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Fix shutdown deadlock in PicoQuicTransport and qclient signal handling #767

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Fix shutdown deadlock in PicoQuicTransport and qclient signal handling #767

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3162f3b
Fix shutdown deadlock
bifurcation Jan 27, 2026
cc3a1a0
Use atomic<bool>
bifurcation Jan 27, 2026
5d1d4f6
Make load explicit
bifurcation Jan 27, 2026
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10 changes: 5 additions & 5 deletions cmd/examples/client.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1172,9 +1172,6 @@ main(int argc, char* argv[])
// Install a signal handlers to catch operating system signals
installSignalHandlers();

// Lock the mutex so that main can then wait on it
std::unique_lock lock(moq_example::main_mutex);

bool enable_pub{ false };
bool enable_sub{ false };
bool enable_fetch{ false };
Expand All @@ -1190,14 +1187,17 @@ main(int argc, char* argv[])
exit(-1);
}

while (not stop_threads) {
while (not stop_threads && not moq_example::terminate.load()) {
if (client->GetStatus() == MyClient::Status::kReady) {
Comment on lines 1189 to 1191
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@chatgpt-codex-connector chatgpt-codex-connector bot Jan 27, 2026

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P2 Badge Synchronize terminate flag read during connect loop

In the connect loop, moq_example::terminate is now read without holding main_mutex, but the signal handler writes it under that mutex (signal_handler.h). If a SIGINT arrives while this loop is running, the handler can write concurrently with this unsynchronized read, which is a data race/UB and can cause missed termination or undefined behavior. Consider making terminate an std::atomic<bool> or taking the same mutex when reading it here.

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SPDLOG_INFO("Connected to server");
break;
}
std::this_thread::sleep_for(std::chrono::milliseconds(200));
}

// Lock the mutex for cv.wait
std::unique_lock lock(moq_example::main_mutex);

std::thread pub_thread;
std::thread sub_thread;
std::thread fetch_thread;
Expand Down Expand Up @@ -1258,7 +1258,7 @@ main(int argc, char* argv[])
}

// Wait until told to terminate
moq_example::cv.wait(lock, [&]() { return moq_example::terminate; });
moq_example::cv.wait(lock, [&]() { return moq_example::terminate.load(); });

stop_threads = true;
SPDLOG_INFO("Stopping threads...");
Expand Down
2 changes: 1 addition & 1 deletion cmd/examples/server.cpp
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Expand Up @@ -1065,7 +1065,7 @@ main(int argc, char* argv[])
}

// Wait until told to terminate
moq_example::cv.wait(lock, [&]() { return moq_example::terminate; });
moq_example::cv.wait(lock, [&]() { return moq_example::terminate.load(); });

// Unlock the mutex
lock.unlock();
Expand Down
3 changes: 2 additions & 1 deletion cmd/examples/signal_handler.h
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Expand Up @@ -3,14 +3,15 @@

#pragma once

#include <atomic>
#include <condition_variable>
#include <csignal>
#include <iostream>
#include <mutex>

namespace moq_example {
std::mutex main_mutex; // Main's mutex
bool terminate{ false }; // Termination flag
std::atomic<bool> terminate{ false }; // Termination flag
std::condition_variable cv; // Main thread waits on this
const char* termination_reason{ nullptr }; // Termination reason
};
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3 changes: 3 additions & 0 deletions src/transport_picoquic.cpp
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Expand Up @@ -2628,6 +2628,9 @@ PicoQuicTransport::Shutdown()

if (quic_network_thread_ctx_ != NULL) {
SPDLOG_LOGGER_INFO(logger, "Closing transport picoquic thread");

// Signal thread to exit BEFORE waiting
quic_network_thread_ctx_->thread_should_close = 1;
picoquic_wake_up_network_thread(quic_network_thread_ctx_);

while (quic_network_thread_ctx_->thread_is_ready) {
Expand Down