Siete, punto muerto
1. El problema lleva a
class DeadLock {
private final Object LOCK_A = new Object();
private final Object LOCK_B = new Object();
public void methodA() {
synchronized (LOCK_A) {
try {
Thread.sleep(1000); } catch (InterruptedException e) {
e.printStackTrace(); }
System.out.println(Thread.currentThread().getName() + "获取锁A，尝试获取锁B");
synchronized (LOCK_B) {
}
}
}
public void methodB() {
synchronized (LOCK_B) {
try {
Thread.sleep(1000); } catch (InterruptedException e) {
e.printStackTrace(); }
System.out.println(Thread.currentThread().getName() + "获取锁B，尝试获取锁A");
synchronized (LOCK_A) {
}
}
}
}
public class DeadLockTest {
public static void main(String[] args) {
DeadLock dl = new DeadLock();
new Thread(dl::methodA, "线程A").start();
new Thread(dl::methodB, "线程B").start();
}
}
Ejecute el código, puede ver que el programa está bloqueado y no se puede ejecutar
2. La causa del problema
Múltiples subprocesos que han adquirido bloqueos, cuando se intenta adquirir bloqueos ya mantenidos por otros subprocesos, se produce un interbloqueo
3. Cómo solucionar problemas
Utilice los dos comandos que vienen con Java: jpsyjstack
Primero ejecute el comando: jps -lpara obtener el ID de proceso del programa Java que se está ejecutando
Luego ejecute el comando : jstack -l 进程ID, puede ver la siguiente información similar
"线程B" #12 prio=5 os_prio=0 tid=0x000000001657a800 nid=0x65c waiting for monitor entry [0x0000000016d8f000]
java.lang.Thread.State: BLOCKED (on object monitor)
at DeadLock.methodB(DeadLockTest.java:21)
- waiting to lock <0x00000000f57e2568> (a java.lang.Object)
- locked <0x00000000f57e2578> (a java.lang.Object)
at DeadLockTest$$Lambda$2/205797316.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Locked ownable synchronizers:
- None
"线程A" #11 prio=5 os_prio=0 tid=0x0000000016579800 nid=0x4f4 waiting for monitor entry [0x0000000016c8e000]
java.lang.Thread.State: BLOCKED (on object monitor)
at DeadLock.methodA(DeadLockTest.java:11)
- waiting to lock <0x00000000f57e2578> (a java.lang.Object)
- locked <0x00000000f57e2568> (a java.lang.Object)
at DeadLockTest$$Lambda$1/1637070917.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Locked ownable synchronizers:
- None
Found one Java-level deadlock:
=============================
"线程B":
waiting to lock monitor 0x0000000002ffde38 (object 0x00000000f57e2568, a java.lang.Object),
which is held by "线程A"
"线程A":
waiting to lock monitor 0x0000000002ffb658 (object 0x00000000f57e2578, a java.lang.Object),
which is held by "线程B"
Java stack information for the threads listed above:
===================================================
"线程B":
at DeadLock.methodB(DeadLockTestjava:21)
- waiting to lock <0x00000000f57e2568> (a java.lang.Object)
- locked <0x00000000f57e2578> (a java.lang.Object)
at DeadLockTest$$Lambda$2/205797316.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
"线程A":
at DeadLock.methodA(DeadLockTestjava:11)
- waiting to lock <0x00000000f57e2578> (a java.lang.Object)
- locked <0x00000000f57e2568> (a java.lang.Object)
at DeadLockTest$$Lambda$1/1637070917.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Found 1 deadlock.
La ubicación del interbloqueo está claramente marcada