Dr. Dobb's Journal - July 2008 - (Page 45)

sleep() or yield() function available on your system: T Consume(int wait_time = 1/*milliseconds*/) { T tmp; while (!Consume(tmp)) { Sleep(wait_time/*milliseconds*/); } return tmp; } Figure 3: Ping-Pong test results. The DoSleep() can be implemented using nanosleep() (POSIX) or Sleep() (Windows), or even better, using boost::thread::sleep(), which abstracts away system-dependent nomenclature. Call this approach SLEEP. Instead of simple polling, you can use more advanced techniques to signal the Consumer thread that a new element is available. I illustrate this in Listing One using a boost::condition variable. I used the timed_wait() instead of the simpler wait() to solve a possible deadlock when Produce() is called between line A and line B in Listing One. Then wait() will miss the notify_one() call and have to wait for the next produced element to wake up. If this element never comes (no more produced elements or if the Produce() call actually waits for Consume() to return), there’s a deadlock. Call this approach TIME_WAIT. The lock is still wait-free as long as there are elements in the queue. In this case, the Consumer() thread does no waiting and reads data as fast as possible (even with the Producer() that is inserting new elements). Only when the queue is exhausted does locking occur. The Ping-Pong Test To compare the three approaches (NAIVE_POLLING, SLEEP, and TIME_WAIT), I implemented a test called “Ping-Pong” that is similar to the game of table tennis (the source code is available online). In Figure 2, there are two identical queues between the threads T1 and T2. You first load one of the queues with a number of “balls,” then ask each thread to read from one I/O Controls x x x x x High-Speed for Real-Time applications Built-In custom Property Editors Automatic and Custom Sizing. No Restrictive Bitmaps Look and Feel of Real Hardware Includes : Switches, Gauges, Sliders, Led’s, Led Bar, Led Spiral, Integer/Binary/Hexadecimal Displays, Tanks, Valves, Motors, LCD Matrix, Spectrum Display, Percent and Pie Graph, Odometers, Analog Clock, Image Display, Rotation Display, and Mode Combo Box. Plot Control x x x x x x x x High-Speed for Real-Time applications Unlimited Number of Channels & Axes Full Customizable External Toolbar Legends, Tables, Limits, Labels, Annotations, Cursors Gradient Backgrounds Log Files and Data Export and Import Save images to BMP, PNG, JPEG, TIF, GIF and EMF Many built in channel types : Tracy, Trace-XY, Bar, Bubble, Fill, Bi-Fill, Digital, Differential and Sweep Interval (EKG) Std Pack .Net x 28 Controls x Basic I/O Controls ActiveX & VCL Also Available Pro Pack .Net x 55 Controls x Basic & Advanced I/O Controls Single Developer : $1099 Additional Developer : $379 ActiveX & VCL Also Available Plot Pack .Net x Plotting : Scientific, Engineering, Strip-Chart, Digital, EKG, and more ActiveX & VCL Also Available Ultra Pack .Net x 56 Controls x Basic & Advanced I/O Controls plus Plotting Single Developer : $1699 Additional Developer : $579 ActiveX & VCL Also Available Single Developer : $559 Additional Developer : $189 Single Developer : $859 Additional Developer : $289 www.iocomp.com 888-599-2929 +1-407-226-3456 7081 Grand National Drive Suite 112, Orlando, FL 32819 July 2008 l www.ddj.com l Dr. Dobb’s Journal 45 http://www.iocomp.com http://www.ddj.com

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

Dr. Dobb's Journal - July 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Developer’s Notebook Engineers Without Borders Conversations Patricia Tries Event-Based Architectures Graphs Versus Objects Lock-Free Queues Dr. Dobb’s Architecture & Design World Java and the Nokia N10 Internet Tablet Effective Concurrency The Agile Edge Swaine’s Flames

Dr. Dobb's Journal - July 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.