Add TimedWait() API to CondVar.

Summary:
Add TimedWait() API to CondVar, which will be used in the future to
support TimedOut Write API and Rate limiter.

Test Plan: make db_test -j32

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19431

port/port_posix.cc

@@ -9,10 +9,12 @@
 
 #include "port/port_posix.h"
 
-#include <cstdlib>
 #include <stdio.h>
 #include <assert.h>
+#include <errno.h>
+#include <sys/time.h>
 #include <string.h>
+#include <cstdlib>
 #include "util/logging.h"
 
 namespace rocksdb {
@@ -83,6 +85,27 @@ void CondVar::Wait() {
 #endif
 }
 
+bool CondVar::TimedWait(uint64_t abs_time_us) {
+  struct timespec ts;
+  ts.tv_sec = abs_time_us / 1000000;
+  ts.tv_nsec = (abs_time_us % 1000000) * 1000;
+
+#ifndef NDEBUG
+  mu_->locked_ = false;
+#endif
+  int err = pthread_cond_timedwait(&cv_, &mu_->mu_, &ts);
+#ifndef NDEBUG
+  mu_->locked_ = true;
+#endif
+  if (err == ETIMEDOUT) {
+    return true;
+  }
+  if (err != 0) {
+    PthreadCall("timedwait", err);
+  }
+  return false;
+}
+
 void CondVar::Signal() {
   PthreadCall("signal", pthread_cond_signal(&cv_));
 }

port/port_posix.h

@@ -137,6 +137,8 @@ class CondVar {
   explicit CondVar(Mutex* mu);
   ~CondVar();
   void Wait();
+  // Timed condition wait.  Returns true if timeout occurred.
+  bool TimedWait(uint64_t abs_time_us);
   void Signal();
   void SignalAll();
  private: