libstdc++: Add nodiscard attribute to mutex try_lock functions

libstdc++-v3/ChangeLog:

	* include/bits/std_mutex.h (mutex): Add nodiscard attribute to
	try_lock member function.
	* include/bits/unique_lock.h (unique_lock): Likewise for
	try_lock, try_lock_until, try_lock_for member functions, and
	owns_lock and mutex member functions.
	* include/std/mutex (recursive_mutex): Likewise for try_lock
	member function.
	(timed_mutex, recursive_timed_mutex, try_lock): Likewise for
	try_lock, try_lock_until, try_lock_for member functions.
	(try_lock): Likewise for non-member function.
	* include/std/shared_mutex (shared_mutex): Likewise for try_lock
	and try_lock_shared member functions.
	(shared_timed_mutex): Likewise for try_lock, try_lock_for,
	try_lock_shared, try_lock_shared_for, try_lock_until, and
	try_lock_shared_until member functions.
	(shared_lock): Likewise for try_lock, try_lock, try_lock_for,
	try_lock_until, owns_lock, and mutex member functions.
	* testsuite/30_threads/recursive_timed_mutex/try_lock_until/clock_neg.cc:
	Cast discarded value expression to void.
	* testsuite/30_threads/shared_lock/locking/3.cc: Likewise.
	* testsuite/30_threads/shared_lock/locking/4.cc: Likewise.
	* testsuite/30_threads/shared_lock/locking/clock_neg.cc:
	Likewise.
	* testsuite/30_threads/shared_timed_mutex/try_lock_until/clock_neg.cc:
	Likewise.
	* testsuite/30_threads/timed_mutex/try_lock_until/clock_neg.cc:
	Likewise.
	* testsuite/30_threads/try_lock/4.cc: Likewise.
	* testsuite/30_threads/unique_lock/cons/60497.cc: Likewise.
	* testsuite/30_threads/unique_lock/locking/3.cc: Likewise.
	* testsuite/30_threads/unique_lock/locking/clock_neg.cc:
	Likewise.

1 files changed, 19 insertions, 3 deletions

diff --git a/libstdc++-v3/include/std/shared_mutex b/libstdc++-v3/include/std/shared_mutex
index cf74b32..7b70697 100644
--- a/libstdc++-v3/include/std/shared_mutex
+++ b/libstdc++-v3/include/std/shared_mutex
@@ -420,13 +420,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Exclusive ownership
 
     void lock() { _M_impl.lock(); }
-    bool try_lock() { return _M_impl.try_lock(); }
+    [[nodiscard]] bool try_lock() { return _M_impl.try_lock(); }
     void unlock() { _M_impl.unlock(); }
 
     // Shared ownership
 
     void lock_shared() { _M_impl.lock_shared(); }
-    bool try_lock_shared() { return _M_impl.try_lock_shared(); }
+    [[nodiscard]] bool try_lock_shared() { return _M_impl.try_lock_shared(); }
     void unlock_shared() { _M_impl.unlock_shared(); }
 
 #if _GLIBCXX_USE_PTHREAD_RWLOCK_T
@@ -473,10 +473,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Exclusive ownership
 
     void lock() { _Base::lock(); }
-    bool try_lock() { return _Base::try_lock(); }
+    _GLIBCXX_NODISCARD bool try_lock() { return _Base::try_lock(); }
     void unlock() { _Base::unlock(); }
 
     template<typename _Rep, typename _Period>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
       {
@@ -489,10 +490,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Shared ownership
 
     void lock_shared() { _Base::lock_shared(); }
+    _GLIBCXX_NODISCARD
     bool try_lock_shared() { return _Base::try_lock_shared(); }
     void unlock_shared() { _Base::unlock_shared(); }
 
     template<typename _Rep, typename _Period>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_shared_for(const chrono::duration<_Rep, _Period>& __rtime)
       {
@@ -507,6 +510,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Exclusive ownership
 
     template<typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_until(const chrono::time_point<chrono::system_clock,
 		     _Duration>& __atime)
@@ -532,6 +536,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #ifdef _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK
     template<typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_until(const chrono::time_point<chrono::steady_clock,
 		   _Duration>& __atime)
@@ -558,6 +563,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
     template<typename _Clock, typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
       {
@@ -580,6 +586,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Shared ownership
 
     template<typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_shared_until(const chrono::time_point<chrono::system_clock,
 			    _Duration>& __atime)
@@ -619,6 +626,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #ifdef _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK
     template<typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_shared_until(const chrono::time_point<chrono::steady_clock,
 			    _Duration>& __atime)
@@ -645,6 +653,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
     template<typename _Clock, typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_shared_until(const chrono::time_point<_Clock,
 						     _Duration>& __atime)
@@ -670,6 +679,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Exclusive ownership
 
     template<typename _Clock, typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_until(const chrono::time_point<_Clock, _Duration>& __abs_time)
       {
@@ -694,6 +704,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // Shared ownership
 
     template <typename _Clock, typename _Duration>
+      _GLIBCXX_NODISCARD
       bool
       try_lock_shared_until(const chrono::time_point<_Clock,
 						     _Duration>& __abs_time)
@@ -776,6 +787,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	_M_owns = true;
       }
 
+      _GLIBCXX_NODISCARD
       bool
       try_lock()
       {
@@ -784,6 +796,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
       template<typename _Rep, typename _Period>
+	_GLIBCXX_NODISCARD
 	bool
 	try_lock_for(const chrono::duration<_Rep, _Period>& __rel_time)
 	{
@@ -792,6 +805,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
 
       template<typename _Clock, typename _Duration>
+	_GLIBCXX_NODISCARD
 	bool
 	try_lock_until(const chrono::time_point<_Clock, _Duration>& __abs_time)
 	{
@@ -826,10 +840,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // Getters
 
+      _GLIBCXX_NODISCARD
       bool owns_lock() const noexcept { return _M_owns; }
 
       explicit operator bool() const noexcept { return _M_owns; }
 
+      _GLIBCXX_NODISCARD
       mutex_type* mutex() const noexcept { return _M_pm; }
 
     private: