1 files changed, 44 insertions, 2 deletions
diff --git a/indra/llcommon/llthread.h b/indra/llcommon/llthread.h
index 0fb89c5613..376df398d7 100755
--- a/indra/llcommon/llthread.h
+++ b/indra/llcommon/llthread.h
@@ -4,7 +4,7 @@
  *
  * $LicenseInfo:firstyear=2004&license=viewerlgpl$
  * Second Life Viewer Source Code
- * Copyright (C) 2010, Linden Research, Inc.
+ * Copyright (C) 2010-2013, Linden Research, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -156,7 +156,8 @@ public:
 	virtual ~LLMutex();
 	
 	void lock();		// blocks
-	void unlock();
+	bool trylock();		// non-blocking, returns true if lock held.
+	void unlock();		// undefined behavior when called on mutex not being held
 	bool isLocked(); 	// non-blocking, but does do a lock/unlock so not free
 	bool isSelfLocked(); //return true if locked in a same thread
 	U32 lockingThread() const; //get ID of locking thread
@@ -174,6 +175,8 @@ protected:
 #endif
 };
 
+//============================================================================
+
 // Actually a condition/mutex pair (since each condition needs to be associated with a mutex).
 class LL_COMMON_API LLCondition : public LLMutex
 {
@@ -189,6 +192,8 @@ protected:
 	apr_thread_cond_t *mAPRCondp;
 };
 
+//============================================================================
+
 class LLMutexLock
 {
 public:
@@ -210,6 +215,43 @@ private:
 
 //============================================================================
 
+// Scoped locking class similar in function to LLMutexLock but uses
+// the trylock() method to conditionally acquire lock without
+// blocking.  Caller resolves the resulting condition by calling
+// the isLocked() method and either punts or continues as indicated.
+//
+// Mostly of interest to callers needing to avoid stalls who can
+// guarantee another attempt at a later time.
+
+class LLMutexTrylock
+{
+public:
+	LLMutexTrylock(LLMutex* mutex)
+		: mMutex(mutex),
+		  mLocked(false)
+	{
+		if (mMutex)
+			mLocked = mMutex->trylock();
+	}
+
+	~LLMutexTrylock()
+	{
+		if (mMutex && mLocked)
+			mMutex->unlock();
+	}
+
+	bool isLocked() const
+	{
+		return mLocked;
+	}
+	
+private:
+	LLMutex*	mMutex;
+	bool		mLocked;
+};
+
+//============================================================================
+
 void LLThread::lockData()
 {
 	mDataLock->lock();