Why cant I delete C++ pointer in JNI DLL

Question

Hi,
I'm new to JNI and pretty rusty on C++, normally I stick to 100% Java, however I had a need for some native magic. My code works well and does the job I needed however my (old) knowledge of C++ tells me that I need to clean my objects up when I'm done. However I am unable to delete a pointer and I'm pretty sure its got something to do with JNI and lots to do with my lack of indepth knowledge. Here's what my code does.
I have a Java app (J) that statically loads my DLL
"J" calls a native c++ function within the DLL called (S).
"S" creates a C++ object using the "new" operator, called (T).
"T" is a Thread which I then start ( it runs for 1minute)
"S" does not wait for "T" to finish, instead it returns immediately, passing the pointer to "T" back to "J"
"J" then starts a normal Java Thread and every 10secs calls a native function from the DLL, called (C), and passes the pointer to "T".
"C" then checks "T" to find out if it has finished, if not then it returns % complete as an "int". If "T" has finished it throws an Exception, and then attempts to delete "T" calling the following code :-
delete T;
T = 0;
printf("\ndone\n");However it crashed on "delete T", if I comment both these lines out everything completes ok.
My first thought was that "T" is already deleted, however I've checked and this is not the case, it still points to a valid "T" object. I know this because if I let my Java Thread continue to query for status long after "T" has stopped it still gets the last status message.
So my problem is, how do I delete "T"?. The system crashes if I try......interestingly enough though if I comment out the "delete T" line and leave the "T=0" line then I get an "Access Violation" error instead.
Does this mean that C++ does not own the object anymore (becase I passed it to Java). Does Java now own it and will it garbage collect it for me?
Thanks for any help
Chris.

Answer 1

Hi,
Not sure how I can pinpoint the stack corruption? Here's the JNI log produce when I use "ie=0", perhaps it would mean something to you.
# An unexpected error has been detected by HotSpot Virtual Machine:
# EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x0afd2bb7, pid=3584, tid=1680
# Java VM: Java HotSpot(TM) Client VM (1.5.0_03-b07 mixed mode)
# Problematic frame:
# C [IEConnectionJNI.dll+0x2bb7]
--------------- T H R E A D ---------------
Current thread (0x0acc3d28): JavaThread "Thread-0" [_thread_in_native, id=1680]
siginfo: ExceptionCode=0xc0000005, reading address 0x00000010
Registers:
EAX=0x0b4cfca0, EBX=0x06c77528, ECX=0x00000000, EDX=0x0b149438
ESP=0x0b4cfc34, EBP=0x0b4cfcb0, ESI=0x0b4cfc38, EDI=0x0b4cfcb0
EIP=0x0afd2bb7, EFLAGS=0x00010246
Top of Stack: (sp=0x0b4cfc34)
0x0b4cfc34: 00001388 0acc3d28 06c77520 06c77528
0x0b4cfc44: cccccccc cccccccc cccccccc cccccccc
0x0b4cfc54: cccccccc cccccccc cccccccc cccccccc
0x0b4cfc64: cccccccc cccccccc cccccccc cccccccc
0x0b4cfc74: cccccccc cccccccc cccccccc cccccccc
0x0b4cfc84: cccccccc 0b311910 cccccccc 0b311910
0x0b4cfc94: 0b311910 cccccccc cccccccc 0b13d2d8
0x0b4cfca4: cccccccc 00a86770 00000000 0b4cfce0
Instructions: (pc=0x0afd2bb7)
0x0afd2ba7: f0 e8 ca 5f 0c 00 8b f4 68 88 13 00 00 8b 4d fc
0x0afd2bb7: 8b 51 10 52 ff 15 b8 d3 14 0b 3b f4 e8 b8 a0 00
