Test thread priority inheritance on add() on non-dynamic CPUThreadPoolExecutor

Summary:
If `CPUThreadPoolExecutor` is configured without dynamic thread creation, it is expected that no new threads are created on `add()`. This is important because `add()` may come from threads with different priority, and that would be inherited by the newly created threads.

Using static size protects from that behavior. This is widely depended on, so we should have a test for it.

Reviewed By: uvdn7

Differential Revision: D79378022

fbshipit-source-id: 3ccbd305a001b0cdd09e7142a6ee0ddb1a44c73a

Author: ot

third-party/folly/src/folly/executors/test/ThreadPoolExecutorTest.cpp

@@ -14,33 +14,31 @@
  * limitations under the License.
  */
 
-#include <folly/CPortability.h>
-#include <folly/DefaultKeepAliveExecutor.h>
-#include <folly/executors/CPUThreadPoolExecutor.h>
-#include <folly/executors/ThreadPoolExecutor.h>
-#include <folly/lang/Keep.h>
-#include <folly/synchronization/Latch.h>
-
 #include <atomic>
 #include <memory>
 #include <thread>
 
 #include <boost/thread.hpp>
-
+#include <folly/CPortability.h>
+#include <folly/DefaultKeepAliveExecutor.h>
 #include <folly/Exception.h>
 #include <folly/container/F14Map.h>
+#include <folly/executors/CPUThreadPoolExecutor.h>
 #include <folly/executors/EDFThreadPoolExecutor.h>
 #include <folly/executors/FutureExecutor.h>
 #include <folly/executors/IOThreadPoolExecutor.h>
+#include <folly/executors/ThreadPoolExecutor.h>
 #include <folly/executors/VirtualExecutor.h>
 #include <folly/executors/task_queue/LifoSemMPMCQueue.h>
 #include <folly/executors/task_queue/UnboundedBlockingQueue.h>
 #include <folly/executors/thread_factory/InitThreadFactory.h>
 #include <folly/executors/thread_factory/PriorityThreadFactory.h>
+#include <folly/lang/Keep.h>
 #include <folly/portability/GMock.h>
 #include <folly/portability/GTest.h>
 #include <folly/portability/PThread.h>
 #include <folly/portability/SysResource.h>
+#include <folly/synchronization/Latch.h>
 #include <folly/synchronization/detail/Spin.h>
 #include <folly/system/ThreadId.h>
 
@@ -626,6 +624,29 @@ TEST(ThreadPoolExecutorTest, BlockingQueue) {
   EXPECT_EQ(5, c);
 }
 
+TEST(ThreadPoolExecutorTest, NoThreadPriorityInheritance) {
+  constexpr size_t kNumThreads = 16;
+  const auto initialPriority = getpriority(PRIO_PROCESS, 0);
+
+  // If minThreads == maxThreads, no threads should be created on add(), and
+  // thus they should not inherit the parent thread's priority. Instead, all
+  // threads should inherit the priority at the time of construction.
+  CPUThreadPoolExecutor exe{std::make_pair(kNumThreads, kNumThreads)};
+
+  // Nice the current thread.
+  setpriority(PRIO_PROCESS, 0, 19);
+
+  Latch ready{kNumThreads + 1};
+  for (size_t i = 0; i < kNumThreads; ++i) {
+    exe.add([&] {
+      EXPECT_EQ(getpriority(PRIO_PROCESS, 0), initialPriority);
+      ready.arrive_and_wait();
+    });
+  }
+  ready.arrive_and_wait();
+  exe.join();
+}
+
 TEST(PriorityThreadFactoryTest, ThreadPriority) {
   errno = 0;
   auto currentPriority = getpriority(PRIO_PROCESS, 0);