DBTest.GetThreadStatus: Wait for test results for longer

Summary:
The current 10 millisecond waiting for test results may not be sufficient in some test environments. Increase it to 60 seconds and check the results for every 1 milliseond.

Already reviewed: https://reviews.facebook.net/D65457
Closes https://github.com/facebook/rocksdb/pull/1437

Differential Revision: D4099443

Pulled By: siying

fbshipit-source-id: cf1f205

db/db_test.cc

@@ -3646,15 +3646,25 @@ TEST_F(DBTest, GetThreadStatus) {
       env_->SetBackgroundThreads(kHighPriCounts[test], Env::HIGH);
       env_->SetBackgroundThreads(kLowPriCounts[test], Env::LOW);
       // Wait to ensure the all threads has been registered
-      env_->SleepForMicroseconds(100000);
+      unsigned int thread_type_counts[ThreadStatus::NUM_THREAD_TYPES];
+      // Try up to 60 seconds.
+      for (int num_try = 0; num_try < 60000; num_try++) {
+        env_->SleepForMicroseconds(1000);
+        thread_list.clear();
         s = env_->GetThreadList(&thread_list);
         ASSERT_OK(s);
-      unsigned int thread_type_counts[ThreadStatus::NUM_THREAD_TYPES];
         memset(thread_type_counts, 0, sizeof(thread_type_counts));
         for (auto thread : thread_list) {
           ASSERT_LT(thread.thread_type, ThreadStatus::NUM_THREAD_TYPES);
           thread_type_counts[thread.thread_type]++;
         }
+        if (thread_type_counts[ThreadStatus::HIGH_PRIORITY] ==
+                kHighPriCounts[test] &&
+            thread_type_counts[ThreadStatus::LOW_PRIORITY] ==
+                kLowPriCounts[test]) {
+          break;
+        }
+      }
       // Verify the total number of threades
       ASSERT_EQ(thread_type_counts[ThreadStatus::HIGH_PRIORITY] +
                     thread_type_counts[ThreadStatus::LOW_PRIORITY],