libstdc++: Fix testsuite helper functions [PR 97936]

This fixes a race condition in the util/atomic/wait_notify_util.h header
used by several tests, which should make the tests work properly.

libstdc++-v3/ChangeLog:

	PR libstdc++/97936
	* testsuite/29_atomics/atomic/wait_notify/bool.cc: Re-eneable
	test.
	* testsuite/29_atomics/atomic/wait_notify/generic.cc: Likewise.
	* testsuite/29_atomics/atomic/wait_notify/pointers.cc: Likewise.
	* testsuite/29_atomics/atomic_flag/wait_notify/1.cc: Likewise.
	* testsuite/29_atomics/atomic_float/wait_notify.cc: Likewise.
	* testsuite/29_atomics/atomic_integral/wait_notify.cc: Likewise.
	* testsuite/util/atomic/wait_notify_util.h: Fix missed
	notifications by making the new thread wait until the parent
	thread is waiting on the condition variable.

7 files changed, 20 insertions, 10 deletions

diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc
index 29781c6..c14a2391 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc
@@ -2,7 +2,6 @@
 // { dg-do run { target c++2a } }
 // { dg-require-gthreads "" }
 // { dg-additional-options "-pthread" { target pthread } }
-// { dg-skip-if "broken" { ! *-*-*linux } }
 
 // Copyright (C) 2020 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/generic.cc b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/generic.cc
index 629556a..988fe7b 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/generic.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/generic.cc
@@ -2,7 +2,6 @@
 // { dg-do run { target c++2a } }
 // { dg-require-gthreads "" }
 // { dg-additional-options "-pthread" { target pthread } }
-// { dg-skip-if "broken" { ! *-*-*linux } }
 
 // Copyright (C) 2020 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc
index f54961f..8783023 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc
@@ -2,7 +2,6 @@
 // { dg-do run { target c++2a } }
 // { dg-additional-options "-pthread" { target pthread } }
 // { dg-require-gthreads "" }
-// { dg-skip-if "broken" { ! *-*-*linux } }
 
 // Copyright (C) 2020 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
index 763d3e7..991713f 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
@@ -2,7 +2,6 @@
 // { dg-do run { target c++2a } }
 // { dg-require-gthreads "" }
 // { dg-additional-options "-pthread" { target pthread } }
-// { dg-skip-if "broken" { ! *-*-*linux } }
 
 // Copyright (C) 2020 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_float/wait_notify.cc b/libstdc++-v3/testsuite/29_atomics/atomic_float/wait_notify.cc
index 8f9e4a3..134eff3 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_float/wait_notify.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_float/wait_notify.cc
@@ -3,7 +3,6 @@
 // { dg-require-gthreads "" }
 // { dg-additional-options "-pthread" { target pthread } }
 // { dg-add-options libatomic }
-// { dg-skip-if "broken" { ! *-*-*linux } }
 
 // Copyright (C) 2020 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_integral/wait_notify.cc b/libstdc++-v3/testsuite/29_atomics/atomic_integral/wait_notify.cc
index 762583c..c65379c 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_integral/wait_notify.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_integral/wait_notify.cc
@@ -3,7 +3,6 @@
 // { dg-require-gthreads "" }
 // { dg-add-options libatomic }
 // { dg-additional-options "-pthread" { target pthread } }
-// { dg-skip-if "broken" { *-*-* } }
 
 // Copyright (C) 2020 Free Software Foundation, Inc.
 //
diff --git a/libstdc++-v3/testsuite/util/atomic/wait_notify_util.h b/libstdc++-v3/testsuite/util/atomic/wait_notify_util.h
index a319e8b..f5fff4a 100644
--- a/libstdc++-v3/testsuite/util/atomic/wait_notify_util.h
+++ b/libstdc++-v3/testsuite/util/atomic/wait_notify_util.h
@@ -34,16 +34,20 @@ Tp check_wait_notify(Tp val1, Tp val2)
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   std::atomic<Tp> a(val1);
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  a.wait(val1);
 		  if (a.load() != val2)
 		    a = val1;
 		});
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.store(val2);
@@ -59,10 +63,15 @@ Tp check_wait_notify(Tp val1, Tp val2)
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   std::atomic<Tp> a(val1);
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  a.wait(val1);
 		  auto v = a.load();
@@ -70,7 +79,6 @@ Tp check_wait_notify(Tp val1, Tp val2)
 		  if (__builtin_memcmp(&v, &val2, sizeof(Tp)) != 0)
 		    a = val1;
 		});
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.store(val2);
@@ -87,16 +95,20 @@ Tp check_atomic_wait_notify(Tp val1, Tp val2)
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   std::atomic<Tp> a(val1);
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  std::atomic_wait(&a, val1);
 		  if (a.load() != val2)
 		    a = val1;
 		});
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.store(val2);
@@ -112,10 +124,15 @@ Tp check_atomic_wait_notify(Tp val1, Tp val2)
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   std::atomic<Tp> a(val1);
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  std::atomic_wait(&a, val1);
 		  auto v = a.load();
@@ -123,7 +140,6 @@ Tp check_atomic_wait_notify(Tp val1, Tp val2)
 		  if (__builtin_memcmp(&v, &val2, sizeof(Tp)) != 0)
 		    a = val1;
 		});
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.store(val2);