Commit 8e68ffb8 authored by Changli Gao's avatar Changli Gao Committed by Islam AbdelRahman
Browse files

Fix deadlock when calling getMergedHistogram

When calling StatisticsImpl::HistogramInfo::getMergedHistogram(), if
there is a dying thread, which is calling
ThreadLocalPtr::StaticMeta::OnThreadExit() to merge its thread values to
HistogramInfo, deadlock will occur. Because the former try to hold
merge_lock then ThreadMeta::mutex_, but the later try to hold
ThreadMeta::mutex_ then merge_lock. In short, the locking order isn't
the same.

This patch addressed this issue by releasing merge_lock before folding
thread values.

Differential Revision: D4211942

Pulled By: ajkr

fbshipit-source-id: ef89bcb
parent 41526f44
......@@ -51,9 +51,11 @@ uint64_t StatisticsImpl::getTickerCount(uint32_t tickerType) const {
StatisticsImpl::HistogramInfo::getMergedHistogram() const {
MutexLock lock(&merge_lock);
std::unique_ptr<HistogramImpl> res_hist(new HistogramImpl());
MutexLock lock(&merge_lock);
[](void* curr_ptr, void* res) {
auto tmp_res_hist = static_cast<HistogramImpl*>(res);
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