java CPU100%占用

bootsrc · bootsrc · commit 5f9785202e18 · 2019-04-10T14:58:43.000+08:00
diff --git a/README.md b/README.md
@@ -19,6 +19,8 @@ Senior Java engineer interview exams in 2019
     * [zookeeper选举机制](https://www.linuxidc.com/Linux/2018-09/154117.htm)
 
     * [Redis集群方式有哪几种](readme/redis-cluster-strategies.md)
+    
+    * [如何排查Java的CPU性能问题-CPU100%占用](readme/cpu100percent.md)
 
 
 <hr/>
diff --git a/code/CpuTest.class b/code/CpuTest.class
diff --git a/code/CpuTest.java b/code/CpuTest.java
@@ -0,0 +1,14 @@
+public class CpuTest {
+    public static void main(String[] args) {
+        int i= 0;
+
+        while (true) {
+            i++;
+//            if (i == Integer.MAX_VALUE) {
+////                System.out.println("--reset---");
+//                i = 0;
+//            }
+        }
+
+    }
+}
diff --git a/readme/cpu100percent.md b/readme/cpu100percent.md
@@ -0,0 +1,116 @@
+# 如何排查Java的CPU性能问题-CPU100%占用
+
+## 排查步骤
+
+例如一个java进程的cpu占用达到99.3%
+
+```text
+top - 14:56:39 up 199 days,  4:55,  3 users,  load average: 2.24, 2.35, 2.27
+Tasks:  81 total,   1 running,  76 sleeping,   4 stopped,   0 zombie
+%Cpu(s):100.0 us,  0.0 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
+KiB Mem :  1883492 total,   100904 free,   968764 used,   813824 buff/cache
+KiB Swap:        0 total,        0 free,        0 used.   727152 avail Mem 
+
+  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND                                                                                  
+ 8999 root      20   0 2460600  17060  10116 S 99.3  0.9  31:51.17 java                                                                                     
+23996 root       0 -20  138996  17416   6260 S  0.3  0.9 375:12.90 AliYunDun                                                                                
+    1 root      20   0  190708   2492   1284 S  0.0  0.1   1:32.14 systemd                                                                                  
+    2 root      20   0       0      0      0 S  0.0  0.0   0:00.01 kthreadd                                                                                 
+    3 root      20   0       0      0      0 S  0.0  0.0   0:52.57 ksoftirqd/0                                                                              
+    5 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kworker/0:0H                                                                             
+    7 root      rt   0       0      0      0 S  0.0  0.0   0:00.00 migration/0         
+```
+
+ 1.top 
+找到占用cpu太高的java进程的pid
+假如是8999
+
+2.查看pid对应进程的线程的资源占用情况
+```text
+ps -mp 8999 -o THREAD,tid,time
+```
+
+例如
+```text
+[root@iz8vb3nxwmck3z1ruwn8euz 9000]# ps -mp 8999 -o THREAD,tid,time
+USER     %CPU PRI SCNT WCHAN  USER SYSTEM   TID     TIME
+root      0.0   -    - -         -      -     - 00:37:34
+root      0.0  19    - futex_    -      -  8999 00:00:00
+root      0.0  19    - futex_    -      -  9000 00:00:05
+root      0.0  19    - futex_    -      -  9001 00:01:27
+```
+
+假如最高的tid是9000 (线程id)
+
+3.tid转化成十六进制
+```text
+printf "%x\n" 9000
+2328
+```
+
+4.jstack查看线程栈日志
+例如
+
+```text
+[root@iz8vb3nxwmck3z1ruwn8euz 9000]# jstack 8999 |grep 2328 -A 30
+"DestroyJavaVM" #36 prio=5 os_prio=0 tid=0x00007f5e18009800 nid=0x2328 waiting on condition [0x0000000000000000]
+   java.lang.Thread.State: RUNNABLE
+
+"pool-3-thread-3" #35 prio=5 os_prio=0 tid=0x00007f5dec05b000 nid=0x234c waiting on condition [0x00007f5de59ea000]
+   java.lang.Thread.State: WAITING (parking)
+	at sun.misc.Unsafe.park(Native Method)
+	- parking to wait for  <0x00000000f56abee8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
+	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
+	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
+	at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
+	at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
+	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
+	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
+	at java.lang.Thread.run(Thread.java:748)
+```
+
+命中的位置是
+nid=0x2328
+
+nid指的是native thread id (linux native light weight process id)
+这个日志会显示报错的java代码的那一行。
+
+关于grep里的参数"-A"的说明
+-A<显示列数> 除了显示符合范本样式的那一行之外，并显示该行之后的内容。
+
+##  测试程序
+程序的cpu占用达到80%～100%这种情况，一般可能发送在大量的for循环或者while循环中(也可能是死循环中的反复计算)
+
+demo程序见[CpuTest.java](/code/CpuTest.java)
+
+贴出代码
+```java
+public class CpuTest {
+    public static void main(String[] args) {
+        int i= 0;
+
+        while (true) {
+            i++;
+//            if (i == Integer.MAX_VALUE) {
+////                System.out.println("--reset---");
+//                i = 0;
+//            }
+        }
+
+    }
+}
+
+```
+
+先编译程序，然后运行CpuTest.class，命令如下
+```shell
+#cd code/
+
+#javac CpuTest.java 
+#ls
+CpuTest.class   CpuTest.java
+
+#java CpuTest
+```
+
+然后用top命令可以看到有个java进程cpu占用特别大。
