On Wed, 19 Jan 2022 09:10:56 GMT, Xin Liu <[email protected]> wrote:
>> In early stage of initialization, HotSpot doesn't handle SIGQUIT. The
>> default signal preposition on Linux is to quit the process and generate
>> coredump.
>>
>> There are 2 applications for this signal.
>> 1. There's a handshake protocol between sun.tools.attach and HotSpot.
>> VirtualMachineImpl sends SIGQUIT(3) if the AttachListener has not been
>> initialized. It expects "Signal Dispatcher" to handle SIGQUIT and create
>> AttachListener.
>> 2. POSIX systems use SIGQUIT as SIGBREAK. After AttachListener is up,
>> HotSpot will reinterpret the signal for thread dump.
>>
>> It is possible that HotSpot is still initializing in Threads::create_vm()
>> when SIGQUIT arrives. We should change JVM_HANDLE_XXX_SIGNAL to catch
>> SIGQUIT and ignore it. It is installed os::init_2() and should cover the
>> early stage of initialization. Later on, os::initialize_jdk_signal_support()
>> still overwrites the signal handler of SIGQUIT if ReduceSignalUsage is
>> false(default).
>>
>> Testing
>>
>> Before, this patch, once initialization takes long time, jcmd may quit the
>> java process.
>>
>> $java -Xms64g -XX:+AlwaysPreTouch -Xlog:gc+heap=debug:stderr
>> -XX:ParallelGCThreads=1 &
>> [1] 9589
>> [0.028s][debug][gc,heap] Minimum heap 68719476736 Initial heap 68719476736
>> Maximum heap 68719476736
>> [0.034s][debug][gc,heap] Running G1 PreTouch with 1 workers for 16384 work
>> units pre-touching 68719476736B.
>> $jcmd 9589 VM.flags
>> 9589:
>> [1] + 9589 quit java -Xms64g -XX:+AlwaysPreTouch
>> -Xlog:gc+heap=debug:stderr
>> java.io.IOException: No such process
>> at jdk.attach/sun.tools.attach.VirtualMachineImpl.sendQuitTo(Native
>> Method)
>> at
>> jdk.attach/sun.tools.attach.VirtualMachineImpl.<init>(VirtualMachineImpl.java:100)
>> at
>> jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
>> at
>> jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
>> at jdk.jcmd/sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:113)
>> at jdk.jcmd/sun.tools.jcmd.JCmd.main(JCmd.java:97)
>>
>>
>> With this patch, neither jcmd nor kill -3 will disrupt java process 45850.
>>
>> $java -Xms64g -XX:+AlwaysPreTouch -XX:ParallelGCThreads=1
>> -Xlog:os+init=debug:stderr -version &
>> [1] 45850
>> $ kill -3 45850
>> [6.902s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>>
>>
>>
>> $jcmd 45850 VM.flags
>> 45850:
>> [19.920s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>> [25.422s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>> [26.522s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>> [27.723s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>> [29.023s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>> [30.423s][info][os,init] ignore BREAK_SIGNAL in the initialization phase.
>> com.sun.tools.attach.AttachNotSupportedException: Unable to open socket file
>> /proc/45850/root/tmp/.java_pid45850: target process 45850 doesn't respond
>> within 10500ms or HotSpot VM not loaded
>> at
>> jdk.attach/sun.tools.attach.VirtualMachineImpl.<init>(VirtualMachineImpl.java:105)
>> at
>> jdk.attach/sun.tools.attach.AttachProviderImpl.attachVirtualMachine(AttachProviderImpl.java:58)
>> at
>> jdk.attach/com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:207)
>> at jdk.jcmd/sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:113)
>> at jdk.jcmd/sun.tools.jcmd.JCmd.main(JCmd.java:97)
>> $openjdk version "19-internal" 2022-09-20
>> OpenJDK Runtime Environment (fastdebug build 19-internal+0-adhoc.xxinliu.jdk)
>> OpenJDK 64-Bit Server VM (fastdebug build 19-internal+0-adhoc.xxinliu.jdk,
>> mixed mode, sharing)
>> [1] + 45850 done java -Xms64g -XX:+AlwaysPreTouch
>> -XX:ParallelGCThreads=1 -version
>
> Xin Liu has updated the pull request incrementally with one additional commit
> since the last revision:
>
> Only install JVM_HANDLE_XXX_SIGNAL when ReduceSignalUsage is
> false(default value).
>
> This patch also adds a log message with 'os+init=info'.
src/hotspot/os/posix/signals_posix.cpp line 598:
> 596:
> 597: if (!signal_was_handled && sig == BREAK_SIGNAL) {
> 598: assert(!ReduceSignalUsage, "Should not happen with
> -Xrs/-XX:-ReduceSignalUsage");
Sorry, this is a typo. -Xrs=-XX:+ReduceSignalUsage. It should be + instead of -
before ReduceSignalUsage.
I will update in next revision.
-------------
PR: https://git.openjdk.java.net/jdk/pull/7003
