test: cleanup, block threads via semaphore instead of shared_future

No-behavior change.

src/test/threadpool_tests.cpp

@@ -10,6 +10,8 @@
 #include <util/time.h>
 
 #include <boost/test/unit_test.hpp>
+#include <latch>
+#include <semaphore>
 
 // General test values
 int NUM_WORKERS_DEFAULT = 0;
@@ -51,28 +53,18 @@ template <typename F>
     return std::move(*Assert(pool.Submit(std::forward<F>(fn))));
 }
 
-// Block a number of worker threads by submitting tasks that wait on `blocker_future`.
+// Block a number of worker threads by submitting tasks that wait on `release_sem`.
 // Returns the futures of the blocking tasks, ensuring all have started and are waiting.
-std::vector<std::future<void>> BlockWorkers(ThreadPool& threadPool, const std::shared_future<void>& blocker_future, int num_of_threads_to_block)
+std::vector<std::future<void>> BlockWorkers(ThreadPool& threadPool, std::counting_semaphore<>& release_sem, size_t num_of_threads_to_block)
 {
-    // Per-thread ready promises to ensure all workers are actually blocked
+    assert(threadPool.WorkersCount() >= num_of_threads_to_block);
-    std::vector<std::promise<void>> ready_promises(num_of_threads_to_block);
+    std::latch ready{static_cast<std::ptrdiff_t>(num_of_threads_to_block)};
-    std::vector<std::future<void>> ready_futures;
+    std::vector<std::future<void>> blocking_tasks(num_of_threads_to_block);
-    ready_futures.reserve(num_of_threads_to_block);
+    for (auto& f : blocking_tasks) f = Submit(threadPool, [&] {
-    for (auto& p : ready_promises) ready_futures.emplace_back(p.get_future());
+        ready.count_down();
-
+        release_sem.acquire();
-    // Fill all workers with blocking tasks
+    });
-    std::vector<std::future<void>> blocking_tasks;
+    ready.wait();
-    for (int i = 0; i < num_of_threads_to_block; i++) {
-        std::promise<void>& ready = ready_promises[i];
-        blocking_tasks.emplace_back(Submit(threadPool, [blocker_future, &ready]() {
-            ready.set_value();
-            blocker_future.wait();
-        }));
-    }
-
-    // Wait until all threads are actually blocked
-    WAIT_FOR(ready_futures);
     return blocking_tasks;
 }
 
@@ -115,10 +107,8 @@ BOOST_AUTO_TEST_CASE(single_available_worker_executes_all_tasks)
 {
     ThreadPool threadPool(POOL_NAME);
     threadPool.Start(NUM_WORKERS_DEFAULT);
-    // Single blocking future for all threads
+    std::counting_semaphore<> blocker(0);
-    std::promise<void> blocker;
+    const auto blocking_tasks = BlockWorkers(threadPool, blocker, NUM_WORKERS_DEFAULT - 1);
-    std::shared_future<void> blocker_future(blocker.get_future());
-    const auto blocking_tasks = BlockWorkers(threadPool, blocker_future, NUM_WORKERS_DEFAULT - 1);
 
     // Now execute tasks on the single available worker
     // and check that all the tasks are executed.
@@ -132,7 +122,7 @@ BOOST_AUTO_TEST_CASE(single_available_worker_executes_all_tasks)
     WAIT_FOR(futures);
     BOOST_CHECK_EQUAL(counter, num_tasks);
 
-    blocker.set_value();
+    blocker.release(NUM_WORKERS_DEFAULT - 1);
     WAIT_FOR(blocking_tasks);
     threadPool.Stop();
     BOOST_CHECK_EQUAL(threadPool.WorkersCount(), 0);
@@ -195,9 +185,8 @@ BOOST_AUTO_TEST_CASE(process_tasks_manually_when_workers_busy)
     ThreadPool threadPool(POOL_NAME);
     threadPool.Start(NUM_WORKERS_DEFAULT);
 
-    std::promise<void> blocker;
+    std::counting_semaphore<> blocker(0);
-    std::shared_future<void> blocker_future(blocker.get_future());
+    const auto& blocking_tasks = BlockWorkers(threadPool, blocker, NUM_WORKERS_DEFAULT);
-    const auto& blocking_tasks = BlockWorkers(threadPool, blocker_future, NUM_WORKERS_DEFAULT);
 
     // Now submit tasks and check that none of them are executed.
     int num_tasks = 20;
@@ -216,7 +205,7 @@ BOOST_AUTO_TEST_CASE(process_tasks_manually_when_workers_busy)
     }
     BOOST_CHECK_EQUAL(counter.load(), num_tasks);
     BOOST_CHECK_EQUAL(threadPool.WorkQueueSize(), 0);
-    blocker.set_value();
+    blocker.release(NUM_WORKERS_DEFAULT);
     threadPool.Stop();
     WAIT_FOR(blocking_tasks);
 }
@@ -244,9 +233,8 @@ BOOST_AUTO_TEST_CASE(task_submitted_while_busy_completes)
     ThreadPool threadPool(POOL_NAME);
     threadPool.Start(NUM_WORKERS_DEFAULT);
 
-    std::promise<void> blocker;
+    std::counting_semaphore<> blocker(0);
-    std::shared_future<void> blocker_future(blocker.get_future());
+    const auto& blocking_tasks = BlockWorkers(threadPool, blocker, NUM_WORKERS_DEFAULT);
-    const auto& blocking_tasks = BlockWorkers(threadPool, blocker_future, NUM_WORKERS_DEFAULT);
 
     // Submit an extra task that should execute once a worker is free
     std::future<bool> future = Submit(threadPool, []() { return true; });
@@ -257,7 +245,7 @@ BOOST_AUTO_TEST_CASE(task_submitted_while_busy_completes)
     // Wait a short moment before unblocking the threads to mimic a concurrent shutdown
     std::thread thread_unblocker([&blocker]() {
         UninterruptibleSleep(300ms);
-        blocker.set_value();
+        blocker.release(NUM_WORKERS_DEFAULT);
     });
 
     // Stop the pool while the workers are still blocked
@@ -314,13 +302,13 @@ BOOST_AUTO_TEST_CASE(interrupt_blocks_new_submissions)
     // One worker is blocked, another calls Interrupt(), and the remaining one waits for tasks.
     threadPool.Start(/*num_workers=*/3);
     std::atomic<int> counter{0};
-    std::promise<void> blocker;
+    std::counting_semaphore<> blocker(0);
-    const auto blocking_tasks = BlockWorkers(threadPool, blocker.get_future().share(), 1);
+    const auto blocking_tasks = BlockWorkers(threadPool, blocker, 1);
     Submit(threadPool, [&threadPool, &counter]{
         threadPool.Interrupt();
         counter.fetch_add(1, std::memory_order_relaxed);
     }).get();
-    blocker.set_value(); // unblock worker
+    blocker.release(1); // unblock worker
 
     BOOST_CHECK_EQUAL(counter.load(), 1);
     threadPool.Stop();