max*_*max 8 java linux multithreading pthreads jstack
我打算在我的Java代码中使用线程优先级.应用程序应在我的Linux系统上运行:
>uname -a
Linux <host> 3.0.0-15-generic #26-Ubuntu SMP <date> x86_64 x86_64 x86_64 GNU/Linux
>java -version
java version "1.6.0_23"
OpenJDK Runtime Environment (IcedTea6 1.11pre) (6b23~pre11-0ubuntu1.11.10.1)
OpenJDK 64-Bit Server VM (build 20.0-b11, mixed mode)
在Web上阅读完之后,我现在使用以下命令启动我的测试应用程序:
sudo java -XX:+UseThreadPriorities -XX:ThreadPriorityPolicy=1 -jar ThreadPriorityTest.jar
测试应用程序包含以下两个类:
package ch.mypackage;
public class CountingRunnable implements Runnable{
private long count=0;
private boolean goOn=true;
public long getCount() {
return count;
}
public void stop(){
goOn=false;
}
public void run() {
for(long iteration=0;goOn&&iteration<Long.MAX_VALUE;++iteration){
++count;
}
}
}
package ch.mypackage;
public class PriorizedCountingThreads {
private static final int NUM_MILLIS_TO_COUNT_FOR = 1*60*1000;
private static CountingRunnable[] runnables;
private static Thread[] threads;
/**
* @param args
*/
public static void main(String[] args) {
Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
System.out.println("MIN_PRIORITY: "+Thread.MIN_PRIORITY);
System.out.println("MAX_PRIORITY: "+Thread.MAX_PRIORITY);
int numPriorityLevels=(Thread.MAX_PRIORITY-Thread.MIN_PRIORITY)+1;
init(numPriorityLevels);
startThreads();
try {
Thread.sleep(NUM_MILLIS_TO_COUNT_FOR);
} catch (InterruptedException e) {
e.printStackTrace();
}
stopRunnables();
printCounts();
}
private static void printCounts() {
for(int i=0;i<runnables.length;++i){
System.out.println(threads[i].getName()+" has priority: "+threads[i].getPriority()+" and count:"+runnables[i].getCount());
}
}
private static void stopRunnables() {
for(int i=0;i<runnables.length;++i){
runnables[i].stop();
}
}
private static void startThreads() {
for(int i=0;i<threads.length;++i){
threads[i].start();
}
}
private static void init(int numPriorityLevels) {
runnables=new CountingRunnable[numPriorityLevels];
threads=new Thread[runnables.length];
for(int i=0;i<runnables.length;++i){
int priority=i+1;
runnables[i]=new CountingRunnable();
threads[i]=new Thread(runnables[i]);
threads[i].setPriority(priority);
threads[i].setName("PriorityThread_"+priority);
}
}
}
如果我让程序计数一分钟(NUM_MILLIS_TO_COUNT_FOR = 1*60*1000),那么我得到以下输出:
MIN_PRIORITY: 1
MAX_PRIORITY: 10
PriorityThread_1 has priority: 1 and count:12658044343
PriorityThread_2 has priority: 2 and count:19008431582
PriorityThread_3 has priority: 3 and count:30618946099
PriorityThread_4 has priority: 4 and count:34408365142
PriorityThread_5 has priority: 5 and count:36694025023
PriorityThread_6 has priority: 6 and count:40493710165
PriorityThread_7 has priority: 7 and count:42826305342
PriorityThread_8 has priority: 8 and count:42203891414
PriorityThread_9 has priority: 9 and count:43128747383
PriorityThread_10 has priority: 10 and count:43416371500
根据这一输出,优先事项似乎具有预期的影响!但是如果我使用"jstack"或"kill -s QUIT"生成一个线程转储,那么我得到以下输出,这意味着每个线程都具有相同的优先级(prio = 10):
"PriorityThread_10" prio=10 tid=0x00007ff7e406f800 nid=0x12e6 runnable [0x00007ff7e2562000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_9" prio=10 tid=0x00007ff7e406d800 nid=0x12e5 runnable [0x00007ff7e2663000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_8" prio=10 tid=0x00007ff7e406b000 nid=0x12e4 runnable [0x00007ff7e2764000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_7" prio=10 tid=0x00007ff7e4069000 nid=0x12e3 runnable [0x00007ff7e2865000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_6" prio=10 tid=0x00007ff7e4067000 nid=0x12e2 runnable [0x00007ff7e2966000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_5" prio=10 tid=0x00007ff7e4065000 nid=0x12e1 runnable [0x00007ff7e2a67000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_4" prio=10 tid=0x00007ff7e4063000 nid=0x12e0 runnable [0x00007ff7e2b68000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_3" prio=10 tid=0x00007ff7e4061000 nid=0x12df runnable [0x00007ff7e2c69000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_2" prio=10 tid=0x00007ff7e405d000 nid=0x12de runnable [0x00007ff7e2d6a000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
"PriorityThread_1" prio=10 tid=0x00007ff7e4049800 nid=0x12dd runnable [0x00007ff7e2e6b000]
java.lang.Thread.State: RUNNABLE
at ch.mypackage.CountingRunnable.run(CountingRunnable.java:17)
at java.lang.Thread.run(Thread.java:679)
如果我在Windows机器上执行相同的操作,根据我在此处找到的优先级映射,prio值是正确的值.
那么,这是jstack中的一个错误,还是我做错了什么？
如果我执行"top | grep java",我会得到以下内容:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3394 root 20 0 4444m 15m 8376 S 789 0.1 0:47.52 java
这意味着主线程的优先级为20,而"top -H | grep java"会产生以下输出:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3457 root 15 -5 4444m 15m 8384 R 99 0.1 0:08.60 java
3456 root 16 -4 4444m 15m 8384 R 97 0.1 0:08.41 java
3455 root 17 -3 4444m 15m 8384 R 93 0.1 0:08.42 java
3454 root 18 -2 4444m 15m 8384 R 97 0.1 0:08.27 java
3453 root 19 -1 4444m 15m 8384 R 97 0.1 0:07.50 java
3452 root 20 0 4444m 15m 8384 R 51 0.1 0:07.44 java
3451 root 21 1 4444m 15m 8384 R 35 0.1 0:04.83 java
3450 root 22 2 4444m 15m 8384 R 99 0.1 0:04.78 java
3449 root 23 3 4444m 15m 8384 R 95 0.1 0:07.47 java
3448 root 24 4 4444m 15m 8384 R 18 0.1 0:02.85 java
这表明java线程优先级确实影响了OS线程的优先级.
但是jstack在prio = 10中的值是10？它只是一个任意值吗？
Java 中的线程优先级是一个非常非常敏感的话题...您可以在 StackOverlow 上找到一篇有趣的文章： https: //stackoverflow.com/a/2170304/1343096
基本上尝试将您的优先级策略更改为 42 ：
-XX:ThreadPriorityPolicy=42
让我们知道它是否适合您！
您可以通过链接找到所有解释。