Adobe 38043740 Developing Applications - Page 334

DEVELOPING COLDFUSION 9 APPLICATIONS 329 Developing CFML Applications • End a thread. You typically end a running thread if there is an error, or if it is still processing after a long time. • Have the page or a thread wait until one or more other threads have completed processing before proceeding with its processing, called joining the threads. You typically join threads when one thread requires the results from another thread. For example, if a page uses multiple threads to get several news feeds for display, it joins all the feed threads before it displays the results. Each thread runs the code inside a cfthread tag body and normally exits when the tag body code completes processing. Starting a thread You start a thread by using a cfthread tag with an action attribute value of run. CFML code within the cfthread tag body executes on a separate thread while the page request thread continues processing. Only the page thread can create other threads. A thread that you create with a cfthread tag cannot create a child thread, so you cannot have multiple nested threads. Optionally, when you start the thread, you can specify a priority level of high, normal (the default), or low to specify the relative amount of time that the processor should devote to the thread. Page-level code always runs at normal priority, so you can give your threads more or less processing time than the page. For more information on using thread attributes, see "The Attributes scope and thread attributes" on page 333. Suspending a thread In some cases, one thread must wait until a second thread completes some operations, but should not wait until the second thread completes all processing, so you cannot just join the threads. For example, one thread might do initialization that multiple threads require, and then it might continue with additional processing. The other threads could suspend themselves until initialization is complete. The Sleep function and cfthread tag with a sleepaction attribute provide two equivalent mechanisms for doing such synchronization. They suspend the thread processing for a specified period of time. A code loop could test a condition variable and sleep for a period before retesting the condition. When the condition is true (or a value is reached, or some other test is valid), the program exits the loop and the thread continues processing. The following example shows how one thread could use a sleep function to wait for a second thread to perform some actions. Last updated 1/20/2012