On Mon, 15 Mar 2021 16:59:24 GMT, Jonathan Dowland <jdowl...@openjdk.org> wrote:
>> This is an adaptation of a patch originally written by Shafi Ahmad in
>> a comment on the JBS page but never submitted or merged.
>>
>> With -Xcheck:jni, the method java.net.NetworkInterface.getAll very
>> quickly breaches the default JNI local refs threshold (32). Exactly when
>> this happens depends upon the number of network interfaces (in state "UP")
>> visible to Java. On Linux, with current Trunk, 2 network interfaces is
>> sufficient to breach:
>>
>> $ ./addif.sh 0
>> 1 interfaces
>> $ sudo ip netns exec jbase $JAVA_HOME/bin/java -Xcheck:jni NITest
>> (nothing)
>> $ ./addif.sh 1
>> 2 interfaces
>> $ sudo ip netns exec jbase $JAVA_HOME/bin/java -Xcheck:jni NITest
>> WARNING: JNI local refs: 33, exceeds capacity: 32
>> at java.net.NetworkInterface.getAll(java.base/Native Method)
>> at
>> java.net.NetworkInterface.getNetworkInterfaces(java.base/NetworkInterface.java:351)
>> at NITest.main(NITest.java:3)
>>
>> This patch improves the situation:
>>
>> $ ./addif.sh 3
>> 4 interfaces
>> $ sudo ip netns exec jbase $JAVA_HOME/bin/java -Xcheck:jni NITest
>> (nothing)
>> $ ./addif.sh 4
>> 5 interfaces
>> $ sudo ip netns exec jbase $JAVA_HOME/bin/java -Xcheck:jni NITest
>> WARNING: JNI local refs: 33, exceeds capacity: 32
>> at java.net.NetworkInterface.getAll(java.base/Native Method)
>> at
>> java.net.NetworkInterface.getNetworkInterfaces(java.base/NetworkInterface.java:351)
>> at NITest.main(NITest.java:3)
>>
>>
>> Once the JNI local refs threshold is breached, the threshold is raised.
>> With the patch, it takes 10 network interfaces to breach the new
>> threshold
>>
>> $ ./addif.sh 9
>> 10 interfaces
>> $ sudo ip netns exec jbase $JAVA_HOME/bin/java -Xcheck:jni NITest
>> WARNING: JNI local refs: 33, exceeds capacity: 32
>> at java.net.NetworkInterface.getAll(java.base/Native Method)
>> at
>> java.net.NetworkInterface.getNetworkInterfaces(java.base/NetworkInterface.java:351)
>> at NITest.main(NITest.java:3)
>> WARNING: JNI local refs: 66, exceeds capacity: 65
>> at java.net.NetworkInterface.getAll(java.base/Native Method)
>> at
>> java.net.NetworkInterface.getNetworkInterfaces(java.base/NetworkInterface.java:351)
>> at NITest.main(NITest.java:3)
>>
>> Without the patch it takes 5.
>>
>> Helper scripts for testing on Linux. `setupnet.sh`:
>>
>> #!/bin/bash
>> set -euo pipefail
>>
>> namespace=${namespace:-jbase}
>> sudo ip netns add ${namespace}
>>
>> And `addif.sh`:
>>
>> #!/bin/bash
>> set -euo pipefail
>>
>> namespace=${namespace:-jbase}
>> num="$1"
>>
>> sudo ip link add name vethhost${num} type veth peer name
>> veth${namespace}${num}
>> sudo ip link set veth${namespace}${num} netns ${namespace}
>> sudo ip addr add 192.168.2.${num}/24 dev vethhost${num}
>> sudo ip netns exec ${namespace} ip addr add 192.168.2.${num}/24 dev
>> veth${namespace}${num}
>> sudo ip link set vethhost${num} up
>> sudo ip netns exec ${namespace} ip link set veth${namespace}${num} up
>>
>> count="$(sudo ip netns exec ${namespace} ip link show |grep UP | wc -l)"
>> echo "${count} interfaces"
>
> Jonathan Dowland has updated the pull request with a new target base due to a
> merge or a rebase. The pull request now contains one commit:
>
> 8187450: JNI local refs exceeds capacity warning in NetworkInterface::getAll
src/java.base/windows/native/libnet/NetworkInterface.c line 677:
> 675: (*env)->DeleteLocalRef(env, iaObj);
> 676: (*env)->DeleteLocalRef(env, ibObj);
> 677: (*env)->DeleteLocalRef(env, ia2Obj);
ia2Obj is not guaranteed to be set to a local reference, no? (if the address
family is AF_INET6)
test/jdk/java/net/NetworkInterface/Test.java line 28:
> 26: * @library /test/lib
> 27: * @run main Test -Xcheck:jni
> 28: * @run main/othervm -Djava.net.preferIPv4Stack=true Test -Xcheck:jni
You will need to put `-Xcheck:jni` before `Test` ( rather than after it ). Also
make the first at run tag othervm also, since the test will now run with a
command line argument.
-------------
PR: https://git.openjdk.java.net/jdk/pull/2963
