A working version of jmap -F
Try running jmap without the -F option again. You can also increase the time that it will wait to connect, by specifying the option -J-Dsun.tools.attach.attachTimeout=<milliseconds> with a longer timeout. The default is only 5 seconds, and sometimes it takes longer than that for the VM to respond.
The current version of jmap -F (or jmap -dump:format=b,file=dump.hprof /path/to/java corefile) doesn't handle lambdas correctly, and generates a corrupted heap dump file. If you try to load it with jhat, you get errors like this:
WARNING: Class 1825e75d8 not found, adding fake class!
WARNING: Failed to resolve object id 0x1803c30a0 for field clazz (signature L)
The Eclipse MAT utterly rejects these corrupt heap dump files, and several bugs have been filed, such as https://bugs.eclipse.org/bugs/show_bug.cgi?id=471757. The error would typically look like this:
!ENTRY org.eclipse.osgi 4 0 2016-05-20 18:37:11.795
!MESSAGE Application error
!STACK 1
java.lang.NullPointerException
at org.eclipse.mat.hprof.HprofParserHandlerImpl.resolveClassHierarchy(HprofParserHandlerImpl.java:587)
at org.eclipse.mat.hprof.Pass2Parser.readInstanceDump(Pass2Parser.java:205)
at org.eclipse.mat.hprof.Pass2Parser.readDumpSegments(Pass2Parser.java:159)
at org.eclipse.mat.hprof.Pass2Parser.read(Pass2Parser.java:89)
You can download the current version from the releases page.
First you need a core file. You can get that using:
gcore <pid>
You may need sudo depending on your ptrace_scope settings.
To turn a core file into a heap dump:
java -cp heap_dump.jar:/usr/lib/jvm/java-8-oracle/lib/sa-jdi.jar \
com.addepar.heapdump.HeapDumper -f <output.hprof> /usr/bin/java <corefile>
Like jmap, jstack and the other Serviceability Agent tools, you must run this against the same version of java that was used to generate the core file.
This is a two-day hack. It has not been extensively tested.
I copied most of the code directly out of the JDK, and it retains the original GPLv2 license from there. Neither I nor Oracle is responsible for any damage it causes. See the LICENSE file for details.