RFR: 8187450: JNI local refs exceeds capacity warning in NetworkInterface::getAll [v3]

[Jonathan Dowland]

> 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

-------------

Changes: https://git.openjdk.java.net/jdk/pull/2963/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2963&range=02
  Stats: 21 lines in 3 files changed: 19 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2963.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2963/head:pull/2963

PR: https://git.openjdk.java.net/jdk/pull/2963