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Fix WebSocket pings being sent early on spurious wakeups

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The heartbeat thread waited on ping_cv_ without a predicate, so a
spurious wakeup ended the wait early and sent a ping before
ping_interval_sec_ had elapsed. With max_missed_pongs enabled, the
early ping also counted toward the pong timeout.

Pass a predicate to wait_for so that the wait only ends when the
interval elapses or the connection is closed.

Reported in #2612.
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yhirose committed 2026-10-03 17:47:30 -04:00
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commit 438319cfcb
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+3 -1
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httplib.h
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@@ -22828,7 +22828,9 @@ inline void WebSocket::start_heartbeat() {
ping_thread_ = std::thread([this]() { ping_thread_ = std::thread([this]() {
std::unique_lock<std::mutex> lock(ping_mutex_); std::unique_lock<std::mutex> lock(ping_mutex_);
while (!closed_) { while (!closed_) {
ping_cv_.wait_for(lock, std::chrono::seconds(ping_interval_sec_)); // The predicate keeps a spurious wakeup from sending a ping early
ping_cv_.wait_for(lock, std::chrono::seconds(ping_interval_sec_),
[this]() { return closed_.load(); });
if (closed_) { break; } if (closed_) { break; }
// If the peer has failed to respond to the previous pings, give up. // If the peer has failed to respond to the previous pings, give up.
// RFC 6455 does not define a pong-timeout mechanism; this is an // RFC 6455 does not define a pong-timeout mechanism; this is an