libstdc++: Simplify std::try_lock and std::lock further

The std::try_lock and std::lock algorithms can use iteration instead of
recursion when all lockables have the same type and can be held by an
array of unique_lock<L> objects.

By making this change to __detail::__try_lock_impl it also benefits
__detail::__lock_impl, which uses it. For std::lock we can just put the
iterative version directly in std::lock, to avoid making any call to
__detail::__lock_impl.

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

Co-authored-by: Matthias Kretz <m.kretz@gsi.de>

libstdc++-v3/ChangeLog:

	* include/std/mutex (lock): Replace recursion with iteration
	when lockables all have the same type.
	(__detail::__try_lock_impl): Likewise. Pass lockables as
	parameters, instead of a tuple. Always lock the first one, and
	recurse for the rest.
	(__detail::__lock_impl): Adjust call to __try_lock_impl.
	(__detail::__try_to_lock): Remove.
	* testsuite/30_threads/lock/3.cc: Check that mutexes are locked.
	* testsuite/30_threads/lock/4.cc: Also test non-heterogeneous
	arguments.
	* testsuite/30_threads/unique_lock/cons/60497.cc: Also check
	std::try_lock.
	* testsuite/30_threads/try_lock/5.cc: New test.

4 files changed, 174 insertions, 1 deletions

diff --git a/libstdc++-v3/testsuite/30_threads/lock/3.cc b/libstdc++-v3/testsuite/30_threads/lock/3.cc
index 5213607..5fa1187 100644
--- a/libstdc++-v3/testsuite/30_threads/lock/3.cc
+++ b/libstdc++-v3/testsuite/30_threads/lock/3.cc
@@ -37,7 +37,7 @@ struct user_lock
     is_locked = true;
   }
 
-  bool try_lock() 
+  bool try_lock()
   { return is_locked ? false : (is_locked = true); }
 
   void unlock()
@@ -62,6 +62,8 @@ int main()
 	{
 	  //heterogeneous types
 	  std::lock(m1, m2, m3);
+	  VERIFY( !m1.try_lock() );
+	  VERIFY( !m3.try_lock() );
 	  m1.unlock();
 	  m2.unlock();
 	  m3.unlock();
diff --git a/libstdc++-v3/testsuite/30_threads/lock/4.cc b/libstdc++-v3/testsuite/30_threads/lock/4.cc
index 7ba15cb..130c1f6 100644
--- a/libstdc++-v3/testsuite/30_threads/lock/4.cc
+++ b/libstdc++-v3/testsuite/30_threads/lock/4.cc
@@ -73,6 +73,7 @@ int unreliable_lock::lock_on = -1;
 void test01()
 {
   unreliable_lock l1, l2, l3;
+  std::mutex m1, m2, m3;
 
   try
     {
@@ -87,6 +88,60 @@ void test01()
     {
       VERIFY( false );
     }
+
+  // Repeat with non-heterogeneous arguments
+
+  try
+    {
+      unreliable_lock::count = 0;
+      std::lock(l1, l2, l3, m1);
+      VERIFY( unreliable_lock::count == 3 );
+      l1.unlock();
+      l2.unlock();
+      l3.unlock();
+      VERIFY( !m1.try_lock() ); // already locked
+      m1.unlock();
+    }
+  catch (...)
+    {
+      VERIFY( false );
+    }
+
+  try
+    {
+      unreliable_lock::count = 0;
+      std::lock(m1, l1, l2, l3);
+      VERIFY( unreliable_lock::count == 3 );
+      VERIFY( !m1.try_lock() ); // already locked
+      m1.unlock();
+      l1.unlock();
+      l2.unlock();
+      l3.unlock();
+    }
+  catch (...)
+    {
+      VERIFY( false );
+    }
+
+  try
+    {
+      unreliable_lock::count = 0;
+      std::lock(l1, m1, l2, m2, l3, m3);
+      VERIFY( unreliable_lock::count == 3 );
+      l1.unlock();
+      l2.unlock();
+      l3.unlock();
+      VERIFY( !m1.try_lock() ); // already locked
+      VERIFY( !m2.try_lock() ); // already locked
+      VERIFY( !m3.try_lock() ); // already locked
+      m1.unlock();
+      m2.unlock();
+      m3.unlock();
+    }
+  catch (...)
+    {
+      VERIFY( false );
+    }
 }
 
