@gmx.de
--- Comment #3 from Jens-W. Schicke-Uffmann <drahf...@gmx.de> ---
I have a reproducer for this warning, which also suggests is spurious (given
the source of the example):
Taking the example from
https://en.cppreference.com/w/cpp/thread/condition_variable:
#include <iostream>
#include <string>
#include <thread>
#include <mutex>
#include <condition_variable>
std::mutex m;
std::condition_variable cv;
std::string data;
bool ready = false;
bool processed = false;
void worker_thread()
{
// Wait until main() sends data
std::unique_lock lk(m);
cv.wait(lk, []{return ready;});
// after the wait, we own the lock.
std::cout << "Worker thread is processing data\n";
data += " after processing";
// Send data back to main()
processed = true;
std::cout << "Worker thread signals data processing completed\n";
// Manual unlocking is done before notifying, to avoid waking up
// the waiting thread only to block again (see notify_one for details)
lk.unlock();
cv.notify_one();
}
int main()
{
std::thread worker(worker_thread);
data = "Example data";
// send data to the worker thread
{
std::lock_guard lk(m);
ready = true;
std::cout << "main() signals data ready for processing\n";
}
cv.notify_one();
// wait for the worker
{
std::unique_lock lk(m);
cv.wait(lk, []{return processed;});
}
std::cout << "Back in main(), data = " << data << '\n';
worker.join();
}
... compiling and running via
% g++-11 -O4 -ggdb test.c++ -lpthread
% valgrind --error-exitcode=1 --exit-on-first-error=yes --tool=helgrind ./a.out
... gives:
[...]
==30543== ---Thread-Announcement------------------------------------------
==30543==
==30543== Thread #1 is the program's root thread
==30543==
==30543== ----------------------------------------------------------------
==30543==
==30543== Thread #1: pthread_cond_{signal,broadcast}: dubious: associated lock
is not held by any thread
==30543== at 0x4847EF6: ??? (in
/usr/libexec/valgrind/vgpreload_helgrind-amd64-linux.so)
==30543== by 0x10A241: main (test2.c++:44)
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