Stack: [0x0b490000,0x0b4d0000), sp=0x0b4cfc34, free space=255k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
C [IEConnectionJNI.dll+0x2bb7]
j system.IEConnectionJNI.getDownloadStatus(I)Ljava/lang/String;+0
j system.IEConnectionJNI$ProgressCheck.run()V+17
v ~StubRoutines::call_stub
V [jvm.dll+0x818b8]
V [jvm.dll+0xd431d]
V [jvm.dll+0x81789]
V [jvm.dll+0x814e6]
V [jvm.dll+0x9c06b]
V [jvm.dll+0xfe7f5]
V [jvm.dll+0xfe7c3]
C [MSVCRT.dll+0x2a3b0]
C [kernel32.dll+0xb683]
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j system.IEConnectionJNI.getDownloadStatus(I)Ljava/lang/String;+0
j system.IEConnectionJNI$ProgressCheck.run()V+17
v ~StubRoutines::call_stub
--------------- P R O C E S S ---------------
Java Threads: ( => current thread )
0x00037180 JavaThread "DestroyJavaVM" [_thread_blocked, id=3588]
=>0x0acc3d28 JavaThread "Thread-0" [_thread_in_native, id=1680]
0x00aca528 JavaThread "Monitor Ctrl-Break" daemon [_thread_in_native, id=3660]
0x00a92730 JavaThread "Low Memory Detector" daemon [_thread_blocked, id=2336]
0x00a913a8 JavaThread "CompilerThread0" daemon [_thread_blocked, id=3648]
0x00a90730 JavaThread "Signal Dispatcher" daemon [_thread_blocked, id=3644]
0x00a87c18 JavaThread "Finalizer" daemon [_thread_blocked, id=3640]
0x00a86810 JavaThread "Reference Handler" daemon [_thread_blocked, id=2144]
Other Threads:
0x00a84ea8 VMThread [id=3624]
0x00a93908 WatcherThread [id=3656]
VM state:not at safepoint (normal execution)
VM Mutex/Monitor currently owned by a thread: None
Heap
def new generation total 576K, used 378K [0x02ad0000, 0x02b70000, 0x02fb0000)
eden space 512K, 74% used [0x02ad0000, 0x02b2eb90, 0x02b50000)
from space 64K, 0% used [0x02b50000, 0x02b50000, 0x02b60000)
to space 64K, 0% used [0x02b60000, 0x02b60000, 0x02b70000)
tenured generation total 1408K, used 0K [0x02fb0000, 0x03110000, 0x06ad0000)
the space 1408K, 0% used [0x02fb0000, 0x02fb0000, 0x02fb0200, 0x03110000)
compacting perm gen total 8192K, used 1815K [0x06ad0000, 0x072d0000, 0x0aad0000)
the space 8192K, 22% used [0x06ad0000, 0x06c95e60, 0x06c96000, 0x072d0000)
No shared spaces configured.
Dynamic libraries:
0x00400000 - 0x0040c000      C:\jdk1.5.0_03\bin\java.exe
0x7c900000 - 0x7c9b0000      C:\WINDOWS\system32\ntdll.dll
0x7c800000 - 0x7c8f4000      C:\WINDOWS\system32\kernel32.dll
0x77dd0000 - 0x77e6b000      C:\WINDOWS\system32\ADVAPI32.dll
0x77e70000 - 0x77f01000      C:\WINDOWS\system32\RPCRT4.dll
0x77c10000 - 0x77c68000      C:\WINDOWS\system32\MSVCRT.dll
0x6d6b0000 - 0x6d836000      C:\jdk1.5.0_03\jre\bin\client\jvm.dll
0x77d40000 - 0x77dd0000      C:\WINDOWS\system32\USER32.dll
0x77f10000 - 0x77f57000      C:\WINDOWS\system32\GDI32.dll
0x76b40000 - 0x76b6d000      C:\WINDOWS\system32\WINMM.dll
0x76390000 - 0x763ad000      C:\WINDOWS\system32\IMM32.DLL
0x6d2f0000 - 0x6d2f8000      C:\jdk1.5.0_03\jre\bin\hpi.dll
0x76bf0000 - 0x76bfb000      C:\WINDOWS\system32\PSAPI.DLL
0x6d680000 - 0x6d68c000      C:\jdk1.5.0_03\jre\bin\verify.dll
0x6d370000 - 0x6d38d000      C:\jdk1.5.0_03\jre\bin\java.dll
0x6d6a0000 - 0x6d6af000      C:\jdk1.5.0_03\jre\bin\zip.dll
0x10000000 - 0x10007000      C:\Program Files\JetBrains\IntelliJ IDEA 6.0\bin\breakgen.dll
0x0afd0000 - 0x0b15f000      C:\projects\relatis_systray\IEConnectionJNI.dll
0x61410000 - 0x61534000      C:\WINDOWS\system32\urlmon.dll
