Fix thread pool tests

runtime/vm/thread_pool_test.cc

Index: runtime/vm/thread_pool_test.cc
diff --git a/runtime/vm/thread_pool_test.cc b/runtime/vm/thread_pool_test.cc
index 48d2125b332d83a7e02ebddf7765a2f57fd76fdf..a555503eae905c57ef2514497de7cd3e7c01bcae 100644
--- a/runtime/vm/thread_pool_test.cc
+++ b/runtime/vm/thread_pool_test.cc
@@ -23,7 +23,17 @@ class TestTask : public ThreadPool::Task {
       : sync_(sync), done_(done) {
   }
 
+  // Before running the task, *done_ should be true. This lets the caller
+  // ASSERT things knowing that the thread is still around. To unblock the
+  // thread, the caller should take the lock, set *done_ to false, and Notify()
+  // the monitor.
   virtual void Run() {
+    {
+      MonitorLocker ml(sync_);
+      while (*done_) {
+        ml.Wait();
+      }
+    }
     MonitorLocker ml(sync_);
     *done_ = true;
     ml.Notify();
@@ -38,10 +48,12 @@ class TestTask : public ThreadPool::Task {
 UNIT_TEST_CASE(ThreadPool_RunOne) {
   ThreadPool thread_pool;
   Monitor sync;
-  bool done = false;
+  bool done = true;
   thread_pool.Run(new TestTask(&sync, &done));
   {
     MonitorLocker ml(&sync);
+    done = false;
+    ml.Notify();
     while (!done) {
       ml.Wait();
     }
@@ -61,11 +73,13 @@ UNIT_TEST_CASE(ThreadPool_RunMany) {
   bool done[kTaskCount];
 
   for (int i = 0; i < kTaskCount; i++) {
-    done[i] = false;
+    done[i] = true;
     thread_pool.Run(new TestTask(&sync[i], &done[i]));
   }
   for (int i = 0; i < kTaskCount; i++) {
     MonitorLocker ml(&sync[i]);
+    done[i] = false;
+    ml.Notify();
     while (!done[i]) {
       ml.Wait();
     }
@@ -157,12 +171,14 @@ UNIT_TEST_CASE(ThreadPool_WorkerTimeout) {
 
   // Run a worker.
   Monitor sync;
-  bool done = false;
+  bool done = true;
   thread_pool.Run(new TestTask(&sync, &done));
   EXPECT_EQ(1U, thread_pool.workers_started());
   EXPECT_EQ(0U, thread_pool.workers_stopped());
   {
     MonitorLocker ml(&sync);
+    done = false;
+    ml.Notify();
     while (!done) {
       ml.Wait();
     }