Java Segmentation Fault in ping-pong-mpi-tcp

[Janekdererste]

Background information

This is related to #10158 . I am opening a separate issue hoping to provide a better example of the error I am seeing.

What version of Open MPI are you using? (e.g., v3.0.5, v4.0.2, git branch name and hash, etc.)

4.1.2

Describe how Open MPI was installed (e.g., from a source/distribution tarball, from a git clone, from an operating system distribution package, etc.)

source

Please describe the system on which you are running

• Operating system/version: AlmaLinux release 8.5 (Arctic Sphynx)
• Computer hardware: Intel(R) Xeon(R) CPU E5-2630 v2 @ 2.60GHz, 12 cores, 125G
• Network type: Infiniband

---

Details of the problem

As recomendet by the Howard from the mailing list, I tried to rung ping-pong-mpi-tcp project. When I run the program in a similar fashion to mpi.sh in the repository. I receive a segmentation fault. This error happens in StringBuilder.append(String). The error report of the jvm is attached here: hs_err_pid31983.log. The log of the application looks like the following:

2022-04-05 16:50:33 [main] MPIMain.main()
INFO: Args received: [2, false]
2022-04-05 16:50:33 [main] MPIMain.main()
INFO: Args received: [2, false]
[INFO] 16:50:34:294 config.GlobalConfig.initMPI(): Thread support level: 0
[INFO] 16:50:34:294 config.GlobalConfig.initMPI(): Thread support level: 0
[INFO] 16:50:34:298 config.GlobalConfig.init(): Init [MPI_CONNECTION, isSingleJVM:false]
[INFO] 16:50:34:298 config.GlobalConfig.init(): Init [MPI_CONNECTION, isSingleJVM:false]
[INFO] 16:50:35:494 config.GlobalConfig.registerRole(): Registering role: Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=false}
[INFO] 16:50:35:503 config.GlobalConfig.registerRole(): Registering role: Role{roleId='p1g2', myAddress=MPIAddress{rank=1, groupId=2}, isLeader=false}
[INFO] 16:50:35:540 config.GlobalConfig.registerAddress(): Address [MPIAddress{rank=0, groupId=2}] registered on role [Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=true}]
[INFO] 16:50:35:540 config.GlobalConfig.registerAddress(): Address [MPIAddress{rank=1, groupId=2}] registered on role [Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=true}]
[INFO] 16:50:35:541 role.Node.<init>(): Node created: Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=true}
[INFO] 16:50:35:541 config.GlobalConfig.registerAddress(): Address [MPIAddress{rank=1, groupId=2}] registered on role [Role{roleId='p1g2', myAddress=MPIAddress{rank=1, groupId=2}, isLeader=true}]
[INFO] 16:50:35:541 config.GlobalConfig.registerAddress(): Address [MPIAddress{rank=0, groupId=2}] registered on role [Role{roleId='p1g2', myAddress=MPIAddress{rank=1, groupId=2}, isLeader=false}]
[INFO] 16:50:35:542 role.Node.<init>(): Node created: Role{roleId='p1g2', myAddress=MPIAddress{rank=1, groupId=2}, isLeader=false}
[node500:31983:0:31990] Caught signal 11 (Segmentation fault: address not mapped to object at address 0x14)
[INFO] 16:50:36:566 testframework.TestFramework._doPingTests(): Starting ping-pong tests...
==== backtrace (tid:  31990) ====
 0  /usr/lib64/libucs.so.0(ucs_handle_error+0x2a4) [0x1512416f32a4]
 1  /usr/lib64/libucs.so.0(+0x2347c) [0x1512416f347c]
 2  /usr/lib64/libucs.so.0(+0x2364a) [0x1512416f364a]
