Author: allison Date: Wed Dec 27 22:28:19 2006 New Revision: 16280 Modified: trunk/docs/pdds/clip/pdd22_io.pod
Log: [pdd]: Adding notes on the async I/O concurrency model. Modified: trunk/docs/pdds/clip/pdd22_io.pod ============================================================================== --- trunk/docs/pdds/clip/pdd22_io.pod (original) +++ trunk/docs/pdds/clip/pdd22_io.pod Wed Dec 27 22:28:19 2006 @@ -62,21 +62,31 @@ they don't need opcodes. They can access the functionality via methods on ParrotIO objects. -Asynchronous operations don't use Parrot threads, they use a -light-weight concurrency model for asynchronous operations. The -asynchronous I/O implementation will use the composition model to +The asynchronous I/O implementation will use the composition model to allow some platforms to take advantage of their built-in asynchronous -operations instead of using Parrot's concurrency implementation. +operations, layered behind Parrot's asynchronous I/O interface. -[Type up review of options for the I/O concurrency model.] +Asynchronous operations use a lightweight concurrency model. At the user +level, Parrot follows the callback function model of asynchronous I/O. +At the interpreter level, each asynchronous operation registers a task +with the interpreter's concurrency scheduler. The registered task could +represent a simple Parrot asynchronous I/O operation, a platform-native +asynchronous I/O call, or even synchronous code in a full Parrot thread +(rare but possibly useful for prototyping new features, or for mock +objects in testing). Communication between the calling code and the asynchronous operation -thread will be handled by a shared status object. The operation thread -will update the status object whenever the status changes, and the -calling code can check the status object at any time. The status object -contains a reference to the returned result of an asynchronous I/O call. - +task is handled by a shared status object. The operation task updates +the status object whenever the status changes, and the calling code can +check the status object at any time. The status object contains a +reference to the returned result of an asynchronous I/O call. + +The lightweight tasks typically used by the asynchronous I/O system +capture no state other than the arguments passed to the I/O call, and +share no variables with the calling code other than the status object. +[See http://en.wikipedia.org/wiki/Asynchronous_I/O, for a relatively +comprehensive list of asynchronous I/O implementation options.] =head2 I/O PMC API
