交叉锁不仅自己写的代码会出现,如果使用某个框架或者开源库,由于对源码 API 的不熟悉,很有可能也会引起死锁,这种情况出现死锁后,排查的困难则要高于前者,所以在使用框架或者开源库的时候要做到了如指掌。
package concurrent;
public class DeadLock {
private final Object mutexRead = new Object();
private final Object mutexWrite = new Object();
public void read() {
synchronized (mutexRead) {
System.out.println(Thread.currentThread().getName() + " get READ lock");
synchronized (mutexWrite) {
System.out.println(Thread.currentThread().getName() + " get write lock");
}
System.out.println(Thread.currentThread().getName() + " release write lock");
}
System.out.println(Thread.currentThread().getName() + " release READ lock");
}
public void write() {
synchronized (mutexWrite) {
System.out.println(Thread.currentThread().getName() + " get write lock");
synchronized (mutexRead) {
System.out.println(Thread.currentThread().getName() + " get READ lock");
}
System.out.println(Thread.currentThread().getName() + " release READ lock");
}
System.out.println(Thread.currentThread().getName() + " release write lock");
}
public static void main(String[] args) {
final DeadLock deadLock = new DeadLock();
new Thread(() -> {
while (true) {
deadLock.read();
}
}, "READ-THREAD").start();
new Thread(() -> {
while (true) {
deadLock.write();
}
}, "WRITE-THREAD").start();
}
}
READ-THREAD get READ lock
READ-THREAD get write lock
READ-THREAD release write lock
READ-THREAD release READ lock
READ-THREAD get READ lock
READ-THREAD get write lock
READ-THREAD release write lock
READ-THREAD release READ lock
READ-THREAD get READ lock
READ-THREAD get write lock
READ-THREAD release write lock
READ-THREAD release READ lock
READ-THREAD get READ lock
WRITE-THREAD get write lock
这种交叉锁导致的程序死锁,可以使用 jstack 工具或 jconsole 工具。下面是定位过程,jps 和 jstack 两个命令就能搞定。
E:\JVMDemo\demo2022\target\classes>jps
11024 Launcher
7872
11384 RemoteMavenServer36
14440 Jps
5736 DeadLock
E:\JVMDemo\demo2022\target\classes>Jstack -l 5736
2022-03-05 09:31:14
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.251-b08 mixed mode):
"DestroyJavaVM" #14 prio=5 os_prio=0 tid=0x0000000002853800 nid=0x27c0 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"WRITE-THREAD" #13 prio=5 os_prio=0 tid=0x000000001e998800 nid=0x2a30 waiting for monitor entry [0x000000001f1ff000]
java.lang.Thread.State: BLOCKED (on object monitor)
at concurrent.DeadLock.write(DeadLock.java:22)
- waiting to lock <0x0000000770748c18> (a java.lang.Object)
- locked <0x0000000770748c28> (a java.lang.Object)
at concurrent.DeadLock.lambda$main$1(DeadLock.java:39)
at concurrent.DeadLock$$Lambda$2/1028214719.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Locked ownable synchronizers:
- None
"READ-THREAD" #12 prio=5 os_prio=0 tid=0x000000001e995800 nid=0xa34 waiting for monitor entry [0x000000001f0fe000]
java.lang.Thread.State: BLOCKED (on object monitor)
at concurrent.DeadLock.read(DeadLock.java:11)
- waiting to lock <0x0000000770748c28> (a java.lang.Object)
- locked <0x0000000770748c18> (a java.lang.Object)
at concurrent.DeadLock.lambda$main$0(DeadLock.java:33)
at concurrent.DeadLock$$Lambda$1/1338668845.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Locked ownable synchronizers:
- None
"Service Thread" #11 daemon prio=9 os_prio=0 tid=0x000000001daa6800 nid=0x3294 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"C1 CompilerThread3" #10 daemon prio=9 os_prio=2 tid=0x000000001dac4000 nid=0x1d58 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"C2 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x000000001dac3800 nid=0x458 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001dac2800 nid=0x3500 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x000000001dabc800 nid=0x1c34 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x000000001daa5000 nid=0x1790 runnable [0x000000001e1fe000]
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 <0x0000000770828970> (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 <0x0000000770828970> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(BufferedReader.java:389)
at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:61)
Locked ownable synchronizers:
- None
"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001d938000 nid=0x2c74 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001d8e5000 nid=0x381c runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x000000000294b800 nid=0x36b8 in Object.wait() [0x000000001de9e000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000770588ee0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
- locked <0x0000000770588ee0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
Locked ownable synchronizers:
- None
"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001d8c0800 nid=0x1bc4 in Object.wait() [0x000000001dd9f000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000770586c00> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x0000000770586c00> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
Locked ownable synchronizers:
- None
"VM Thread" os_prio=2 tid=0x000000001baca000 nid=0x8f0 runnable
"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002869800 nid=0x183c runnable
"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x000000000286b000 nid=0x3280 runnable
"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x000000000286c800 nid=0x22e8 runnable
"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x000000000286f000 nid=0x19ac runnable
"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002871800 nid=0x2cb8 runnable
"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002872800 nid=0x2150 runnable
"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002875800 nid=0x1524 runnable
"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002877000 nid=0x3a68 runnable
"VM Periodic Task Thread" os_prio=2 tid=0x000000001db4b000 nid=0x338c waiting on condition
JNI global references: 316
Found one Java-level deadlock:
=============================
"WRITE-THREAD":
waiting to lock monitor 0x000000001bad3708 (object 0x0000000770748c18, a java.lang.Object),
which is held by "READ-THREAD"
"READ-THREAD":
waiting to lock monitor 0x000000001bad2268 (object 0x0000000770748c28, a java.lang.Object),
which is held by "WRITE-THREAD"
Java stack information for the threads listed above:
===================================================
"WRITE-THREAD":
at concurrent.DeadLock.write(DeadLock.java:22)
- waiting to lock <0x0000000770748c18> (a java.lang.Object)
- locked <0x0000000770748c28> (a java.lang.Object)
at concurrent.DeadLock.lambda$main$1(DeadLock.java:39)
at concurrent.DeadLock$$Lambda$2/1028214719.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
"READ-THREAD":
at concurrent.DeadLock.read(DeadLock.java:11)
- waiting to lock <0x0000000770748c28> (a java.lang.Object)
- locked <0x0000000770748c18> (a java.lang.Object)
at concurrent.DeadLock.lambda$main$0(DeadLock.java:33)
at concurrent.DeadLock$$Lambda$1/1338668845.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Found 1 deadlock.
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