[libcxx-commits] [libcxx] [libc++][test] atomit wait test take 2 (PR #169206)
via libcxx-commits
libcxx-commits at lists.llvm.org
Sat Dec 6 23:51:21 PST 2025
https://github.com/huixie90 updated https://github.com/llvm/llvm-project/pull/169206
>From bf78bf3d839bbcb4a6555e32bbc150ef4371cbf4 Mon Sep 17 00:00:00 2001
From: Hui Xie <hui.xie1990 at gmail.com>
Date: Sat, 22 Nov 2025 17:37:22 +0000
Subject: [PATCH 1/5] [libc++] test for atomic::wait
---
.../lost_wakeup.pass.cpp | 58 +++++++++++++++++++
1 file changed, 58 insertions(+)
create mode 100644 libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
new file mode 100644
index 0000000000000..5a0d587815828
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: no-threads
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// This is a stress test for std::atomic::wait for lost wake ups.
+
+// <atomic>
+
+#include <atomic>
+#include <functional>
+#include <thread>
+#include <vector>
+
+#include "make_test_thread.h"
+
+constexpr int num_waiters = 8;
+constexpr int num_iterations = 10'000;
+
+int main(int, char**) {
+ for (int run = 0; run < 20; ++run) {
+ std::atomic<int> waiter_ready(0);
+ std::atomic<int> state(0);
+
+ auto wait = [&]() {
+ for (int i = 0; i < num_iterations; ++i) {
+ auto old_state = state.load(std::memory_order_acquire);
+ waiter_ready.fetch_add(1, std::memory_order_acq_rel);
+ state.wait(old_state, std::memory_order_acquire);
+ }
+ };
+
+ auto notify = [&] {
+ for (int i = 0; i < num_iterations; ++i) {
+ while (waiter_ready.load(std::memory_order_acquire) < num_waiters) {
+ std::this_thread::yield();
+ }
+ waiter_ready.store(0, std::memory_order_release);
+ state.fetch_add(1, std::memory_order_acq_rel);
+ state.notify_all();
+ }
+ };
+
+ std::vector<std::jthread> threads;
+ for (int i = 0; i < num_waiters; ++i)
+ threads.push_back(support::make_test_jthread(wait));
+
+ threads.push_back(support::make_test_jthread(notify));
+ }
+
+ return 0;
+}
>From 020f47f84a5711208379e83626a5f31af0576d8f Mon Sep 17 00:00:00 2001
From: Hui Xie <hui.xie1990 at gmail.com>
Date: Sun, 23 Nov 2025 09:36:57 +0000
Subject: [PATCH 2/5] seq_cst
---
.../lost_wakeup.pass.cpp | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
index 5a0d587815828..fc96ea1a8f201 100644
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
@@ -30,19 +30,19 @@ int main(int, char**) {
auto wait = [&]() {
for (int i = 0; i < num_iterations; ++i) {
- auto old_state = state.load(std::memory_order_acquire);
- waiter_ready.fetch_add(1, std::memory_order_acq_rel);
- state.wait(old_state, std::memory_order_acquire);
+ auto old_state = state.load();
+ waiter_ready.fetch_add(1);
+ state.wait(old_state);
}
};
auto notify = [&] {
for (int i = 0; i < num_iterations; ++i) {
- while (waiter_ready.load(std::memory_order_acquire) < num_waiters) {
+ while (waiter_ready.load() < num_waiters) {
std::this_thread::yield();
}
- waiter_ready.store(0, std::memory_order_release);
- state.fetch_add(1, std::memory_order_acq_rel);
+ waiter_ready.store(0);
+ state.fetch_add(1);
state.notify_all();
}
};
>From 0beef0957d43a5fa93276a5a2910ddc2724c08c9 Mon Sep 17 00:00:00 2001
From: Hui Xie <hui.xie1990 at gmail.com>
Date: Sat, 6 Dec 2025 15:13:59 +0000
Subject: [PATCH 3/5] remove yield and add debug
---
.../atomics.types.operations.wait/lost_wakeup.pass.cpp | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
index fc96ea1a8f201..293d2f94fb93a 100644
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
@@ -17,6 +17,7 @@
#include <functional>
#include <thread>
#include <vector>
+#include <iostream>
#include "make_test_thread.h"
@@ -25,6 +26,7 @@ constexpr int num_iterations = 10'000;
int main(int, char**) {
for (int run = 0; run < 20; ++run) {
+ std::cerr << "run " << run << std::endl;
std::atomic<int> waiter_ready(0);
std::atomic<int> state(0);
@@ -38,8 +40,11 @@ int main(int, char**) {
auto notify = [&] {
for (int i = 0; i < num_iterations; ++i) {
+ if (i % 1000 == 0)
+ std::cerr << "run " << run << " notify iteration " << i << std::endl;
+
while (waiter_ready.load() < num_waiters) {
- std::this_thread::yield();
+ // std::this_thread::yield();
}
waiter_ready.store(0);
state.fetch_add(1);
>From eb741e996ff88c401c729a8275ae1f87b85e68a6 Mon Sep 17 00:00:00 2001
From: Hui Xie <hui.xie1990 at gmail.com>
Date: Sat, 6 Dec 2025 21:13:06 +0000
Subject: [PATCH 4/5] test
---
.../atomics.types.operations.wait/lost_wakeup.pass.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
index 293d2f94fb93a..a16271835f626 100644
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
@@ -44,7 +44,7 @@ int main(int, char**) {
std::cerr << "run " << run << " notify iteration " << i << std::endl;
while (waiter_ready.load() < num_waiters) {
- // std::this_thread::yield();
+ std::this_thread::yield();
}
waiter_ready.store(0);
state.fetch_add(1);
>From 380e26389dbed4575d672c2153073ea0b42f0cef Mon Sep 17 00:00:00 2001
From: Hui Xie <hui.xie1990 at gmail.com>
Date: Sun, 7 Dec 2025 07:51:09 +0000
Subject: [PATCH 5/5] more debug
---
.../atomics.types.operations.wait/lost_wakeup.pass.cpp | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
index a16271835f626..7d5f1929566de 100644
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp
@@ -14,10 +14,12 @@
// <atomic>
#include <atomic>
+#include <chrono>
#include <functional>
#include <thread>
#include <vector>
#include <iostream>
+#include <iomanip>
#include "make_test_thread.h"
@@ -25,6 +27,7 @@ constexpr int num_waiters = 8;
constexpr int num_iterations = 10'000;
int main(int, char**) {
+ auto start = std::chrono::high_resolution_clock::now();
for (int run = 0; run < 20; ++run) {
std::cerr << "run " << run << std::endl;
std::atomic<int> waiter_ready(0);
@@ -41,7 +44,9 @@ int main(int, char**) {
auto notify = [&] {
for (int i = 0; i < num_iterations; ++i) {
if (i % 1000 == 0)
- std::cerr << "run " << run << " notify iteration " << i << std::endl;
+ std::cerr << std::fixed << std::setprecision(2) << std::left
+ << std::chrono::duration<double>(std::chrono::high_resolution_clock::now() - start) << " run "
+ << run << " notify iteration " << i << std::endl;
while (waiter_ready.load() < num_waiters) {
std::this_thread::yield();
@@ -59,5 +64,5 @@ int main(int, char**) {
threads.push_back(support::make_test_jthread(notify));
}
- return 0;
+ return 1;
}
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