haiku/docs/user/support/Autolock.dox

/*
 * Copyright 2007 Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Niels Sascha Reedijk, niels.reedijk@gmail.com
 *
 * Corresponds to:
 *		headers/os/support/Autolock.h	rev 19972
 */


/*!
	\file Autolock.h
	\ingroup support
	\ingroup libroot
	\brief Implements a handy locking utility.
*/


/*!
	\class BAutolock
	\ingroup support
	\ingroup libroot
	\brief Convenient utility to make parts of your code thread-safe easily.

	The autolocker uses a BLooper or a BLocker in order to protect a part
	of your code. This class is usually used in combination with a BLocker
	that protects a certain part of your code and data that are being
	accessed by multiple threads. While BAutolock does not add any features
	to locking, it provides a mechanism to easily lock and protect a part of your
	code. 

	Normally, when you need to protect data, you would have to make sure that
	all your locks are paired with unlocks. Below is a simple example, but you
	can imagine that there are more complex situations where you might spend a
	lot of time debugging a hang because you didn't pair all the Lock()s with an
	Unlock(). See the example:

\code
status_t
Receiver::HandleCall(Call *call)
{
	... work on call data ...
	 fDataLocker->Lock()
	 ... perform changes ...
	 if (!success)
	{
	  fDataLocker->Unlock();
	  return B_ERROR;
	}
	  
	fDataLocker->Unlock()
	return B_OK;
}
\endcode
	With the BAutolock this example can be rewritten as follows:

\code
status_t
Receiver::HandleCall(Call *call)
{
	... work on call data ...
	
	BAutolock autolock(fDataLocker);
	
	... perform changes ...
	
	if (!success)
	  return B_ERROR;
	
	return B_OK;
}
\endcode

	Since the object is created on stack, it is destroyed as soon as we leave
	the function. Because the destruction of the object causes it to unlock
	the BLocker or BLooper, you don't have to manually make sure that every
	exit from the function is properly unlocked.
*/


/*!
	\fn BAutolock::BAutolock(BLooper *looper)
	\brief Create an object and lock the BLooper
*/


/*!
	\fn BAutolock::BAutolock(BLocker *locker)
	\brief Create an object and lock the BLocker
*/


/*!
	\fn BAutolock::BAutolock(BLocker &locker)
	\brief Create an object and lock the BLocker
*/


/*!
	\fn BAutolock::~BAutolock()
	\brief Destroy the object and unlock the associated BLocker or BLooper
*/


/*!
	\fn bool BAutolock::IsLocked(void)
	\brief Verify whether the  associated BLocker or BLooper are actually
		locked.

	Basically you may assume that when the object is created, you are
	almost always sure the actual locking succeeds. It might fail if the
	BLocker or BLooper are destroyed though. The semaphore will be
	released and the Lock() call will fail.

	If you expect this to happen, you can use this method to help you
	protect yourself from any harm.
	\retval true The lock was acquired.
	\retval false Failed to acquire the lock.
*/