Detailed explanation of the start, pause and continue of java threads

A requirement in Android projects: read file contents through threads, and control the start, pause and continue of threads to control the reading of files. Record it here.

Directly in the main thread, the thread (child thread) that reads the file is controlled directly through wait, notify, and notifyAll, and an error is reported: java.lang.IllegalMonitorStateException.

Several issues to note:

1. At any time, the control of the object (monitor) can only be owned by one thread.
2. Whether it is the wait, notify or notifyAll method of the object, it is necessary to ensure that the currently running thread obtains control of the object (monitor).
3. If the above three methods of the object are executed in a thread without control, an error java.lang.IllegalMonitorStateException will be reported.
4. JVM is based on multithreading, and by default, the timing of runtime threads cannot be guaranteed.

Three ways to obtain control of threads:

1. Executes a synchronous instance method of the object.
2. Executes a synchronous static method of the corresponding class of the object.
3. Executes a synchronization block that adds a synchronization lock to the object.

Here we will start, pause, and continue to encapsulate the thread class, and just call the method of this instance directly.

 public class ReadThread implements Runnable{ public Thread t; private String threadName; boolean suspended=false; public ReadThread(String threadName){ this.threadName=threadName; System.out.println("Creating " + threadName ); } public void run() { for(int i = 10; i > 0; i--) { System.out.println("Thread: " + threadName + ", " + i); // Let the thread sleep for a while. try { Thread.sleep(300); synchronized(this) { while(suspended) { wait(); } } } catch (InterruptedException e) { System.out.println("Thread " + threadName + " interrupted."); e.printStackTrace(); } System.out.println("Thread " + threadName + " exiting."); } } /** * Start*/ public void start(){ System.out.println("Starting " + threadName ); if(t==null){ t=new Thread(this, threadName); t.start(); } } /** * Pause*/ void suspend(){ suspended = true; } /** * Continue*/ synchronized void resume(){ suspended = false; notify(); } }

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