libstdc++: Fix for deadlock in std::counting_semaphore [PR100806]

Message ID 20210616195218.1451153-1-rodgert@appliantology.com
State New
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Series
  • libstdc++: Fix for deadlock in std::counting_semaphore [PR100806]
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Commit Message

Thomas Rodgers June 16, 2021, 7:52 p.m.
Same as previous version except removing the copyright notice from the
test.

libstdc++-v3/ChangeLog:
	libstdc++/PR100806
	* include/bits/semaphore_base.h (__atomic_semaphore::_M_release():
	Force _M_release() to wake all waiting threads.
	* testsuite/30_threads/semaphore/100806.cc: New test.
---
 libstdc++-v3/include/bits/semaphore_base.h    |  4 +-
 .../testsuite/30_threads/semaphore/100806.cc  | 60 +++++++++++++++++++
 2 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

-- 
2.26.2

Comments

Tamar Christina via Gcc-patches June 17, 2021, 4:45 p.m. | #1
On Wed, 16 Jun 2021 at 20:53, Thomas Rodgers <rodgert@appliantology.com> wrote:
>

> Same as previous version except removing the copyright notice from the

> test.

>

> libstdc++-v3/ChangeLog:

>         libstdc++/PR100806

>         * include/bits/semaphore_base.h (__atomic_semaphore::_M_release():

>         Force _M_release() to wake all waiting threads.

>         * testsuite/30_threads/semaphore/100806.cc: New test.


OK for trunk and 11, thanks.


> ---

>  libstdc++-v3/include/bits/semaphore_base.h    |  4 +-

>  .../testsuite/30_threads/semaphore/100806.cc  | 60 +++++++++++++++++++

>  2 files changed, 63 insertions(+), 1 deletion(-)

>  create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

>

> diff --git a/libstdc++-v3/include/bits/semaphore_base.h b/libstdc++-v3/include/bits/semaphore_base.h

> index 9a55978068f..c4565d7e560 100644

> --- a/libstdc++-v3/include/bits/semaphore_base.h

> +++ b/libstdc++-v3/include/bits/semaphore_base.h

> @@ -256,7 +256,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

>        if (__update > 1)

>         __atomic_notify_address_bare(&_M_counter, true);

>        else

> -       __atomic_notify_address_bare(&_M_counter, false);

> +       __atomic_notify_address_bare(&_M_counter, true);

> +// FIXME - Figure out why this does not wake a waiting thread

> +//     __atomic_notify_address_bare(&_M_counter, false);

>      }

>

>    private:

> diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc b/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

> new file mode 100644

> index 00000000000..938c2793be1

> --- /dev/null

> +++ b/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

> @@ -0,0 +1,60 @@

> +// { dg-options "-std=gnu++2a -pthread" }

> +// { dg-do run { target c++2a } }

> +// { dg-require-effective-target pthread }

> +// { dg-require-gthreads "" }

> +// { dg-add-options libatomic }

> +

> +#include <array>

> +#include <iostream>

> +#include <sstream>

> +

> +#include <thread>

> +#include <semaphore>

> +#include <mutex>

> +#include <chrono>

> +#include <vector>

> +

> +std::counting_semaphore<4> semaphore{6};

> +

> +std::mutex mtx;

> +std::vector<std::string> results;

> +

> +void thread_main(size_t x)

> +{

> +  semaphore.acquire();

> +  std::this_thread::sleep_for(std::chrono::milliseconds(100));

> +  semaphore.release();

> +  {

> +    std::ostringstream stm;

> +    stm << "Thread " << x << " finished.";

> +    std::lock_guard g{ mtx };

> +    results.push_back(stm.str());

> +  }

> +}

> +

> +int main()

> +{

> +

> +    constexpr auto nthreads = 10;

> +

> +    std::vector<std::thread> threads(nthreads);

> +

> +

> +    size_t counter{0};

> +    for(auto& t : threads)

> +    {

> +        t = std::thread(thread_main, counter++);

> +    }

> +

> +    for(auto& t : threads)

> +      {

> +        t.join();

> +        {

> +          std::lock_guard g{ mtx };

> +          for (auto&& r : results)

> +            std::cout << r << '\n';

> +          std::cout.flush();

> +          results.clear();

> +        }

> +      }

> +}

> --

> 2.26.2

>
Tamar Christina via Gcc-patches June 22, 2021, 6:09 p.m. | #2
Tested x86_64-pc-linux-gnu.
Committed to master, backported to releases/gcc-11.

On Thu, Jun 17, 2021 at 9:46 AM Jonathan Wakely <jwakely.gcc@gmail.com>
wrote:

> On Wed, 16 Jun 2021 at 20:53, Thomas Rodgers <rodgert@appliantology.com>

> wrote:

> >

> > Same as previous version except removing the copyright notice from the

> > test.

> >

> > libstdc++-v3/ChangeLog:

> >         libstdc++/PR100806

> >         * include/bits/semaphore_base.h

> (__atomic_semaphore::_M_release():

> >         Force _M_release() to wake all waiting threads.

> >         * testsuite/30_threads/semaphore/100806.cc: New test.

>

> OK for trunk and 11, thanks.

