Dr. Dobb's Journal - November 2008 - (Page 42)

Core Technology WHAT’S NEW IN BOOST THREADS? processing thousands of items, it might make sense to put an interruption point after every 10 or 100 items to enable relatively timely response to the interruption request. Interruption is initially enabled for all threads, but can be disabled by constructing an instance of boost::this_thread::disable_interruption. Interruption is disabled for the lifetime of the disable_interruption object, but only for the thread that created the object. Typically, such an object would be created as a local variable in order to disable interruption around a specific piece of code. For more about thread interruption see my blog entry, entitled “Thread Interruption in the Boost Thread Library” ( w w w . j u s t s o f t w a re s o l u t i o n s. c o. u k / threading/thread-interruption-in-boostthread-library.html). Protecting Shared Data The changes to Boost Threads aren’t just in the thread management interface: The thread synchronization primitives have been changed, too. Probably the most obvious change is that the lock() and unlock() member functions are now public, and the scoped_lock types are just specializations of the new boost::unique_lock template. Because this is a template, it can be used with anything that implements the Lockable concept—which includes instantiations of boost::unique_lock ! Though you wouldn’t generally write boost::unique_lock <boost::unique_lock >, it is helpful in those cases where you wish your code to work with any type of mutex, as users can pass in a lock object instead. For example, it is used as part of the implementation of the new lock() functions for locking more than one mutex together. boost::unique_lock is also movable, so locks can be transferred between objects (and thus between scopes). This makes it much easier to ensure that the mutex is correctly unlocked even when the unlock() is in a different function to the lock(). The flexibility with unique_lock (and the old scoped_lock types) comes at a price—the implementation must hold a flag to indicate whether or not the lock object owns the lock on the mutex, and this must be checked in the destructor. For those cases where you only need strict scoped locking, the boost::lock_guard template provides a smaller, lighter option. It locks the mutex in the constructor and unlocks it in the destructor, cannot be moved and cannot be unlocked without destroying it. A multiple-reader/single-writer mutex has also made a comeback in the form of boost::shared_mutex based on Howard Hinnant’s proposal in N2094 (see www.open-std .org/jtc1/sc22/wg21/docs/papers/2006/ n2094.html). This has a brand new interface, which features the boost::shared_lock template for acquiring shared ownership. It also provides the necessary lock() and unlock() functions, so boost::unique_lock can be used for acquiring exclusive ownership. Dr. Dobb's invites all vendors to participate in the 19th Annual Jolt Product Excellence Awards! Enter your nominations by Friday, October 10, to save 20% off the standard fee. Nominations close November 12, 2008. Winners will be honored at a gala ceremony at SD West 2009. www.JoltAwards.com 42 Dr. Dobb’s Journal l www.ddj.com l November 2008 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2094.html http://www.justsoftwaresolutions.co.uk/threading/thread-interruption-in-boost-thread-library.html http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2094.html http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2094.html http://www.justsoftwaresolutions.co.uk/threading/thread-interruption-in-boost-thread-library.html http://www.justsoftwaresolutions.co.uk/threading/thread-interruption-in-boost-thread-library.html http://www.JoltAwards.com http://www.JoltAwards.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - November 2008

Dr. Dobb's Journal - November 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Developer's Notebook Saving Open Source Conversations iPhone Building Your Own Web Server Green Telnet What's New In Boost Threads? Testing Service Oriented Architectures Test Case Generation, UML, and Eclipse Unit Testing Web Services C3 Programming The Agile Edge Swaine's Flames Effective Concurrency

Dr. Dobb's Journal - November 2008

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