1.診斷CPU佔用過高
[root@master ~]# nohup java -jar JvmProject.jar & // 有問題的java程式
[1] 1627
[root@master ~]# nohup: ignoring input and appending output to ‘nohup.out’
1.1使用top命令來檢視是那個程式佔用CPU過高
top - 08:57:03 up 25 min, 1 user, load average: 0.49, 0.77, 0.58
Tasks: 104 total, 1 running, 103 sleeping, 0 stopped, 0 zombie
%Cpu(s): 99.7 us, 0.3 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 995464 total, 359540 free, 290336 used, 345588 buff/cache
KiB Swap: 1048572 total, 1048572 free, 0 used. 557932 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1710 root 20 0 2241412 28948 11752 S 99.9 2.9 0:09.24 java
1655 root 20 0 0 0 0 S 0.3 0.0 0:00.28 kworker/0:1
1 root 20 0 125484 3892 2584 S 0.0 0.4 0:01.38 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
4 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
5 root 20 0 0 0 0 S 0.0 0.0 0:00.07 kworker/u256:0
6 root 20 0 0 0 0 S 0.0 0.0 0:00.06 ksoftirqd/0
1.2使用ps -H -eo pid,tid,%cpu | grep 程式ID(用PS命令進一步定位是哪個執行緒引起的cpu佔用過高)
[root@master ~]# ps -H -eo pid,tid,%cpu | grep 1790
1790 1790 99.5
1.3.jstack 程式ID 檢視該程式中的所有java執行緒資訊
透過程式的id與jstack的結果進行匹配，由於linux中程式id是10進位制而java中是16進位制所以需要使用進位制轉換，程式1790+10轉換成16進製為708 (在虛擬機器中不知道什麼原因pid+10 = tid)
[root@master ~]# jstack 1790
2023-01-10 09:05:45
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.202-b08 mixed mode):
"Attach Listener" #12 daemon prio=9 os_prio=0 tid=0x00007f1d64001000 nid=0x72a waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE
"DestroyJavaVM" #11 prio=5 os_prio=0 tid=0x00007f1d8c009000 nid=0x6ff waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"thread3" #10 prio=5 os_prio=0 tid=0x00007f1d8c140000 nid=0x70a waiting on condition [0x00007f1d6968c000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at com.aircoinst.Demo1_6.lambda$main$2(Demo1_6.java:24)
at com.aircoinst.Demo1_6$$Lambda$3/250421012.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
"thread2" #9 prio=5 os_prio=0 tid=0x00007f1d8c13e000 nid=0x709 waiting on condition [0x00007f1d6978d000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at com.aircoinst.Demo1_6.lambda$main$1(Demo1_6.java:15)
at com.aircoinst.Demo1_6$$Lambda$2/455659002.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
"thread1" #8 prio=5 os_prio=0 tid=0x00007f1d8c13c000 nid=0x708 runnable [0x00007f1d6988e000]
java.lang.Thread.State: RUNNABLE
at com.aircoinst.Demo1_6.lambda$main$0(Demo1_6.java:7) # 該處就是CPU佔用過高問題所在(問題程式碼在第七行)
at com.aircoinst.Demo1_6$$Lambda$1/1406718218.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
"Service Thread" #7 daemon prio=9 os_prio=0 tid=0x00007f1d8c0db800 nid=0x706 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007f1d8c0d8800 nid=0x705 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007f1d8c0d6800 nid=0x704 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f1d8c0d4800 nid=0x703 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f1d8c0a1800 nid=0x702 in Object.wait() [0x00007f1d7c422000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000000f0c08ed0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
- locked <0x00000000f0c08ed0> (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)
"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007f1d8c09e800 nid=0x701 in Object.wait() [0x00007f1d7c523000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000000f0c06bf8> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x00000000f0c06bf8> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"VM Thread" os_prio=0 tid=0x00007f1d8c095000 nid=0x700 runnable
"VM Periodic Task Thread" os_prio=0 tid=0x00007f1d8c0de800 nid=0x707 waiting on condition
JNI global references: 311
紅色框內就是問題程式碼，所以該問題可以根據執行緒id找到有問題的執行緒，進一步定位到問題程式碼的原始碼行號，進行問題分析。
2.程式執行很長時間沒有結果
[root@master ~]# nohup java -jar JvmProject.jar &
[1] 1901
[root@master ~]# nohup: ignoring input and appending output to ‘nohup.out’
# 該地方沒有程式輸出,一直為卡死狀態
[root@master ~]#
2.1 使用jps命令查詢程式資訊，程式id為1901
[root@master ~]# jps
1913 Jps
1901 jar
2.2 使用jstack 程式id命令檢視所有執行緒資訊
[root@master ~]# jstack 1901
2023-01-10 09:25:28
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.202-b08 mixed mode):
"Attach Listener" #11 daemon prio=9 os_prio=0 tid=0x00007fde70001000 nid=0x78d waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"DestroyJavaVM" #10 prio=5 os_prio=0 tid=0x00007fde9c009000 nid=0x76e waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
....
....
Found one Java-level deadlock: # 產生了死鎖
=============================
"Thread-1":
waiting to lock monitor 0x00007fde7c004e28 (object 0x00000000f0c674c0, a com.aircoinst.A),
which is held by "Thread-0"
"Thread-0":
waiting to lock monitor 0x00007fde7c0062c8 (object 0x00000000f0c68a80, a com.aircoinst.B),
which is held by "Thread-1"
Java stack information for the threads listed above:
===================================================
"Thread-1":
at com.aircoinst.Demo1_7.lambda$main$1(Demo1_7.java:35) # 死鎖問題程式碼行
- waiting to lock <0x00000000f0c674c0> (a com.aircoinst.A) # 等待A物件的鎖
- locked <0x00000000f0c68a80> (a com.aircoinst.B) # 當前鎖住了B物件
at com.aircoinst.Demo1_7$$Lambda$2/295530567.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
"Thread-0":
at com.aircoinst.Demo1_7.lambda$main$0(Demo1_7.java:27) # 死鎖問題程式碼行
- waiting to lock <0x00000000f0c68a80> (a com.aircoinst.B) # 等待B物件的鎖
- locked <0x00000000f0c674c0> (a com.aircoinst.A) # 當前鎖住了A物件
at com.aircoinst.Demo1_7$$Lambda$1/250421012.run(Unknown Source)
at java.lang.Thread.run(Thread.java:748)
Found 1 deadlock.
對比原始碼，發現執行緒1與執行緒2同時發生了死鎖，造成了相A,B物件互等待釋放
