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JVM 核心技术 —— 工具与 GC 策略

lwg04522023/5/2大约 10 分钟编程开发jvm

JVM 核心技术 —— 工具与 GC 策略

1 JDK 内置命令行工具

jps -l 查看所有 Java 进程的进程号

image-20230425232345815
image-20230425232345815

jps -mlv

加上mlv参数之后可以打印更详细的信息（JVM 启动参数）

jinfo 进程号 打印 JVM 的配置信息

PS C:\Windows\system32> jinfo 8444
Attaching to process ID 8444, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.231-b11
Java System Properties:

java.runtime.name = Java(TM) SE Runtime Environment
java.vm.version = 25.231-b11
sun.boot.library.path = C:\Program Files\Java\jre1.8.0_231\bin
java.protocol.handler.pkgs = org.springframework.boot.loader
java.vendor.url = http://java.oracle.com/
java.vm.vendor = Oracle Corporation
path.separator = ;
java.rmi.server.randomIDs = true
file.encoding.pkg = sun.io
java.vm.name = Java HotSpot(TM) 64-Bit Server VM
sun.os.patch.level =
sun.java.launcher = SUN_STANDARD
user.script =
user.country = CN
user.dir = C:\Users\beam
java.vm.specification.name = Java Virtual Machine Specification
PID = 8444
java.runtime.version = 1.8.0_231-b11
java.awt.graphicsenv = sun.awt.Win32GraphicsEnvironment
os.arch = amd64
java.endorsed.dirs = C:\Program Files\Java\jre1.8.0_231\lib\endorsed
line.separator =

java.io.tmpdir = C:\Users\beam\AppData\Local\Temp\
java.vm.specification.vendor = Oracle Corporation
user.variant =
os.name = Windows 10
sun.jnu.encoding = GBK
java.library.path = C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Program Files\Java\jdk1.8.0_231\bin;C:\Program Files\Java\jre1.8.0_231\bin;C:\Java\apache-maven-3.0.5\bin;C:\Users\beam\AppData\Local\Microsoft\WindowsApps;.
spring.beaninfo.ignore = true
java.specification.name = Java Platform API Specification
java.class.version = 52.0
sun.management.compiler = HotSpot 64-Bit Tiered Compilers
os.version = 10.0
user.home = C:\Users\beam
user.timezone = Asia/Shanghai
catalina.useNaming = false
java.awt.printerjob = sun.awt.windows.WPrinterJob
file.encoding = GBK
java.specification.version = 1.8
catalina.home = C:\Users\beam\AppData\Local\Temp\tomcat.8151514544322649683.8088
user.name = beam
java.class.path = .\gateway-server-0.0.1-SNAPSHOT.jar
java.vm.specification.version = 1.8
sun.arch.data.model = 64
sun.java.command = .\gateway-server-0.0.1-SNAPSHOT.jar
java.home = C:\Program Files\Java\jre1.8.0_231
user.language = zh
java.specification.vendor = Oracle Corporation
awt.toolkit = sun.awt.windows.WToolkit
java.vm.info = mixed mode
java.version = 1.8.0_231
java.ext.dirs = C:\Program Files\Java\jre1.8.0_231\lib\ext;C:\Windows\Sun\Java\lib\ext
sun.boot.class.path = C:\Program Files\Java\jre1.8.0_231\lib\resources.jar;C:\Program Files\Java\jre1.8.0_231\lib\rt.jar;C:\Program Files\Java\jre1.8.0_231\lib\sunrsasign.jar;C:\Program Files\Java\jre1.8.0_231\lib\jsse.jar;C:\Program Files\Java\jre1.8.0_231\lib\jce.jar;C:\Program Files\Java\jre1.8.0_231\lib\charsets.jar;C:\Program Files\Java\jre1.8.0_231\lib\jfr.jar;C:\Program Files\Java\jre1.8.0_231\classes
java.awt.headless = true
java.vendor = Oracle Corporation
sun.stderr.encoding = ms936
catalina.base = C:\Users\beam\AppData\Local\Temp\tomcat.8151514544322649683.8088
file.separator = \
java.vendor.url.bug = http://bugreport.sun.com/bugreport/
sun.io.unicode.encoding = UnicodeLittle
sun.cpu.endian = little
sun.stdout.encoding = ms936
sun.desktop = windows
sun.cpu.isalist = amd64