 3  [0x1512949256d4]
=================================
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00001512949256d4 (sent by kill), pid=31983, tid=31990
#
# JRE version: OpenJDK Runtime Environment (17.0.2+8) (build 17.0.2+8-86)
# Java VM: OpenJDK 64-Bit Server VM (17.0.2+8-86, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, serial gc, linux-amd64)
# Problematic frame:
# J 448 c2 java.lang.StringBuilder.append(Ljava/lang/String;)Ljava/lang/StringBuilder; java.base@17.0.2 (8 bytes) @ 0x00001512949256d4 [0x00001512949256a0+0x0000000000000034]
#
# Core dump will be written. Default location: Core dumps may be processed with "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %e" (or dumping to /net/ils/laudan/2-mpi-test/core.31983)
#
# An error report file with more information is saved as:
# /net/ils/laudan/2-mpi-test/hs_err_pid31983.log
Compiled method (c2)    3781  448       4       java.lang.StringBuilder::append (8 bytes)
 total in heap  [0x0000151294925510,0x0000151294925fb0] = 2720
 relocation     [0x0000151294925670,0x00001512949256a0] = 48
 main code      [0x00001512949256a0,0x0000151294925be0] = 1344
 stub code      [0x0000151294925be0,0x0000151294925bf8] = 24
 metadata       [0x0000151294925bf8,0x0000151294925c50] = 88
 scopes data    [0x0000151294925c50,0x0000151294925e88] = 568
 scopes pcs     [0x0000151294925e88,0x0000151294925f68] = 224
 dependencies   [0x0000151294925f68,0x0000151294925f70] = 8
 handler table  [0x0000151294925f70,0x0000151294925f88] = 24
 nul chk table  [0x0000151294925f88,0x0000151294925fb0] = 40
[node500:31983] *** Process received signal ***
[node500:31983] Signal: Aborted (6)
[node500:31983] Signal code:  (-6)
#
# If you would like to submit a bug report, please visit:
#   https://bugreport.java.com/bugreport/crash.jsp
#
[node500:31983] [ 0] /usr/lib64/libpthread.so.0(+0x12c20)[0x1512aa492c20]
[node500:31983] [ 1] /usr/lib64/libc.so.6(gsignal+0x10f)[0x1512a9eee37f]
[node500:31983] [ 2] /usr/lib64/libc.so.6(abort+0x127)[0x1512a9ed8db5]
[node500:31983] [ 3] /net/homes/ils/laudan/jdk-17.0.2/lib/server/libjvm.so(+0x246cc9)[0x1512a8e90cc9]
[node500:31983] [ 4] /net/homes/ils/laudan/jdk-17.0.2/lib/server/libjvm.so(+0xe0e70c)[0x1512a9a5870c]
[node500:31983] [ 5] /net/homes/ils/laudan/jdk-17.0.2/lib/server/libjvm.so(+0xe0f12b)[0x1512a9a5912b]
[node500:31983] [ 6] /net/homes/ils/laudan/jdk-17.0.2/lib/server/libjvm.so(+0xe0f15e)[0x1512a9a5915e]
[node500:31983] [ 7] /net/homes/ils/laudan/jdk-17.0.2/lib/server/libjvm.so(JVM_handle_linux_signal+0x198)[0x1512a9906148]
[node500:31983] [ 8] /usr/lib64/libpthread.so.0(+0x12c20)[0x1512aa492c20]
[node500:31983] [ 9] [0x1512949256d4]
[node500:31983] *** End of error message ***
--------------------------------------------------------------------------
Primary job  terminated normally, but 1 process returned
a non-zero exit code. Per user-direction, the job has been aborted.
--------------------------------------------------------------------------
--------------------------------------------------------------------------
mpirun noticed that process rank 0 with PID 0 on node node500 exited on signal 6 (Aborted).
--------------------------------------------------------------------------