 void test02()
@@ -111,6 +166,31 @@ void test02()
     {
       VERIFY( false );
     }
+
+  // Repeat with non-heterogeneous arguments
+
+  try
+    {
+      unreliable_lock::lock_on = 1;
+      while (unreliable_lock::lock_on < 3)
+      {
+        unreliable_lock::count = 0;
+        unreliable_lock l1, l2, l3;
+	std::mutex m1;
+        std::lock(l1, l2, l3, m1);
+        VERIFY( unreliable_lock::count > 3 );
+        l1.unlock();
+        l2.unlock();
+        l3.unlock();
+	VERIFY( !m1.try_lock() ); // already locked
+        m1.unlock();
+        ++unreliable_lock::lock_on;
+      }
+    }
+  catch (...)
+    {
+      VERIFY( false );
+    }
 }
 
 void test03()
@@ -133,6 +213,50 @@ void test03()
     VERIFY( test );
     ++unreliable_lock::throw_on;
   }
+
+  // Repeat with non-heterogeneous arguments
+
+  unreliable_lock::throw_on = 0;
+  while (unreliable_lock::throw_on < 3)
+  {
+    unreliable_lock::count = 0;
+    unreliable_lock l1, l2, l3;
+    std::mutex m1;
+    bool test = false;
+    try
+      {
+        std::lock(l1, l2, l3, m1);
+      }
+    catch (...)
+      {
+        test = true;
+      }
+    VERIFY( test );
+    VERIFY( m1.try_lock() ); // m1 was not left locked by failed std::lock
+    m1.unlock();
+    ++unreliable_lock::throw_on;
+  }
+
+  unreliable_lock::throw_on = 0;
+  while (unreliable_lock::throw_on < 3)
+  {
+    unreliable_lock::count = 0;
+    unreliable_lock l1, l2, l3;
+    std::mutex m1;
+    bool test = false;
+    try
+      {
+        std::lock(m1, l1, l2, l3);
+      }
+    catch (...)
+      {
+        test = true;
+      }
+    VERIFY( test );
+    VERIFY( m1.try_lock() ); // m1 was not left locked by failed std::lock
+    m1.unlock();
+    ++unreliable_lock::throw_on;
+  }
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/30_threads/try_lock/5.cc b/libstdc++-v3/testsuite/30_threads/try_lock/5.cc
new file mode 100644
index 0000000..a5574ff
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/try_lock/5.cc
@@ -0,0 +1,41 @@
+// { dg-do run { target c++11 } }
+
+#include <mutex>
+#include <testsuite_hooks.h>
+
+struct Lockable
+{
+  static int tries;
+
+  void lock() { }
+  void unlock() { }
+  bool try_lock() { return ++tries != 2; }
+};
+
+int Lockable::tries = 0;
+
+void test01()
+{
+  Lockable l1, l2, l3;
+  std::mutex m1, m2;
+
+  VERIFY( std::try_lock(l1, l2, l3) == 1 );
+  VERIFY( Lockable::tries == 2 );
+
+  Lockable::tries = 0;
+  VERIFY( std::try_lock(m1, l1, l2, l3) == 2 );
+  VERIFY( Lockable::tries == 2 );
+
+  Lockable::tries = 0;
+  VERIFY( std::try_lock(l1, l2, l3, m1) == 1 );
+  VERIFY( Lockable::tries == 2 );
+
+  Lockable::tries = 0;
+  VERIFY( std::try_lock(m1, l1, l2, l3, m2) == 2 );
+  VERIFY( Lockable::tries == 2 );
+}
+
+int main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/30_threads/unique_lock/cons/60497.cc b/libstdc++-v3/testsuite/30_threads/unique_lock/cons/60497.cc
index 8603e56..08698ce 100644
--- a/libstdc++-v3/testsuite/30_threads/unique_lock/cons/60497.cc
+++ b/libstdc++-v3/testsuite/30_threads/unique_lock/cons/60497.cc
@@ -46,3 +46,9 @@ void test02()
   test_type l1, l2, l3;
   std::lock(l1, l2, l3);
 }
+
+void test03()
+{
+  test_type l1, l2, l3;
+  std::try_lock(l1, l2, l3);
+}