VM Flags:
Non-default VM flags: -XX:CICompilerCount=3 -XX:InitialHeapSize=1073741824 -XX:MaxHeapSize=1073741824 -XX:MaxNewSize=357564416 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=357564416 -XX:OldSize=716177408 -XX:-UseAdaptiveSizePolicy -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
Command line:  -Xmx1g -Xms1g -XX:-UseAdaptiveSizePolicy

jstat -gc 进程号 间隔时间(单位: 毫秒) 打印次数

​ -gcutil 显示百分比

​ -gcnew 只看young区

​ -gcold 只看old区

jmap -heap pid (JDK9 之后的 jmap 不支持 -heap 参数)

PS C:\Windows\system32> jmap -heap 8444
Attaching to process ID 8444, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.231-b11

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 40
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 1073741824 (1024.0MB)
   NewSize                  = 357564416 (341.0MB)
   MaxNewSize               = 357564416 (341.0MB)
   OldSize                  = 716177408 (683.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 268435456 (256.0MB)
   used     = 23466688 (22.37957763671875MB)
   free     = 244968768 (233.62042236328125MB)
   8.742022514343262% used
From Space:
   capacity = 44564480 (42.5MB)
   used     = 0 (0.0MB)
   free     = 44564480 (42.5MB)
   0.0% used
To Space:
   capacity = 44564480 (42.5MB)
   used     = 0 (0.0MB)
   free     = 44564480 (42.5MB)
   0.0% used
PS Old Generation
   capacity = 716177408 (683.0MB)
   used     = 18446112 (17.591583251953125MB)
   free     = 697731296 (665.4084167480469MB)
   2.5756344439170022% used

16636 interned Strings occupying 2175776 bytes.

​ -histo pid 打印堆内存中的所有对象的信息

jstack [-l] pid 打印 JVM 线程栈的信息

PS C:\Windows\system32> jstack 8444
2023-04-26 00:01:01
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.231-b11 mixed mode):

"RMI Scheduler(0)" #36 daemon prio=5 os_prio=0 tid=0x00000000203ab000 nid=0x1ec0 waiting on condition [0x000000002299e000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000eab1a440> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

"RMI TCP Accept-0" #34 daemon prio=5 os_prio=0 tid=0x00000000203ad800 nid=0x16e0 runnable [0x00000000016ee000]
   java.lang.Thread.State: RUNNABLE
        at java.net.DualStackPlainSocketImpl.accept0(Native Method)
        at java.net.DualStackPlainSocketImpl.socketAccept(Unknown Source)
        at java.net.AbstractPlainSocketImpl.accept(Unknown Source)
        at java.net.PlainSocketImpl.accept(Unknown Source)
        - locked <0x00000000eab208b8> (a java.net.SocksSocketImpl)
        at java.net.ServerSocket.implAccept(Unknown Source)
        at java.net.ServerSocket.accept(Unknown Source)
        at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

