https://docs.oracle.com/javase/tutorial/essential/concurrency/deadlock.htmlの簡単な例
public class Deadlock {
public static void printMessage(String message) {
System.out.println(String.format("%s %s ", Thread.currentThread().getName(), message));
}
private static class Friend {
private String name;
public Friend(String name) {
this.name = name;
}
public void bow(Friend friend) {
printMessage("Acquiring lock on " + this.name);
synchronized(this) {
printMessage("Acquired lock on " + this.name);
printMessage(name + " bows " + friend.name);
friend.bowBack(this);
}
}
public void bowBack(Friend friend) {
printMessage("Acquiring lock on " + this.name);
synchronized (this) {
printMessage("Acquired lock on " + this.name);
printMessage(friend.name + " bows back");
}
}
}
public static void main(String[] args) throws InterruptedException {
Friend one = new Friend("one");
Friend two = new Friend("two");
new Thread(new Runnable() {
@Override
public void run() {
one.bow(two);
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
two.bow(one);
}
}).start();
}
}
出力:
Thread-0 Acquiring lock on one
Thread-1 Acquiring lock on two
Thread-0 Acquired lock on one
Thread-1 Acquired lock on two
Thread-1 two bows one
Thread-0 one bows two
Thread-1 Acquiring lock on one
Thread-0 Acquiring lock on two
スレッドダンプ:
2016-03-14 12:20:09
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.74-b02 mixed mode):
"DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x00007f472400a000 nid=0x3783 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Thread-1" #12 prio=5 os_prio=0 tid=0x00007f472420d800 nid=0x37a3 waiting for monitor entry [0x00007f46e89a5000]
java.lang.Thread.State: BLOCKED (on object monitor)
at com.anantha.algorithms.ThreadJoin$Friend.bowBack(ThreadJoin.java:102)
- waiting to lock <0x000000076d0583a0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$Friend.bow(ThreadJoin.java:92)
- locked <0x000000076d0583e0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$2.run(ThreadJoin.java:141)
at java.lang.Thread.run(Thread.java:745)
"Thread-0" #11 prio=5 os_prio=0 tid=0x00007f472420b800 nid=0x37a2 waiting for monitor entry [0x00007f46e8aa6000]
java.lang.Thread.State: BLOCKED (on object monitor)
at com.anantha.algorithms.ThreadJoin$Friend.bowBack(ThreadJoin.java:102)
- waiting to lock <0x000000076d0583e0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$Friend.bow(ThreadJoin.java:92)
- locked <0x000000076d0583a0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$1.run(ThreadJoin.java:134)
at java.lang.Thread.run(Thread.java:745)
"Monitor Ctrl-Break" #10 daemon prio=5 os_prio=0 tid=0x00007f4724211000 nid=0x37a1 runnable [0x00007f46e8def000]
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:170)
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 <0x000000076d20afb8> (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 <0x000000076d20afb8> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(BufferedReader.java:389)
at com.intellij.rt.execution.application.AppMain$1.run(AppMain.java:93)
at java.lang.Thread.run(Thread.java:745)
"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x00007f47240c9800 nid=0x3794 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread3" #8 daemon prio=9 os_prio=0 tid=0x00007f47240c6800 nid=0x3793 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread2" #7 daemon prio=9 os_prio=0 tid=0x00007f47240c4000 nid=0x3792 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007f47240c2800 nid=0x3791 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007f47240bf800 nid=0x3790 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f47240be000 nid=0x378f waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f472408c000 nid=0x378e in Object.wait() [0x00007f46e98c5000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x000000076cf88ee0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
- locked <0x000000076cf88ee0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)
"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007f4724087800 nid=0x378d in Object.wait() [0x00007f46e99c6000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x000000076cf86b50> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x000000076cf86b50> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"VM Thread" os_prio=0 tid=0x00007f4724080000 nid=0x378c runnable
"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007f472401f000 nid=0x3784 runnable
"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007f4724021000 nid=0x3785 runnable
"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00007f4724022800 nid=0x3786 runnable
"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00007f4724024800 nid=0x3787 runnable
"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x00007f4724026000 nid=0x3788 runnable
"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x00007f4724028000 nid=0x3789 runnable
"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x00007f4724029800 nid=0x378a runnable
"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x00007f472402b800 nid=0x378b runnable
"VM Periodic Task Thread" os_prio=0 tid=0x00007f47240cc800 nid=0x3795 waiting on condition
JNI global references: 16
Found one Java-level deadlock:
=============================
"Thread-1":
waiting to lock monitor 0x00007f46dc003f08 (object 0x000000076d0583a0, a com.anantha.algorithms.ThreadJoin$Friend),
which is held by "Thread-0"
"Thread-0":
waiting to lock monitor 0x00007f46dc006008 (object 0x000000076d0583e0, a com.anantha.algorithms.ThreadJoin$Friend),
which is held by "Thread-1"
Java stack information for the threads listed above:
===================================================
"Thread-1":
at com.anantha.algorithms.ThreadJoin$Friend.bowBack(ThreadJoin.java:102)
- waiting to lock <0x000000076d0583a0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$Friend.bow(ThreadJoin.java:92)
- locked <0x000000076d0583e0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$2.run(ThreadJoin.java:141)
at java.lang.Thread.run(Thread.java:745)
"Thread-0":
at com.anantha.algorithms.ThreadJoin$Friend.bowBack(ThreadJoin.java:102)
- waiting to lock <0x000000076d0583e0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$Friend.bow(ThreadJoin.java:92)
- locked <0x000000076d0583a0> (a com.anantha.algorithms.ThreadJoin$Friend)
at com.anantha.algorithms.ThreadJoin$1.run(ThreadJoin.java:134)
at java.lang.Thread.run(Thread.java:745)
Found 1 deadlock.
Heap
PSYoungGen total 74752K, used 9032K [0x000000076cf80000, 0x0000000772280000, 0x00000007c0000000)
eden space 64512K, 14% used [0x000000076cf80000,0x000000076d8520e8,0x0000000770e80000)
from space 10240K, 0% used [0x0000000771880000,0x0000000771880000,0x0000000772280000)
to space 10240K, 0% used [0x0000000770e80000,0x0000000770e80000,0x0000000771880000)
ParOldGen total 171008K, used 0K [0x00000006c6e00000, 0x00000006d1500000, 0x000000076cf80000)
object space 171008K, 0% used [0x00000006c6e00000,0x00000006c6e00000,0x00000006d1500000)
Metaspace used 3183K, capacity 4500K, committed 4864K, reserved 1056768K
class space used 352K, capacity 388K, committed 512K, reserved 1048576K