JVM調優(9)jstack定位死迴圈、執行緒阻塞、死鎖等問題
阿新 • • 發佈:2019-01-05
當我們執行java程式時,可能會出現死迴圈,IO阻塞,執行緒死鎖等問題,導致程式無法進行下去,但從程式碼上有無法確定問題出現的具體原因或者地方。可以使用JDK自帶的jstack工具去簡單定位;
死迴圈
程式如下:
/**
* @Author Ralph
* 死迴圈定位
*/
public class Test01 {
public static void main(String[] args) {
while(true){
}
}
}
等程式出現死迴圈時,可以使用jstack命令打印出日誌分析出具體原因地方,命令如下:
Ralph:~ allenlee$ jps
1144 Launcher
1145 Test01
284
1166 Jps
Ralph:~ allenlee$ jstack 1145
列印日誌如下:
2019-01-02 18:19:49
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.171-b11 mixed mode):
"Attach Listener" #10 daemon prio=9 os_prio=31 tid=0x00007fddde99a000 nid=0xa07 waiting on condition [0x0000000000000000]
java. lang.Thread.State: RUNNABLE
"Service Thread" #9 daemon prio=9 os_prio=31 tid=0x00007fdddd16e800 nid=0x3803 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread2" #8 daemon prio=9 os_prio=31 tid=0x00007fddde112000 nid=0x4403 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" #7 daemon prio=9 os_prio=31 tid=0x00007fdddd926800 nid=0x3703 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #6 daemon prio=9 os_prio=31 tid=0x00007fddde9a3000 nid=0x3503 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Monitor Ctrl-Break" #5 daemon prio=5 os_prio=31 tid=0x00007fddde10f000 nid=0x4703 runnable [0x000070000d33b000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
- locked <0x0000000795902cd8> (a java.io.InputStreamReader)
at java.io.InputStreamReader.read(InputStreamReader.java:184)
at java.io.BufferedReader.fill(BufferedReader.java:161)
at java.io.BufferedReader.readLine(BufferedReader.java:324)
- locked <0x0000000795902cd8> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(BufferedReader.java:389)
at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)
"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fdddd03c800 nid=0x3407 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fddde02c800 nid=0x2d03 in Object.wait() [0x000070000d0b2000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000795588ed0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
- locked <0x0000000795588ed0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:212)
"Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fddde000000 nid=0x5003 in Object.wait() [0x000070000cfaf000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000795586bf8> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x0000000795586bf8> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"main" #1 prio=5 os_prio=31 tid=0x00007fddde001800 nid=0x2903 runnable [0x000070000c99d000]
java.lang.Thread.State: RUNNABLE
at com.lyh.seckill.test.Test01.main(Test01.java:10)
"VM Thread" os_prio=31 tid=0x00007fdddd81c000 nid=0x5103 runnable
"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fdddd013800 nid=0x1f07 runnable
"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fdddd014800 nid=0x2203 runnable
"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fdddd015000 nid=0x2a03 runnable
"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fdddd015800 nid=0x5303 runnable
"VM Periodic Task Thread" os_prio=31 tid=0x00007fdddd16f000 nid=0x3903 waiting on condition
JNI global references: 15
從輸出的日誌中可以看到com.lyh.seckill.test.Test01.main(Test01.java:10)
,main執行緒,處於runnable狀態,在main方法的第10行,也就是我們死迴圈的位置。
死鎖
例子程式碼如下:
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* @Author Ralph
* 死鎖
*/
public class Test01 implements Runnable {
private Object obj1;
private Object obj2;
private int order;
public Test01(int order, Object obj1, Object obj2) {
this.order = order;
this.obj1 = obj1;
this.obj2 = obj2;
}
public void test1() throws InterruptedException {
synchronized (obj1) {
Thread.yield();
synchronized (obj2) {
System.out.println("test。。。");
}
}
}
public void test2() throws InterruptedException {
synchronized (obj2) {
Thread.yield();
synchronized (obj1) {
System.out.println("test。。。");
}
}
}
@Override
public void run() {
while (true) {
try {
if (this.order == 1) {
this.test1();
} else {
this.test2();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) throws InterruptedException {
Object obj1 = new Object();
Object obj2 = new Object();
ExecutorService ex = Executors.newFixedThreadPool(10);
// 起10個執行緒
for (int i = 0; i < 10; i++) {
int order = i % 2 == 0 ? 1 : 0;
ex.execute(new Test01(order, obj1, obj2));
}
}
}
先用jps找到PID,然後jstack命令檢視資訊