The program was started with the following command:

OMPI="/homes2/ils/laudan/ompi-java17/bin/mpirun"
JAVA="/homes2/ils/laudan/jdk-17.0.2/bin/java"
$OMPI --mca pml ucx -np 2\
 $JAVA -cp ping-pong-mpi-tcp-1.0-SNAPSHOT-jar-with-dependencies.jar MPIMain 2 false

Any help would be much appreciated.

[jsquyres]

Forgive me; I'm fairly ignorant of Java. I tried to replicate the problem, but I notice that when I run the mpi.sh from the https://github.com/mboysan/ping-pong-mpi-tcp project, the maven build downloads an Open MPI jarfile for v4.0.1. I assume it then uses that jarfile to run the application.

How do I get it to use my local Open MPI Java install?

[Janekdererste]

Thank you very much for trying it out. This is a little tedious, unfortunately.

The jar has to be in some kind of maven repository. You could create a local maven repository like this:

$ mvn deploy:deploy-file \
-Durl=file:///path/to/where/you/want/the/local/maven/repo/to/be \
-Dfile=/path/to/your/mpi.jar \
-DgroupId=org.openmpi \
-DartifactId=mpi \
-Dpackaging=jar \
-Dversion=4.1.2

ArtifactId, groupId and version can be chosen how ever you like

Then in the pom.xml, the local repository needs to be added to the <repositories> section. Like this:

<repository>
    <id>Local-mpi</id>
    <url>file:///path/to/where/you/want/the/local/maven/repo/to/be</url>
</repository>

Then in the <dependecies> section of the pom.xml file you can replace the mpi dependency with the following:

<dependency>
        <groupId>org.openmpi</groupId>
        <artifactId>mpi</artifactId>
        <version>4.1.2</version>
</dependency>

GroupId, artifactId and version must match what you have specified in the mvn:deploy command.

[jsquyres]

Thanks! Let me give this a whirl.

[jsquyres]

@Janekdererste Thanks for the instructions -- with that, I got the ping pong to compile and run with my local Open MPI Java build.

Unfortunately, it runs successfully for me. However, I see that you're using UCX. I wonder if there's some kind of conflict here with registered memory for InfiniBand...?

@open-mpi/ucx Can you please have a look at this? NOTE: While the same issue undoubtedly exists in main/v5.0.x, be aware of #10245 in terms of installing PMIx/PRTE in the same prefix as OMPI (at least until the issue is resolved).

[yosefe]

@Janekdererste can you please try without ucx (replace "--mca pml ucx" by "-mca btl tcp")?
@jsquyres how do the Java OpenMPI bindings work in the sense of making sure the buffer virtual address is not moved before a non-blocking MPI request is completed?

[jsquyres]

@yosefe IIRC, the Java bindings use some sort of special type of Java buffer that is effectively pinned.

[ggouaillardet]

@Janekdererste in order to force btl/tcp you will need to

mpirun --mca pml ob1 --mca btl tcp,self

[jsquyres]

@yosefe Check out https://docs.open-mpi.org/en/v5.0.x/features/java.html#how-to-specify-buffers. These are the upcoming 5.0 docs, but the content basically hasn't changed since Open MPI v4.x.

[jsquyres]

@Janekdererste While researching this issue, I also updated the Java Open MPI docs. I came across this statement in the docs:

All non-blocking methods must use direct buffers and only blocking methods can choose between arrays and direct buffers.

Does your app (and/or this sample ping-pong app) use any non-blocking MPI methods? If so, are direct buffers used?

[Janekdererste]

Thanks all for helping on this issue. I tried to run the program with
mpirun --mca pml ob1 --mca btl tcp,self -np 2 java -cp ./target/*jar-with-dependencies.jar MPIMain 2 false
as suggested by @ggouaillardet. The program seems to crash in the same place. The jvm dumps (hs_err_pid22088.log
hs_err_pid22089.log) of the two processes
and the log looks like this:

