Efficient Android Threading

Chapter 4. Thread Communication

In multithreaded appplications, tasks can run in parallel and collaborate to produce a result. Hence, threads have to be able to communicate to enable true asynchronous processing. In Android, the importance of thread communication is emphasized in the platform-specific handler/looper mechanism that is the focus in this chapter, together with the traditional Java techniques. The chapter covers:

• Passing data through a one-way data pipe
• Shared memory communication
• Implementing a consumer-producer pattern with BlockingQueue
• Operations on message queues
• Sending tasks back to the UI Thread

Pipes

Pipes are a part of the java.io package. That is, they are general Java functionality and not Android specific. A pipe provides a way for two threads, within the same process, to connect and establish a one-way data channel. A producer thread writes data to the pipe, whereas a consumer thread reads data from the pipe.

Note

The Java pipe is comparable to the Unix and Linux pipe operator (the | shell character) that is used to redirect the output from one command to the input for another command. The pipe operator works across processes in Linux, but Java pipes work across threads in the virtual machine, for example, within a process.

The pipe itself is a circular buffer allocated in memory, available only to the two connected threads. No other threads can access the data. Hence, thread safety—discussed in Thread Safety—is ensured. The pipe is also one-directional, ...