Resolve race on approx_time_ in FastClock.

InitType should hold a lock before storing to approx_time_, which is later read by the background worker. When the worker is actively running (i.e., not blocked on bg_cond_) it holds bg_mutex_. InitType is called during benchmark setup only, so any contention induced for the mutex should not have performance/accuracy consequences.

Resolve race on approx_time_ in FastClock.
2c9b29c9 · Chris Kennelly · efb9c302 · 2c9b29c9
Commit 2c9b29c9 authored May 05, 2014 by Chris Kennelly
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benchmark.cc src/benchmark.cc +1 -0

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--- a/src/benchmark.cc
+++ b/src/benchmark.cc
@@ -577,6 +577,7 @@ class State::FastClock {
  // function starts running - see UseRealTime).
  void InitType(Type type) {
    type_ = type;
+    mutex_lock l(&bg_mutex_);
    std::atomic_store(&approx_time_, NowMicros());
  }