[gcc r11-5447] libstdc++: Fix some more deadlocks in tests [PR 97936]

[gcc r11-5447] libstdc++: Fix some more deadlocks in tests [PR 97936]

[Jonathan Wakely]

https://gcc.gnu.org/g:10522ed1089277e2aa6cd708205aa5c730179cf0

commit r11-5447-g10522ed1089277e2aa6cd708205aa5c730179cf0
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 26 12:55:47 2020 +0000

    libstdc++: Fix some more deadlocks in tests [PR 97936]
    
    The missed notifications fixed in r11-5383 also happen in some other
    tests which have similar code.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/97936
            * testsuite/29_atomics/atomic/wait_notify/bool.cc: Fix missed
            notifications by making the new thread wait until the parent
            thread is waiting on the condition variable.
            * testsuite/29_atomics/atomic/wait_notify/pointers.cc: Likewise.
            * testsuite/29_atomics/atomic_flag/wait_notify/1.cc: Likewise.
            * testsuite/29_atomics/atomic_ref/wait_notify.cc: Likewise.

Diff:
---
 libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc     | 6 +++++-
 libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc | 6 +++++-
 libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc   | 6 +++++-
 libstdc++-v3/testsuite/29_atomics/atomic_ref/wait_notify.cc      | 6 +++++-
 4 files changed, 20 insertions(+), 4 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 c14a2391d68..1fc01491173 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/bool.cc
@@ -36,11 +36,16 @@ main ()
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   std::atomic<bool> a(false);
   std::atomic<bool> b(false);
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  a.wait(false);
 		  if (a.load())
@@ -48,7 +53,6 @@ main ()
 		      b.store(true);
 		    }
 		});
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.store(true);
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 87830236e0e..3b699e9133b 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/pointers.cc
@@ -36,6 +36,7 @@ main ()
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   long aa;
   long bb;
@@ -43,12 +44,15 @@ main ()
   std::atomic<long*> a(nullptr);
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  a.wait(nullptr);
 		  if (a.load() == &aa)
 		    a.store(&bb);
 		});
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.store(&aa);
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 991713fbcde..5d5e06dde31 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
@@ -36,18 +36,22 @@ main()
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   std::atomic_flag a;
   std::atomic_flag b;
   std::thread t([&]
 		{
+		  {
+		    // This ensures we block until cv.wait(l) starts.
+		    std::lock_guard<std::mutex> ll(m);
+		  }
 		  cv.notify_one();
 		  a.wait(false);
 		  b.test_and_set();
 		  b.notify_one();
 		});
 
-  std::unique_lock<std::mutex> l(m);
   cv.wait(l);
   std::this_thread::sleep_for(100ms);
   a.test_and_set();
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_ref/wait_notify.cc b/libstdc++-v3/testsuite/29_atomics/atomic_ref/wait_notify.cc
index b38fc206d46..bc5a7d0d8bf 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_ref/wait_notify.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_ref/wait_notify.cc
@@ -37,17 +37,21 @@ Tp check_wait_notify(Tp val1, Tp val2)
 
   std::mutex m;
   std::condition_variable cv;
+  std::unique_lock<std::mutex> l(m);
 
   Tp aa = val1;
   std::atomic_ref<Tp> a(aa);
   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);