cpp: Fix a race/deadlock in ThreadManager

When removing a task from the pending queue, we were only notifying a
blocked thread waiting to enqueue a task if the number of pending tasks
was exactly one less than the limit.  However, if two tasks are finished
at about the same time, this can result in two spots being freed up with
only one notify.  With this change, we always notify on task completion,
eliminating the race/deadlock.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@920680 13f79535-47bb-0310-9956-ffa450edef68

diff --git a/lib/cpp/src/concurrency/ThreadManager.cpp b/lib/cpp/src/concurrency/ThreadManager.cpp
index d0bb41f..aee57f3 100644 (file)
--- a/lib/cpp/src/concurrency/ThreadManager.cpp
+++ b/lib/cpp/src/concurrency/ThreadManager.cpp
@@ -295,7 +295,7 @@ class ThreadManager::Worker: public Runnable {
             /* If we have a pending task max and we just dropped below it, wakeup any
                thread that might be blocked on add. */
             if (manager_->pendingTaskCountMax_ != 0 &&
-                manager_->tasks_.size() == manager_->pendingTaskCountMax_ - 1) {
+                manager_->tasks_.size() <= manager_->pendingTaskCountMax_ - 1) {
               manager_->maxMonitor_.notify();
             }
           }