jps
需要用到j(luò)ps來顯示相關(guān)詳細(xì)信息整以。
命令格式：
jps [options ] [ hostid ]
[options]選項(xiàng) ：
-l：輸出啟動(dòng)jar的完全路徑名
-m：輸出main method的參數(shù)
-v：輸出jvm參數(shù)
https://blog.csdn.net/wisgood/article/details/38942449
CPU占用率過大
1.top命令查看當(dāng)前CPU情況
top -H -p2023
說明： -H 指顯示線程，-p 是指定進(jìn)程
2.可以看到CPU占用較高的線程斯嚎，記下PID （ 此處的PID即為線程ID標(biāo)識(shí)） 锣光，將其從十進(jìn)制轉(zhuǎn)成十六進(jìn)制表示
3.通過jstack命令獲取當(dāng)前進(jìn)程的所有線程棧捏卓，可暫時(shí)保存到一個(gè)文件tempfile.txt中：
jstack -l 2023 > tempfile.txt
2023是進(jìn)程id
4.在tempfile.txt中查找nid=0x7f1（2023的十六進(jìn)制）的線程
https://my.oschina.net/shipley/blog/520062
如何使用jstack分析線程狀態(tài) - 簡(jiǎn)書
頻繁 Full GC
thread dump鎖分析
下面對(duì)比一下synchronized和java.util.concurrent的區(qū)別
synchronized方式
[得到鎖]
state：RUNNABLE locked
[被阻塞]
state：BLOCKED waiting to lock
[調(diào)用wait]
state：WAITING waiting on
如何使用jstack分析線程狀態(tài) - 簡(jiǎn)書
java.util.concurrent方式
[得到鎖]
顯示waiting on condition和Locked ownable synchronizers
[被阻塞]
state：WAITING(parking) parking to wait for
[調(diào)用await]
state：WAITING parking to wait for
Java thread dump: Difference between “waiting to lock” and “parking to wait for”?
進(jìn)一步可以參考關(guān)于兩者區(qū)別丛忆。下面用例子來展示加鎖后兩者區(qū)別，都分別加了兩次鎖（加兩次鎖的原因是為更好展示stack）：
package com.tom;
import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
@Slf4j
public class LockTest {
Lock lock1 = new ReentrantLock(true);
Lock lock2 = new ReentrantLock(true);
Condition condition = lock1.newCondition();
Object objLock = new Object();
@Test
public void test() {
reentrantLock();
sync();
try {
Thread.sleep(100000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
void reentrantLock() {
Thread th = new Thread(new Runnable() {
public void run() {
lock1.lock();
try {
lock2.lock();
try {
try {
Thread.sleep(100000);
} catch (InterruptedException e) {
e.printStackTrace();
}
} finally {
lock2.unlock();
}
} finally {
lock1.unlock();
}
}
}, "reentrantLock");
th.start();
}
void sync() {
Thread th = new Thread(new Runnable() {
public void run() {
// 這個(gè)代碼是測(cè)試dump從哪開始記錄
int i = 0;
// 加鎖
doSync1();
}
}, "Sync");
th.start();
}
synchronized void doSync1() {
doSync2();
}
void doSync2() {
synchronized (objLock) {
try {
objLock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
線程stack
"Sync" #14 prio=5 os_prio=0 tid=0x000000001de3e800 nid=0x147f48 in Object.wait() [0x000000001e7be000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x0000000781025470> (a java.lang.Object) // 調(diào)用wait()后
at java.lang.Object.wait(Object.java:502)
at com.tom.LockTest.doSync2(LockTest.java:77)
- locked <0x0000000781025470> (a java.lang.Object) // 第2次加鎖
at com.tom.LockTest.doSync1(LockTest.java:71)
- locked <0x00000007810253d8> (a com.tom.LockTest) // 第1次加鎖
at com.tom.LockTest$2.run(LockTest.java:64)
at java.lang.Thread.run(Thread.java:745)
Locked ownable synchronizers:
- None
"reentrantLock" #13 prio=5 os_prio=0 tid=0x000000001dcc0800 nid=0x148a70 waiting on condition [0x000000001ccfe000] // 可以看到這里是condition
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at com.tom.LockTest$1.run(LockTest.java:40)
at java.lang.Thread.run(Thread.java:745)
Locked ownable synchronizers: // 2次加鎖盖袭，所以持有2個(gè)鎖
- <0x0000000781025408> (a java.util.concurrent.locks.ReentrantLock$FairSync)
- <0x0000000781025438> (a java.util.concurrent.locks.ReentrantLock$FairSync)
關(guān)于synchronized的線程stack要說明的是：
線程stack只顯示直接調(diào)用synchronized的方法名失暂，擁有synchronized的方法并不顯示。拿上面的代碼舉例苍凛，doSync1調(diào)用方法doSync2趣席，doSync2含有同步代碼塊，那么stack只會(huì)顯示：
- locked <0x0000000781025470> (a java.lang.Object) // 第2次加鎖
at com.tom.LockTest.doSync1(LockTest.java:71)
不會(huì)顯示doSync2
FAQ
Q：
synchronized加鎖后再調(diào)用wait醇蝴，線程stack是否會(huì)顯示當(dāng)前已解鎖
A：不會(huì)宣肚。雖然事實(shí)上這時(shí)該線程已解鎖，但是stack顯示的該線程先持久對(duì)象鎖悠栓，然后waiting on該鎖（stack顯示的是線程對(duì)鎖的類似操作歷史）
其他命令
ulimit -a查看我們系統(tǒng)的所有限制
https://blog.csdn.net/gatieme/article/details/51058797