"DestroyJavaVM" #33 prio=5 os_prio=0 tid=0x00000000203aa800 nid=0x1dc4 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"http-nio-8088-AsyncTimeout" #31 daemon prio=5 os_prio=0 tid=0x00000000203a9800 nid=0x1748 waiting on condition [0x0000000023d9e000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.coyote.AbstractProtocol$AsyncTimeout.run(AbstractProtocol.java:1143)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-Acceptor-0" #30 daemon prio=5 os_prio=0 tid=0x000000001cbb0000 nid=0x1128 runnable [0x0000000023c9f000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
        at sun.nio.ch.ServerSocketChannelImpl.accept(Unknown Source)
        at sun.nio.ch.ServerSocketChannelImpl.accept(Unknown Source)
        - locked <0x00000000c0605a28> (a java.lang.Object)
        at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:455)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-ClientPoller-1" #29 daemon prio=5 os_prio=0 tid=0x000000001cbae000 nid=0x808 runnable [0x0000000023b9f000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(Unknown Source)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(Unknown Source)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(Unknown Source)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(Unknown Source)
        - locked <0x00000000c0606288> (a sun.nio.ch.Util$3)
        - locked <0x00000000c0606278> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000c0606108> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(Unknown Source)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:798)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-ClientPoller-0" #28 daemon prio=5 os_prio=0 tid=0x000000001cbab000 nid=0x143c runnable [0x0000000023a9f000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(Unknown Source)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(Unknown Source)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(Unknown Source)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(Unknown Source)
        - locked <0x00000000c0611ca0> (a sun.nio.ch.Util$3)
        - locked <0x00000000c0611c90> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000c0611b20> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(Unknown Source)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:798)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-10" #27 daemon prio=5 os_prio=0 tid=0x000000001cbab800 nid=0x1f7c waiting on condition [0x000000002399f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-9" #26 daemon prio=5 os_prio=0 tid=0x000000001cbac800 nid=0x2228 waiting on condition [0x000000002379f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-8" #25 daemon prio=5 os_prio=0 tid=0x000000001cbb1800 nid=0xa30 waiting on condition [0x000000002369e000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-7" #24 daemon prio=5 os_prio=0 tid=0x000000001cbad000 nid=0xfec waiting on condition [0x000000002359f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-6" #23 daemon prio=5 os_prio=0 tid=0x000000001cbae800 nid=0x2294 waiting on condition [0x000000002349f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-5" #22 daemon prio=5 os_prio=0 tid=0x000000001cbaf800 nid=0x19fc waiting on condition [0x000000002339e000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-4" #21 daemon prio=5 os_prio=0 tid=0x000000001cbb1000 nid=0x1a00 waiting on condition [0x000000002329f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-3" #20 daemon prio=5 os_prio=0 tid=0x0000000018d95800 nid=0x1420 waiting on condition [0x000000002319e000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-2" #19 daemon prio=5 os_prio=0 tid=0x000000001abe0800 nid=0x1944 waiting on condition [0x000000002309f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"http-nio-8088-exec-1" #18 daemon prio=5 os_prio=0 tid=0x000000001f63d800 nid=0x9b8 waiting on condition [0x0000000022f9e000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000c05ff7a8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Unknown Source)

"NioBlockingSelector.BlockPoller-1" #17 daemon prio=5 os_prio=0 tid=0x0000000019642800 nid=0x17f0 runnable [0x0000000022e9f000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(Unknown Source)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(Unknown Source)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(Unknown Source)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(Unknown Source)
        - locked <0x00000000c0601e48> (a sun.nio.ch.Util$3)
        - locked <0x00000000c0601e38> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000c0601cc8> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(Unknown Source)
        at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:298)

"container-0" #16 prio=5 os_prio=0 tid=0x000000001d0bd800 nid=0x2150 waiting on condition [0x0000000022b9f000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.catalina.core.StandardServer.await(StandardServer.java:427)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer$1.run(TomcatWebServer.java:182)

"ContainerBackgroundProcessor[StandardEngine[Tomcat]]" #15 daemon prio=5 os_prio=0 tid=0x000000001813b800 nid=0x144c waiting on condition [0x0000000022a9e000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1357)
        at java.lang.Thread.run(Unknown Source)