>

>

> > ---

> >  libstdc++-v3/include/bits/semaphore_base.h    |  4 +-

> >  .../testsuite/30_threads/semaphore/100806.cc  | 60 +++++++++++++++++++

> >  2 files changed, 63 insertions(+), 1 deletion(-)

> >  create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

> >

> > diff --git a/libstdc++-v3/include/bits/semaphore_base.h

> b/libstdc++-v3/include/bits/semaphore_base.h

> > index 9a55978068f..c4565d7e560 100644

> > --- a/libstdc++-v3/include/bits/semaphore_base.h

> > +++ b/libstdc++-v3/include/bits/semaphore_base.h

> > @@ -256,7 +256,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

> >        if (__update > 1)

> >         __atomic_notify_address_bare(&_M_counter, true);

> >        else

> > -       __atomic_notify_address_bare(&_M_counter, false);

> > +       __atomic_notify_address_bare(&_M_counter, true);

> > +// FIXME - Figure out why this does not wake a waiting thread

> > +//     __atomic_notify_address_bare(&_M_counter, false);

> >      }

> >

> >    private:

> > diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

> b/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

> > new file mode 100644

> > index 00000000000..938c2793be1

> > --- /dev/null

> > +++ b/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc

> > @@ -0,0 +1,60 @@

> > +// { dg-options "-std=gnu++2a -pthread" }

> > +// { dg-do run { target c++2a } }

> > +// { dg-require-effective-target pthread }

> > +// { dg-require-gthreads "" }

> > +// { dg-add-options libatomic }

> > +

> > +#include <array>

> > +#include <iostream>

> > +#include <sstream>

> > +

> > +#include <thread>

> > +#include <semaphore>

> > +#include <mutex>

> > +#include <chrono>

> > +#include <vector>

> > +

> > +std::counting_semaphore<4> semaphore{6};

> > +

> > +std::mutex mtx;

> > +std::vector<std::string> results;

> > +

> > +void thread_main(size_t x)

> > +{

> > +  semaphore.acquire();

> > +  std::this_thread::sleep_for(std::chrono::milliseconds(100));

> > +  semaphore.release();

> > +  {

> > +    std::ostringstream stm;

> > +    stm << "Thread " << x << " finished.";

> > +    std::lock_guard g{ mtx };

> > +    results.push_back(stm.str());

> > +  }

> > +}

> > +

> > +int main()

> > +{

> > +

> > +    constexpr auto nthreads = 10;

> > +

> > +    std::vector<std::thread> threads(nthreads);

> > +

> > +

> > +    size_t counter{0};

> > +    for(auto& t : threads)

> > +    {

> > +        t = std::thread(thread_main, counter++);

> > +    }

> > +

> > +    for(auto& t : threads)

> > +      {

> > +        t.join();

> > +        {

> > +          std::lock_guard g{ mtx };

> > +          for (auto&& r : results)

> > +            std::cout << r << '\n';

> > +          std::cout.flush();

> > +          results.clear();

> > +        }

> > +      }

> > +}

> > --

> > 2.26.2

> >

>

>

Patch

diff --git a/libstdc++-v3/include/bits/semaphore_base.h b/libstdc++-v3/include/bits/semaphore_base.h
index 9a55978068f..c4565d7e560 100644
--- a/libstdc++-v3/include/bits/semaphore_base.h
+++ b/libstdc++-v3/include/bits/semaphore_base.h
@@ -256,7 +256,9 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       if (__update > 1)
 	__atomic_notify_address_bare(&_M_counter, true);
       else
-	__atomic_notify_address_bare(&_M_counter, false);
+	__atomic_notify_address_bare(&_M_counter, true);
+// FIXME - Figure out why this does not wake a waiting thread
+//	__atomic_notify_address_bare(&_M_counter, false);
     }
 
   private:
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc b/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc
new file mode 100644
index 00000000000..938c2793be1
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/100806.cc
@@ -0,0 +1,60 @@ 
+// { dg-options "-std=gnu++2a -pthread" }
+// { dg-do run { target c++2a } }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+// { dg-add-options libatomic }
+
+#include <array>
+#include <iostream>
+#include <sstream>
+
+#include <thread>
+#include <semaphore>
+#include <mutex>
+#include <chrono>
+#include <vector>
+
+std::counting_semaphore<4> semaphore{6};
+
+std::mutex mtx;
+std::vector<std::string> results; 
+
+void thread_main(size_t x)
+{
+  semaphore.acquire();
+  std::this_thread::sleep_for(std::chrono::milliseconds(100));
+  semaphore.release();
+  {
+    std::ostringstream stm;
+    stm << "Thread " << x << " finished.";
+    std::lock_guard g{ mtx };
+    results.push_back(stm.str());
+  }
+}
+
+int main()
+{
+    
+    constexpr auto nthreads = 10;
+
+    std::vector<std::thread> threads(nthreads);
+
+
+    size_t counter{0};
+    for(auto& t : threads)
+    {
+        t = std::thread(thread_main, counter++);
+    }
+
+    for(auto& t : threads)
+      {
+        t.join();
+        {
+          std::lock_guard g{ mtx };
+          for (auto&& r : results)
+            std::cout << r << '\n';
+          std::cout.flush();
+          results.clear();
+        }
+      }
+}