Issue
Just moved from Java 11 to Java 14
The following code is now failing on a linux machine:
String linux_exe = System.getProperty("user.dir") + '/' + "fpcalc_arm32";
List<String> params = new ArrayList();
params.add(linux_exe);
params.add("-plain");
params.add("-length");
params.add(submittedSongLength);
params.add(file.getPath());
Process p = Runtime.getRuntime().exec(params.toArray(new String[1]));
with stacktrace
Cannot run program "/mnt/system/config/Apps/SongKong/songkong/fpcalc_arm32": error=0, Failed to exec spawn helper: pid: 13998, exit value: 127
java.io.IOException: Cannot run program "/mnt/system/config/Apps/SongKong/songkong/fpcalc_arm32": error=0, Failed to exec spawn helper: pid: 13998, exit value: 127
at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1128)
at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1071)
at java.base/java.lang.Runtime.exec(Runtime.java:590)
at java.base/java.lang.Runtime.exec(Runtime.java:449)
at com.jthink.songkong.analyse.acoustid.AcoustId.generateFingerprint(AcoustId.java:217)
at com.jthink.songkong.analyse.acoustid.AcoustId.createAcoustIdFingerprint(AcoustId.java:106)
What has changed in Java 14 that would cause this ?
I ran the equivalent code on Windows using java 14 and that did run okay. But I had retried with same code base on this unix machine using both Java 11 and Java 14 and can confirm that Java 11 always works and Java 14 always fails
Solution
I have found the issue, I came across these issues on the Openjdk Bugs Database
Provide a way for Runtime.exec to use posix_spawn on linux
and
Change the Process launch mechanism default on Linux to be posix_spawn
Essentially in Java 11 Linux uses vfork to start processes but by Java 13 it now uses posix_spawn.
posix_spawn actually requires a program called jspawnhelper that is located within jre/lib. In my case this exists but it does not have execute permissions, this is because I use jlink to build a jre that just has the system modules I need, but I create this on Windows (my main dev environment).
call "C:\Program Files\AdoptOpenJDK\jdk-11.0.6.10-hotspot\bin\jlink" --module-path="C:\Code\jthink\SongKong\linux_jdk\jmods" --add-modules java.desktop,java.datatransfer,java.logging,java.management,java.naming,java.net.http,java.prefs,java.scripting,java.sql,jdk.management,jdk.unsupported,jdk.scripting.nashorn --output C:\code\jthink\songkong\linuxjre
Windows doesn't understand linux execute permissions, when I deploy my application I set execute permission on the executables that are in jre/bin but didn't know there were any executables in jre/lib. Changing the permissions on jspawnhelper to execute fixes the issue.
An alternative workaround is to add the following java option:
-Djdk.lang.Process.launchMechanism=vfork
Answered By - Paul Taylor
Answer Checked By - Candace Johnson (JavaFixing Volunteer)