"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x00000000173fe800 nid=0x2070 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread2" #8 daemon prio=9 os_prio=2 tid=0x0000000017373800 nid=0x1c5c waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #7 daemon prio=9 os_prio=2 tid=0x0000000015d6c000 nid=0x16a4 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #6 daemon prio=9 os_prio=2 tid=0x0000000015d6a000 nid=0xd58 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000015d68800 nid=0x1f70 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000015d67800 nid=0x12b0 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000015cf9800 nid=0x17dc in Object.wait() [0x000000001705f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000c0049eb0> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(Unknown Source)
        - locked <0x00000000c0049eb0> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(Unknown Source)
        at java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)

"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x0000000003631000 nid=0x1a4c in Object.wait() [0x0000000016f5f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000c0056368> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Unknown Source)
        at java.lang.ref.Reference.tryHandlePending(Unknown Source)
        - locked <0x00000000c0056368> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)

"VM Thread" os_prio=2 tid=0x0000000015cd7800 nid=0x2028 runnable

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000003556800 nid=0x1d64 runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000003558000 nid=0x1044 runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000003559800 nid=0xab8 runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x000000000355c000 nid=0x1554 runnable

"VM Periodic Task Thread" os_prio=2 tid=0x000000001742d000 nid=0x1a5c waiting on condition

JNI global references: 939

"kill -3 +pid"是一种向进程发送信号的命令，其中的“+pid”是进程ID。这个命令的作用是向进程发送一个SIGQUIT信号，这个信号会让进程在退出前打印出当前的堆栈信息，以便于调试。

killl -9 pid 杀死一个进程

jcmd pid help 列出所有可用的 jcmd 命令

jcmd 3712
3712:
The following commands are available:
VM.unlock_commercial_features
JFR.configure
JFR.stop
JFR.start
JFR.dump
JFR.check
VM.native_memory
ManagementAgent.stop
ManagementAgent.start_local
ManagementAgent.start
VM.classloader_stats
GC.rotate_log
Thread.print
GC.class_stats
GC.class_histogram
GC.heap_dump
GC.finalizer_info
GC.heap_info
GC.run_finalization
GC.run
VM.uptime
VM.dynlibs
VM.flags
VM.system_properties
VM.command_line
VM.version
help

jrunscript 和 jjs： 像脚本语言一样编写 Java 代码。

2 JVM 图形化工具

jconsole

jvisualvm

JDK VisualGC —— IDEA 插件

jmc （商业软件）

3 GC

3.1 GC的背景与一般原理

引用计数

循环依赖

改进 -> 标记清除算法 （ParallelGC CMSGC）

STW（stop the world）

堆内存分代

分代假设：大部分新生对象很快无用；存活时间较长的对象，可能存活更长时间。

eden：s0: s1 = 8 : 1 : 1

可以作为GC Toots的对象

  1. 当前正在执行的方法里的局部变量和输入参数
  2. 活动线程
  3. 所有类的静态字段
  4. JNI引用

清除算法 old

复制算法（标记-复制算法）young

整理算法（标记-清楚-整理算法）old

串行（ Serial ）GC / ParNewGC

并行（ Parallel ）GC

并行/并发

--XX:+UseParallelGC

--XX:ParallelGCThreads=N 指定GC线程数，默认值为CPU核心数

java8 默认的GC算法是 ParallelGC

CMS GC （Concurrent Mark and Sweep Garbage Collector）

年轻代 并行 标记-复制算法

老年代 并发 （业务线程和GC线程并发执行）标记-清除算法

不对老年代进行整理，而是使用空列表来管理内存空间的回收

为什么要用并发呢？ 让一次暂停的时间减少

CMS默认并发线程数为cpu核心数的1/4

G1 GC (Garbage-first GC)

堆不再划分年轻代和老年代，而是划分为多个可以存放对象的小块堆区

ZGC / Shenandoah GC

脱离场景谈性能都是耍流氓

默认最大堆内存

物理机内存 > 1g :: 1/4

young区 :: 1/3

old区 :: 2/3

物理机内存 < 1g :: 1/2

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