2022-04-11 14:48:58 [main] MPIMain.main()
INFO: Args received: [2, false]
2022-04-11 14:48:58 [main] MPIMain.main()
INFO: Args received: [2, false]
[INFO] 14:48:59:484 config.GlobalConfig.initMPI(): Thread support level: 0
[INFO] 14:48:59:484 config.GlobalConfig.initMPI(): Thread support level: 0
[INFO] 14:48:59:490 config.GlobalConfig.init(): Init [MPI_CONNECTION, isSingleJVM:false]
[INFO] 14:48:59:490 config.GlobalConfig.init(): Init [MPI_CONNECTION, isSingleJVM:false]
[node301:22089:0:22090] Caught signal 11 (Segmentation fault: invalid permissions for mapped object at address 0x149ea6032008)
==== backtrace (tid:  22090) ====
 0  /usr/lib64/libucs.so.0(ucs_handle_error+0x2a4) [0x149e3a28b2a4]
 1  /usr/lib64/libucs.so.0(+0x2347c) [0x149e3a28b47c]
 2  /usr/lib64/libucs.so.0(+0x2364a) [0x149e3a28b64a]
 3  [0x149e852414e0]
=================================
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x0000149e852414e0, pid=22089, tid=22090
#
# JRE version: Java(TM) SE Runtime Environment (11.0.2+9) (build 11.0.2+9-LTS)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (11.0.2+9-LTS, mixed mode, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# J 292 c1 java.util.Objects.requireNonNull(Ljava/lang/Object;Ljava/lang/String;)Ljava/lang/Object; java.base@11.0.2 (15 bytes) @ 0x0000149e852414e0 [0x0000149e85241460+0x0000000000000080]
#
# Core dump will be written. Default location: Core dumps may be processed with "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %e" (or dumping to /net/ils/laudan/2-mpi-test/ping-pong-mpi-tcp/core.22089)
#
# An error report file with more information is saved as:
# /net/ils/laudan/2-mpi-test/ping-pong-mpi-tcp/hs_err_pid22089.log
Compiled method (c1)    1140  292       3       java.util.Objects::requireNonNull (15 bytes)
 total in heap  [0x0000149e85241290,0x0000149e85241748] = 1208
 relocation     [0x0000149e85241408,0x0000149e85241448] = 64
 main code      [0x0000149e85241460,0x0000149e85241600] = 416
 stub code      [0x0000149e85241600,0x0000149e852416a8] = 168
 metadata       [0x0000149e852416a8,0x0000149e852416b0] = 8
 scopes data    [0x0000149e852416b0,0x0000149e852416e0] = 48
 scopes pcs     [0x0000149e852416e0,0x0000149e85241740] = 96
 dependencies   [0x0000149e85241740,0x0000149e85241748] = 8
Could not load hsdis-amd64.so; library not loadable; PrintAssembly is disabled
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
#
[node301:22089] *** Process received signal ***
[node301:22089] Signal: Aborted (6)
[node301:22089] Signal code:  (-6)
[node301:22089] [ 0] /usr/lib64/libpthread.so.0(+0x12c20)[0x149ea5aebc20]
[node301:22089] [ 1] /usr/lib64/libc.so.6(gsignal+0x10f)[0x149ea533637f]
[node301:22089] [ 2] /usr/lib64/libc.so.6(abort+0x127)[0x149ea5320db5]
[node301:22089] [ 3] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xc00be9)[0x149ea4a72be9]
[node301:22089] [ 4] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29619)[0x149ea4c9b619]
[node301:22089] [ 5] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29e9b)[0x149ea4c9be9b]
[node301:22089] [ 6] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29ece)[0x149ea4c9bece]
[node301:22089] [ 7] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe2aedd)[0x149ea4c9cedd]
[node301:22089] [ 8] /usr/lib64/libpthread.so.0(+0x12c20)[0x149ea5aebc20]
[node301:22089] [ 9] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0x75f834)[0x149ea45d1834]
[node301:22089] [10] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0x75ee65)[0x149ea45d0e65]
[node301:22089] [11] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe25376)[0x149ea4c97376]
[node301:22089] [12] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe27b22)[0x149ea4c99b22]
[node301:22089] [13] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe293b7)[0x149ea4c9b3b7]
[node301:22089] [14] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29e9b)[0x149ea4c9be9b]
[node301:22089] [15] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29ece)[0x149ea4c9bece]
[node301:22089] [16] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(JVM_handle_linux_signal+0x1c0)[0x149ea4a7da00]
[node301:22089] [17] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xbff5e8)[0x149ea4a715e8]
[node301:22089] [18] /usr/lib64/libpthread.so.0(+0x12c20)[0x149ea5aebc20]
[node301:22089] [19] [0x149e852414e0]
[node301:22089] *** End of error message ***
[INFO] 14:48:59:769 config.GlobalConfig.registerRole(): Registering role: Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=false}
[INFO] 14:48:59:783 config.GlobalConfig.registerAddress(): Address [MPIAddress{rank=0, groupId=2}] registered on role [Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=true}]
[INFO] 14:48:59:784 config.GlobalConfig.registerAddress(): Address [MPIAddress{rank=1, groupId=2}] registered on role [Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=true}]
[INFO] 14:48:59:784 role.Node.<init>(): Node created: Role{roleId='p0g2', myAddress=MPIAddress{rank=0, groupId=2}, isLeader=true}
[INFO] 14:49:00:790 testframework.TestFramework._doPingTests(): Starting ping-pong tests...
