From 48069f1a3b93bdc04d508f1d63ef5da3665e9a93 Mon Sep 17 00:00:00 2001
From: Nye Liu <nyet@nyet.org>
Date: Fri, 11 Sep 2015 12:24:23 -0700
Subject: [PATCH] Always call wait() at least once even if timeout is 0 to
 prevent deadlocks

---
 src/lib/mt/CondVar.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/lib/mt/CondVar.cpp b/src/lib/mt/CondVar.cpp
index caa12210..75111410 100644
--- a/src/lib/mt/CondVar.cpp
+++ b/src/lib/mt/CondVar.cpp
@@ -66,11 +66,15 @@ CondVarBase::wait(Stopwatch& timer, double timeout) const
 	double remain = timeout-timer.getTime();
 	// Some ARCH wait()s return prematurely, retry until really timed out
 	// In particular, ArchMultithreadPosix::waitCondVar() returns every 100ms
-	while (remain >= 0.0) {
+	do {
+		// Always call wait at least once, even if remain is 0, to give
+		// other thread a chance to grab the mutex to avoid deadlocks on
+        // busy waiting.
+		if (remain<0.0) remain=0.0;
 		if (wait(remain))
 			return true;
 		remain = timeout - timer.getTime();
-	}
+	} while (remain >= 0.0);
 	return false;
 }