[llvm/Support] Make llvm::sys::RWMutex Lockable

This patch extends the `llvm::sys::RWMutex` class to fullfill the
`Lockable` requirement to include attempted locking, by implementing a
`bool try_lock` member function.

As the name suggests, this method will try to acquire to lock in a
non-blocking fashion and release it immediately. If it managed to
acquire the lock, returns `true`, otherwise returns `false`.

Signed-off-by: Med Ismail Bennani <[email protected]>

Author: medismailben

llvm/include/llvm/Support/RWMutex.h

@@ -75,6 +75,10 @@ class RWMutexImpl {
   /// Unconditionally release the lock in write mode.
   bool unlock();
 
+  /// Attempts to acquire the lock. Returns immediately.
+  /// @returns true on successful lock acquisition, false otherwise.
+  bool try_lock();
+
   //@}
   /// @name Platform Dependent Data
   /// @{
@@ -148,6 +152,8 @@ template <bool mt_only> class SmartRWMutex {
     --writers;
     return true;
   }
+
+  bool try_lock() { return impl.try_lock(); }
 };
 
 typedef SmartRWMutex<false> RWMutex;

llvm/lib/Support/RWMutex.cpp

@@ -28,6 +28,7 @@ bool RWMutexImpl::lock_shared() { return true; }
 bool RWMutexImpl::unlock_shared() { return true; }
 bool RWMutexImpl::lock() { return true; }
 bool RWMutexImpl::unlock() { return true; }
+bool RWMutexImpl::try_lock() { return true; }
 
 #else
 
@@ -107,6 +108,14 @@ RWMutexImpl::unlock()
   return errorcode == 0;
 }
 
+bool RWMutexImpl::try_lock() {
+  pthread_rwlock_t *rwlock = static_cast<pthread_rwlock_t *>(data_);
+  assert(rwlock != nullptr);
+
+  int errorcode = pthread_rwlock_tryrdlock(rwlock);
+  return errorcode == 0;
+}
+
 #else
 
 RWMutexImpl::RWMutexImpl() : data_(new MutexImpl(false)) { }
@@ -131,6 +140,10 @@ bool RWMutexImpl::unlock() {
   return static_cast<MutexImpl *>(data_)->release();
 }
 
+bool RWMutexImpl::try_lock() {
+  return static_cast<MutexImpl *>(data_)->tryacquire();
+}
+
 #endif
 #endif
 #endif