Weblogic OutOfMemory exception的誤解 -- thread limitation

標籤：loop   nat   資源   超出   strong   imu   except   rar   inux   

不是全部的OutofMemory exception都是記憶體問題。。。

前幾天有個客戶的site報了下面錯誤：

[ERROR][thread ] Could not start thread Timer-72025. Resource temporarily unavailableException in thread "Timer-72024" java.lang.OutOfMemoryError: Resource temporarily unavailable in tsStartJavaThread (lifecycle.c:1097).Attempting to allocate 2G bytesThere is insufficient native memory for the JavaRuntime Environment to continue.Possible reasons:  The system is out of physical RAM or swap space  In 32 bit mode, the process size limit was hitPossible solutions:  Reduce memory load on the system  Increase physical memory or swap space  Check if swap backing store is full  Use 64 bit Java on a 64 bit OS  Decrease Java heap size (-Xmx/-Xms)  Decrease number of Java threads  Decrease Java thread stack sizes (-Xss)  Disable compressed references (-XXcompressedRefs=false)                at java.lang.Thread.start0(Native Method)                at java.lang.Thread.start(Thread.java:640)                at java.util.Timer.<init>(Timer.java:137)                at java.util.Timer.<init>(Timer.java:106)                at ......                at java.util.TimerThread.mainLoop(Timer.java:512)                at java.util.TimerThread.run(Timer.java:462)

第一反應以為是記憶體不足，於是dump了heap回來看。發現系統僅僅佔用了80M的記憶體，遠遠系統記憶體綽綽有餘，那麼為啥會出現這樣的情況呢？查看了出錯的代碼。發現代碼啟動了非常多的線程，遂想起曾經遇到過類似的問題，weblogic裡面啟動的線程太多。超出了linux的最大限制，也是會出這個看起來記憶體流失的日誌。查看系統的限制：

[email protected] limits.d # ulimit -acore file size          (blocks, -c) 0data seg size           (kbytes, -d) unlimitedscheduling priority             (-e) 0file size               (blocks, -f) unlimitedpending signals                 (-i) 38610max locked memory       (kbytes, -l) 64max memory size         (kbytes, -m) unlimitedopen files                      (-n) 8192pipe size            (512 bytes, -p) 8POSIX message queues     (bytes, -q) 819200real-time priority              (-r) 0stack size              (kbytes, -s) 10240cpu time               (seconds, -t) unlimitedmax user processes              (-u) 1024virtual memory          (kbytes, -v) unlimitedfile locks                      (-x) unlimited

發現最大的進程數是1024，注意：linux裡面計算線程和進程是用一樣計算的，這裡說的max user processes是包含線程的。

使用下面代碼重現問題：

public class ThreadExample {    public static void main(String[] args){        System.out.println(Thread.currentThread().getName());        for(int i=0; i< 2048; i++){            new Thread("" + i){                public void run(){                    System.out.println(Thread.currentThread().getName() + " running");                    try {                        Thread.sleep(60000);                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                    System.out.println(Thread.currentThread().getName() + " ending");                }            }.start();        }    }}

運行和輸出：

[email protected]_Z1 etmdaha # su -p occas -c "/opt/jrockit-jdk/bin/java ThreadExample"Main Thread0 running5 running//836 running[ERROR][thread ] Could not start thread 837. Resource temporarily unavailableException in thread "Main Thread" java.lang.OutOfMemoryError: Resource temporarily unavailable in tsStartJavaThread (lifecycle.c:1096).Attempting to allocate 3G bytesThere is insufficient native memory for the JavaRuntime Environment to continue.Possible reasons:  The system is out of physical RAM or swap space  In 32 bit mode, the process size limit was hitPossible solutions:  <strong>Reduce memory load on the system  Increase physical memory or swap space  Check if swap backing store is full  Use 64 bit Java on a 64 bit OS  Decrease Java heap size (-Xmx/-Xms)  Decrease number of Java threads  Decrease Java thread stack sizes (-Xss)  Disable compressed references (-XXcompressedRefs=false)</strong>        at java.lang.Thread.start0(Native Method)        at java.lang.Thread.start(Thread.java:640)        at ThreadExample.main(ThreadExample.java:6)

linux系統資源有各種限制：記憶體限制。棧限制，檔案數目限制，線程限制。要小心陷進這些問題。

# ulimit -acore file size          (blocks, -c) 0data seg size           (kbytes, -d) unlimitedscheduling priority             (-e) 0file size               (blocks, -f) unlimitedpending signals                 (-i) 79010max locked memory       (kbytes, -l) 64max memory size         (kbytes, -m) unlimitedopen files                      (-n) 1024pipe size            (512 bytes, -p) 8POSIX message queues     (bytes, -q) 819200real-time priority              (-r) 0stack size              (kbytes, -s) 10240cpu time               (seconds, -t) unlimitedmax user processes              (-u) 1024virtual memory          (kbytes, -v) unlimitedfile locks                      (-x) unlimited

這裡有兩篇非常好的文章：

http://people.redhat.com/alikins/system_tuning.html#threads

http://kavassalis.com/2011/03/linux-and-the-maximum-number-of-processes-threads/

Weblogic OutOfMemory exception的誤解 -- thread limitation