thread（线）.doc

thread（线） Multithreading ======================= Thread: a process in a process The difference between threads and processes: Each process requires the operating system to allocate separate memory address space for it. All threads in each process work in the same memory space, which share the same memory space and system resources. There are two ways to build threads: 1. extend the java.lang.Thread class 2. implement the java.lang.Runnable interface The java.lang.Thread class represents the thread class. The two main methods are: 1. run () represents the code executed by the thread at run time 2. start () used to start threads A thread can only be started once. The java.lang.IllegalThreadStateException exception is thrown at the second boot Transition between threads 1. new status. The thread object created with the new statement is in a new state. At the same time, it allocates memory address space only in the heap, just like any other Java object 2. ready state. When a thread is created, the start method is called to start the thread, when the thread enters the ready state. The thread in readiness is in the running pool, waiting for access to CUP 3. run. At this point, the thread takes up CPU and executes the program 4. blocked state. When the thread is blocked, the Java virtual machine does not assign CUP resources to it until the thread is ready again There are three kinds of blocking states: 1. is located in the object waiting pool occlusion: when the thread is running, if the wait method of the A object is executed, the Java virtual machine puts the thread into the waiting pool of the A object 2. block located in the object lock: when the thread is running, trying to get the synchronization lock of the A object, if the A objects synchronization lock has been occupied by another thread, JVM will put the thread into the synchronous lock of the A object. 3. other congestion: when a sleep method is called, or a join method of another thread is called, or a I/O req