[node301:22088:0:22091] Caught signal 11 (Segmentation fault: address not mapped to object at address 0xc)
==== backtrace (tid:  22091) ====
 0  /usr/lib64/libucs.so.0(ucs_handle_error+0x2a4) [0x149785e4d2a4]
 1  /usr/lib64/libucs.so.0(+0x2347c) [0x149785e4d47c]
 2  /usr/lib64/libucs.so.0(+0x2364a) [0x149785e4d64a]
 3  [0x1497d8725ef4]
=================================
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00001497d8725ef4, pid=22088, tid=22091
#
# JRE version: Java(TM) SE Runtime Environment (11.0.2+9) (build 11.0.2+9-LTS)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (11.0.2+9-LTS, mixed mode, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# J 440 c2 java.lang.StringBuilder.append(Ljava/lang/String;)Ljava/lang/StringBuilder; java.base@11.0.2 (8 bytes) @ 0x00001497d8725ef4 [0x00001497d8725ec0+0x0000000000000034]
#
# Core dump will be written. Default location: Core dumps may be processed with "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %e" (or dumping to /net/ils/laudan/2-mpi-test/ping-pong-mpi-tcp/core.22088)
#
# An error report file with more information is saved as:
# /net/ils/laudan/2-mpi-test/ping-pong-mpi-tcp/hs_err_pid22088.log
Compiled method (c2)    2222  440       4       java.lang.StringBuilder::append (8 bytes)
 total in heap  [0x00001497d8725d10,0x00001497d87267d8] = 2760
 relocation     [0x00001497d8725e88,0x00001497d8725eb8] = 48
 main code      [0x00001497d8725ec0,0x00001497d87264a0] = 1504
 stub code      [0x00001497d87264a0,0x00001497d87264b8] = 24
 metadata       [0x00001497d87264b8,0x00001497d8726500] = 72
 scopes data    [0x00001497d8726500,0x00001497d87266a8] = 424
 scopes pcs     [0x00001497d87266a8,0x00001497d8726788] = 224
 dependencies   [0x00001497d8726788,0x00001497d8726790] = 8
 handler table  [0x00001497d8726790,0x00001497d87267a8] = 24
 nul chk table  [0x00001497d87267a8,0x00001497d87267d8] = 48
Could not load hsdis-amd64.so; library not loadable; PrintAssembly is disabled
[node301:22088] *** Process received signal ***
[node301:22088] Signal: Aborted (6)
[node301:22088] Signal code:  (-6)
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
#
[node301:22088] [ 0] /usr/lib64/libpthread.so.0(+0x12c20)[0x1497f1729c20]
[node301:22088] [ 1] /usr/lib64/libc.so.6(gsignal+0x10f)[0x1497f0f7437f]
[node301:22088] [ 2] /usr/lib64/libc.so.6(abort+0x127)[0x1497f0f5edb5]
[node301:22088] [ 3] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xc00be9)[0x1497f06b0be9]
[node301:22088] [ 4] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29619)[0x1497f08d9619]
[node301:22088] [ 5] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29e9b)[0x1497f08d9e9b]
[node301:22088] [ 6] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xe29ece)[0x1497f08d9ece]
[node301:22088] [ 7] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(JVM_handle_linux_signal+0x1c0)[0x1497f06bba00]
[node301:22088] [ 8] /afs/math.tu-berlin.de/software/java/jdk-11.0.2/lib/server/libjvm.so(+0xbff5e8)[0x1497f06af5e8]
[node301:22088] [ 9] /usr/lib64/libpthread.so.0(+0x12c20)[0x1497f1729c20]
[node301:22088] [10] [0x1497d8725ef4]
[node301:22088] *** End of error message ***
--------------------------------------------------------------------------
Primary job  terminated normally, but 1 process returned
a non-zero exit code. Per user-direction, the job has been aborted.
--------------------------------------------------------------------------
--------------------------------------------------------------------------
mpirun noticed that process rank 1 with PID 0 on node node301 exited on signal 6 (Aborted).
--------------------------------------------------------------------------

[Janekdererste]

I hope this information helps:

@jsquyres said:

I see that you're using UCX.

I also tried to run this on a cluster with an Omnipath network. This yields the same errors.

@jsquyres said:

run with my local Open MPI Java

When I try to run the example with my local installation (WSL - Ubuntu 20.04) everything works fine.

Also, I tried to call the ompi-c-api directly via Java's Foreign Function & Memory Api. (This api is still in incubator state, but I though I'd give it a try - it is something similar to jni, but calls c-binaries directly without intermediate binding code as with jni)

While experimenting with this api I ran into the same errors as with the official ompi-java-binding. This let me to speculate that the issue doesn't lie within the ompi-java-bindings, but maybe OpenMPI and the JVM somehow run into a conflict.

[Janekdererste]

Does your app (and/or this sample ping-pong app) use any non-blocking MPI methods? If so, are direct buffers used?

The Ping-Pong example uses iSend and iRecv in two places. Both seem to be using direct buffers as suggested by the documentation.

The example from #10158 for example has no send or receive at all, but also crashes on a string operation as well. Due to this behaviour I would think that this might not be related to sending messages or maybe not even related to the Ompi-Java-Binding.