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VM最多能创建多少个线程: unable to create new native thread

原创 Java 作者:xiaoyan5686670 时间:2015-12-19 14:03:47 0 删除 编辑

转载:http://ju.outofmemory.cn/entry/74763
有应用报出这样的异常“java.lang.OutOfMemoryError: unable to create new native thread”。甚至机器上执行shell命令也会报”-bash: fork: Resource temporarily unavailable”异常。机器上的其他应用如hadoop也会受影响:

-08-21 20:15:48,496 FATAL org.apache.hadoop.yarn.event.AsyncDispatcher: Error in dispatcher thread
java.lang.OutOfMemoryError: unable to create new native thread
        at java.lang.Thread.start0(Native Method) at java.lang.Thread.start(Thread.java:640) at org.apache.hadoop.yarn.server.nodemanager.containermanager.localizer. ResourceLocalizationService$LocalizerTracker.handle(ResourceLocalizationService.java:524) at org.apache.hadoop.yarn.server.nodemanager.containermanager.localizer. ResourceLocalizationService$LocalizerTracker.handle(ResourceLocalizationService.java:456) at org.apache.hadoop.yarn.event.AsyncDispatcher.dispatch(AsyncDispatcher.java:128) at org.apache.hadoop.yarn.event.AsyncDispatcher$1.run(AsyncDispatcher.java:77) at java.lang.Thread.run(Thread.java:662) -08-21 20:15:48,497 INFO org.apache.hadoop.yarn.event.AsyncDispatcher: Exiting, bbye..

一看以为内存不够导致无法创建新的线程,但是观察机器上的内存还有空闲,猜测是哪个地方对线程创建有限制。

首先需要排除操作系统对线程创建数的限制,参考:《JVM中可生成的最大Thread数量》一文,设置操作系统可以支持创建10万个线程:

echo "100000" > /proc/sys/kernel/threads-max 
echo "100000" > /proc/sys/kernel/pid_max (默认32768 echo "200000" > /proc/sys/vm/max_map_count (默认65530 ulimit -u unlimited (设置max user processes的值)

当前测试环境为:

[admin@bufer108081.tbc ~]$ uname -a Linux bufer108081.tbc 2.6.32-220.23.2.ali927.el5.x86_64 #1 SMP Mon Jan 28 14:57:06 CST 2013 x86_64 x86_64 x86_64 GNU/Linux [admin@bufer108081.tbc ~]$ cat /etc/redhat-release Red Hat Enterprise Linux Server release 5.7 (Tikanga) [admin@bufer108081.tbc ~]$ java -version
java version "1.7.0_51" Java(TM) SE Runtime Environment (build 1.7.0_51-b13) OpenJDK (Alibaba) 64-Bit Server VM (build 24.45-b08-internal, mixed mode) [admin@bufer108081.tbc ~]$ ulimit -a
core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0 file size (blocks, -f) unlimited
pending signals (-i) 387068 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited
open files (-n) 131072 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited
max user processes (-u) unlimited virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited [admin@bufer108081.tbc ~/dev/baoniu]$ free -g
             total       used       free     shared    buffers     cached Mem: 47 31 15 0 3 25 -/+ buffers/cache: 3 44 Swap: 0 0 0

测试程序见本文最后面。测试结果:突破了网上所说的32000个线程数,成功创建了 10万个线程
(由于/proc/sys/kernel/pid_max默认为32768,所以网上很多测试程序测试JVM只能创建32000个线程。)

