Describes the multi-threaded aspects of the J2ME application environment. Understanding the interactions between systems threads, user-interface and application threads will help in avoiding MIDlet deadlock.
Tutorial Details:
Concurrency - multiple threads executing simultaneously within a single application - is a complex topic. Although Java technology has always included extensive built-in support for multithreading, writing correct concurrent code is seldom as simple as it seems. To give you some welcome help J2SE 5.0 (also called Java 1.5) adds a number of concurrency utilities that are based on work by Doug Lea, author of Concurrent Programming in Java - an excellent reference, well worth reading. These new classes are not available to J2ME applications, unfortunately, so the basic techniques discussed in the article "Using Threads in J2ME Applications" still apply. This tech tip focuses on dealing with system threads, an aspect of MIDP programming that trips up many a beginner.
A system thread is any thread not started and managed by an application. In a MIDP environment, system threads are created by the application management software (AMS) that controls MIDlet execution. Each active application has at least one system thread and zero or more application threads.
Notice that "at least"! An implementation is free to use multiple system threads for different operations or, if necessary, to share system threads among multiple MIDlets - while respecting the MIDlet sandbox and other restrictions. The MIDP specification makes no guarantees as to which threads the AMS uses to perform particular operations.
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