Thread start and priority

start()  and  run()  The difference between

start() Source code ：

public synchronized void start() {
 if (threadStatus != 0)
 throw new IllegalThreadStateException();
 group.add(this);
 boolean started = false;
 try {
 start0();
 started = true;
 } finally {
 try {
 if (!started) {
 group.threadStartFailed(this);
 }
 } catch (Throwable ignore) {
 //  Don't handle any exceptions , If  start0  Throw an exception , Then it will be passed to the call stack
 }
 }
}


if (threadStatus != 0) throw new IllegalThreadStateException();

State verification , It's not equal to  NEW  An exception will be thrown

group.add(this);

Notification thread group , This thread is about to start

catch (Throwable ignore) { }

Do not do any exception handling , If an exception is thrown , Will be passed to the called method

run() Source code ：

public class Thread implements Runnable {
 
 ......
 
 private Runnable target;
 @Override
 public void run() {
 if (target != null) {
 target.run();
 }
 }
}


run() Method where is overridden Runnable Interface run Method . and start()  The method belongs to  Thread  Own approach , And used synchronized, Guaranteed thread safety .

start()  Method is the method of starting thread , Let the thread from  NEW  The state changes to  RUNNABLE  state , and  run()  Method is just a common method , It will not affect the state of the thread .

Thread priority

What is the priority of threads ？ Thread priority is used by thread scheduling to determine when each thread is allowed to run first . Theoretically, threads with high priority are more likely to get more than threads with low priority CPU Time . It's not that the priority thread must execute first .

stay java Threads Thread Class source code , The properties of thread priority are 3 individual ：

public final static int MIN_PRIORITY = 1;

public final static int NORM_PRIORITY = 5;

public final static int MAX_PRIORITY = 10


MIN_PRIORITY Indicates the minimum priority that a thread can have

NORM_PRIORITY Indicates the default priority of the thread

MAX_PRIORITY Indicates the maximum priority that a thread can have

Method of modifying thread priority ：setPriority(), Source code ：

public final void setPriority(int newPriority) {
 ThreadGroup g;
 checkAccess();
 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
 throw new IllegalArgumentException();
 }
 if((g = getThreadGroup()) != null) {
 if (newPriority > g.getMaxPriority()) {
 newPriority = g.getMaxPriority();
 }
 setPriority0(priority = newPriority);
 }
}


 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) { }

Verify the rationality of priority , If it is beyond the reasonable range , It will be thrown out. IllegalArgumentException abnormal

 if (newPriority > g.getMaxPriority()) { newPriority = g.getMaxPriority();}

If the priority exceeds the highest priority of the thread group , Set the priority to the highest priority of the thread group , Therefore, the priority of threads may not be the same as the set value , Also please the priority of the thread group .