[admin@bufer108081.tbc ~/dev/baoniu]$ java -Xss128k MaxThreadsMain The stack size specified is too small, Specify at least 228k Error: Could not create the Java Virtual Machine. Error: A fatal exception has occurred. Program will exit. [admin@bufer108081.tbc ~/dev/baoniu]$ java -Xss228k MaxThreadsMain ,000 threads: Time to create 4,000 threads was 0.846 seconds ,000 threads: Time to create 4,000 threads was 2.425 seconds ,000 threads: Time to create 4,000 threads was 4.813 seconds ,000 threads: Time to create 4,000 threads was 7.229 seconds ,000 threads: Time to create 4,000 threads was 10.443 seconds ,000 threads: Time to create 4,000 threads was 14.480 seconds ,000 threads: Time to create 4,000 threads was 19.709 seconds ,000 threads: Time to create 4,000 threads was 24.742 seconds ,000 threads: Time to create 4,000 threads was 31.181 seconds ,000 threads: Time to create 4,000 threads was 36.629 seconds ,000 threads: Time to create 4,000 threads was 42.796 seconds ,000 threads: Time to create 4,000 threads was 48.659 seconds ,000 threads: Time to create 4,000 threads was 55.030 seconds ,000 threads: Time to create 4,000 threads was 60.130 seconds ,000 threads: Time to create 4,000 threads was 67.419 seconds ,000 threads: Time to create 4,000 threads was 73.507 seconds ,000 threads: Time to create 4,000 threads was 79.416 seconds ,000 threads: Time to create 4,000 threads was 85.261 seconds ,000 threads: Time to create 4,000 threads was 92.201 seconds ,000 threads: Time to create 4,000 threads was 98.087 seconds ,000 threads: Time to create 4,000 threads was 108.263 seconds ,000 threads: Time to create 4,000 threads was 114.840 seconds ,000 threads: Time to create 4,000 threads was 121.841 seconds ,000 threads: Time to create 4,000 threads was 127.714 seconds After creating 99,410 threads, java.lang.OutOfMemoryError: unable to create new native thread
        at java.lang.Thread.start0(Native Method) at java.lang.Thread.start(Thread.java:713) at MaxThreadsMain.addThread(MaxThreadsMain.java:43) at MaxThreadsMain.main(MaxThreadsMain.java:13)

创建9W多个线程后,进程占用内存:VIRT=40.5g RES=4.7g,用free -g查看系统还有9G的空闲(free)内存。


JVM最多能启动的线程数参照公式:


(MaxProcessMemory - JVMMemory  ReservedOsMemory) / (ThreadStackSize) = Number of threads
  • MaxProcessMemory : 进程的最大寻址空间
  • JVMMemory : JVM内存
  • ReservedOsMemory : 保留的操作系统内存,如Native heap,JNI之类,一般100多M
  • ThreadStackSize : 线程栈的大小,jvm启动时由Xss指定

MaxProcessMemory:如32位的linux默认每个进程最多申请3G的地址空间,64位的操作系统可以支持到46位(64TB)的物理地址空间和47位(128T)的进程虚拟地址空间(linux 64位CPU内存限制)。

JVM内存:由Heap区和Perm区组成。通过-Xms和-Xmx可以指定heap区大小,通过-XX:PermSize和-XX:MaxPermSize指定perm区的大小(默认从32MB 到64MB,和JVM版本有关)。

线程栈ThreadStackSize:

Java程序中,每个线程都有自己的Stack Space。这个Stack Space的空间是独立分配的,与-Xmx和-Xms指定的堆大小无关。Stack Space用来做方法的递归调用时压入Stack Frame。所以当递归调用太深的时候,就有可能耗尽Stack Space,爆出StackOverflow的错误。对于32位JVM,缺省值为256KB,对于64位JVM,缺省值为512KB。最大值根据平台和特定机器配置的不同而不同。如果超过最大值,那么将报告java/lang/OutOfMemoryError消息。

可见,减少Xss指定的线程栈大小能够启动更多的线程,但是线程总数也受到系统空闲内存和操作系统的限制。

总结下影响Java线程数量的因素:

  • Java虚拟机本身:-Xms,-Xmx,-Xss;
  • 系统限制:
    /proc/sys/kernel/pid_max,
    /proc/sys/kernel/thread-max,
    max_user_process(ulimit -u),
    /proc/sys/vm/max_map_count。

ps: 最后发现是这台机器上有个应用代码问题创建了过多的线程,达到系统限制,而影响了YARN和其他应用。一般来说,单机线程数过多可以考虑使用线程池或者更多的服务器。


附测试程序:

import java.util.ArrayList; import java.util.List; public class MaxThreadsMain { public static final int BATCH_SIZE = 4000; public static void main(String... args) throws InterruptedException { List<Thread> threads = new ArrayList<Thread>(); try { for (int i = 0; i <= 100 * 1000; i += BATCH_SIZE) { long start = System.currentTimeMillis(); addThread(threads, BATCH_SIZE); long end = System.currentTimeMillis(); Thread.sleep(1000); long delay = end - start; System.out.printf("%,d threads: Time to create %,d threads was %.3f seconds %n", threads.size(), BATCH_SIZE, delay / 1e3); } } catch (Throwable e) { System.err.printf("After creating %,d threads, ", threads.size()); e.printStackTrace(); } } private static void addThread(List<Thread> threads, int num) { for (int i = 0; i < num; i++) { Thread t = new Thread(new Runnable() { @Override public void run() { try {

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