0x774e0000 - 0x7761d000      C:\WINDOWS\system32\ole32.dll
0x77120000 - 0x771ac000      C:\WINDOWS\system32\OLEAUT32.dll
0x77f60000 - 0x77fd6000      C:\WINDOWS\system32\SHLWAPI.dll
0x5dca0000 - 0x5dce5000      C:\WINDOWS\system32\iertutil.dll
0x5d090000 - 0x5d12a000      C:\WINDOWS\system32\COMCTL32.dll
0x771b0000 - 0x7727e000      C:\WINDOWS\system32\WININET.dll
0x003f0000 - 0x003f9000      C:\WINDOWS\system32\Normaliz.dll
0x73000000 - 0x73026000      C:\WINDOWS\system32\WINSPOOL.DRV
0x763b0000 - 0x763f9000      C:\WINDOWS\system32\comdlg32.dll
0x7c9c0000 - 0x7d1d5000      C:\WINDOWS\system32\SHELL32.dll
0x773d0000 - 0x774d3000      C:\WINDOWS\WinSxS\x86_Microsoft.Windows.Common-Controls_6595b64144ccf1df_6.0.2600.2982_x-ww_ac3f9c03\comctl32.dll
0x6d530000 - 0x6d543000      C:\jdk1.5.0_03\jre\bin\net.dll
0x71ab0000 - 0x71ac7000      C:\WINDOWS\system32\WS2_32.dll
0x71aa0000 - 0x71aa8000      C:\WINDOWS\system32\WS2HELP.dll
0x77fe0000 - 0x77ff1000      C:\WINDOWS\system32\Secur32.dll
0x71a50000 - 0x71a8f000      C:\WINDOWS\system32\mswsock.dll
0x662b0000 - 0x66308000      C:\WINDOWS\system32\hnetcfg.dll
0x71a90000 - 0x71a98000      C:\WINDOWS\System32\wshtcpip.dll
0x5ad70000 - 0x5ada8000      C:\WINDOWS\system32\uxtheme.dll
0x10100000 - 0x1010e000      C:\Program Files\Logitech\SetPoint\lgscroll.dll
0x7c340000 - 0x7c396000      C:\WINDOWS\system32\MSVCR71.dll
0x7c3a0000 - 0x7c41b000      C:\WINDOWS\system32\MSVCP71.dll
0x76ee0000 - 0x76f1c000      C:\WINDOWS\system32\RASAPI32.dll
0x76e90000 - 0x76ea2000      C:\WINDOWS\system32\rasman.dll
0x5b860000 - 0x5b8b4000      C:\WINDOWS\system32\NETAPI32.dll
0x76eb0000 - 0x76edf000      C:\WINDOWS\system32\TAPI32.dll
0x76e80000 - 0x76e8e000      C:\WINDOWS\system32\rtutils.dll
0x769c0000 - 0x76a73000      C:\WINDOWS\system32\USERENV.dll
0x722b0000 - 0x722b5000      C:\WINDOWS\system32\sensapi.dll
0x76fc0000 - 0x76fc6000      C:\WINDOWS\system32\rasadhlp.dll
0x76f20000 - 0x76f47000      C:\WINDOWS\system32\DNSAPI.dll
0x76fb0000 - 0x76fb8000      C:\WINDOWS\System32\winrnr.dll
0x76f60000 - 0x76f8c000      C:\WINDOWS\system32\WLDAP32.dll
VM Arguments:
jvm_args: -Didea.launcher.port=7534 -Didea.launcher.bin.path=C:\Program Files\JetBrains\IntelliJ IDEA 6.0\bin -Dfile.encoding=windows-1252
java_command: com.intellij.rt.execution.application.AppMain system.IEConnectionJNI
Environment Variables:
CLASSPATH=.;C:\Program Files\Java\jre1.5.0_03\lib\ext\QTJava.zip
PATH=C:\oracle\product\10.2.0\db_1\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\Program Files\ATI Technologies\ATI Control Panel;C:\Program Files\SecureCRT\;C:\exim_downloaded\bin;C:\BES\bin;C:\Program Files\QuickTime\QTSystem\;C:\Program Files\Microsoft Visual Studio\Common\MSDev98\Bin;C:\Program Files\Microsoft Visual Studio\Common\Tools;C:\Program Files\Microsoft Visual Studio\VC98\bin;C:\BES\bin
USERNAME=Chris
OS=Windows_NT
PROCESSOR_IDENTIFIER=x86 Family 15 Model 3 Stepping 4, GenuineIntel
--------------- S Y S T E M ---------------
OS: Windows XP Build 2600 Service Pack 2
CPU:total 2 family 15, cmov, cx8, fxsr, mmx, sse, sse2, ht
Memory: 4k page, physical 2096340k(1206824k free), swap 4194303k(3968120k free)
vm_info: Java HotSpot(TM) Client VM (1.5.0_03-b07) for windows-x86, built on Apr 13 2005 02:07:01 by "java_re" with MS VC++ 6.0