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6 messages in net.java.dev.jna.usersRE: [jna-users] Re: JNA (fork and exec)| From | Sent On | Attachments |
|---|---|---|
| Timothy Wall | Aug 27, 2007 12:59 pm | |
| Wayne Meissner | Aug 27, 2007 5:28 pm | |
| Jagadeeswaran Rajendiran | Aug 28, 2007 4:56 pm | |
| Timothy Wall | Aug 28, 2007 6:51 pm | |
| Jagadeeswaran Rajendiran | Aug 29, 2007 5:49 pm | |
| Timothy Wall | Aug 29, 2007 8:48 pm |
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| Subject: | RE: [jna-users] Re: JNA (fork and exec) | Actions... |
|---|---|---|
| From: | Jagadeeswaran Rajendiran (r.ja...@loni.ucla.edu) | |
| Date: | Aug 28, 2007 4:56:13 pm | |
| List: | net.java.dev.jna.users | |
Thanks for the prompt replies, guys.
So, here are some more results/questions:
1. I tried using execl as follows.
libcInstance.execl("/bin/cp", "cp", "source", "destination");
But, it comes back with an errno of BAD_ADDRESS
If I change it to execv, it works (with the original problem of occassionally not working)
I need to use execv anyway, coz my program is going to spawn other programs with unknown number of arguments...and execv is the most convenient and functional coz it takes an array!
2. In the code excerpt, execv never returns, which probably then means that it was never executed
3. On a related note, as suggested, I tried running my application using strace:
"strace java -jar Pipeline.jar"
And it NEVER shows JNA entering fork or execv system calls, although I (after tracing JNA source code) can see that JNA goes through Function::invoke etc, calls native code...but I am not sure why I am not able to see the fork/execv call traces through strace...any ideas?
4. Also, heres the stack dump of a successful run:
CommandThread:JNA_User_0_0_1 is the thread that forks.
The new thread (before execv) renames itself to Newly_Execed_Thread.
I forced Function::invoke (in JNA) to throw an exception at the very start
(line 154)
and at the very end (line 228) of every invocation.
HEres my interpretation of the stack dumps etc:
1. When JNA's fork method is called the child seems to return first from
Function::invoke. This
always happens on successful runs. We can see that coz after fork you
dont see the statement (I am the parent) until the child () completes
the call to execv...
2. When the child calls execv Function::invoke calls the native::invoke
method
and is done...this somehow triggers the parent thread to wake up and
return from
the fork and then continue execution...coz theres a Function::invoke (line
228)
exception being thrown by Proxy::fork and the line "I am the parent" gets
printed...
3. waitpid seems to work...
--
native library -c
CommandThread:JNA_User_0_0_1 - is forking now
CommandThread:JNA_User_0_0_1method name start - fork
CommandThread:JNA_User_0_0_1library::before sync
CommandThread:JNA_User_0_0_1library::invoke getting method
CommandThread:JNA_User_0_0_1library::invoke defined callingconvention
CommandThread:JNA_User_0_0_1NativeLibrary :: before sync :: getfunction
CommandThread:JNA_User_0_0_1NativeLibrary :: before get
CommandThread:JNA_User_0_0_1NativeLibrary :: after get
CommandThread:JNA_User_0_0_1NativeLibrary :: created new function
CommandThread:JNA_User_0_0_1NativeLibrary :: put new function
CommandThread:JNA_User_0_0_1NativeLibrary :: before return
CommandThread:JNA_User_0_0_1library::invoke nativelibrary getting function
CommandThread:JNA_User_0_0_1library::invoke putting function
CommandThread:JNA_User_0_0_1library::end of sync
CommandThread:JNA_User_0_0_1method name end - fork
before returning
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:154)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.fork(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:227)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_1 :: function :: invoke
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:228)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.fork(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:227)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_1 :: function :: before returning result
CommandThread:JNA_User_0_0_1 - execing right now
New_Execed Thread - just before exec
New_Execed Threadmethod name start - execv
New_Execed Threadlibrary::before sync
New_Execed Threadlibrary::invoke getting method
New_Execed Threadlibrary::invoke defined callingconvention
New_Execed ThreadNativeLibrary :: before sync :: getfunction
New_Execed ThreadNativeLibrary :: before get
New_Execed ThreadNativeLibrary :: after get
New_Execed ThreadNativeLibrary :: created new function
New_Execed ThreadNativeLibrary :: put new function
New_Execed ThreadNativeLibrary :: before return
New_Execed Threadlibrary::invoke nativelibrary getting function
New_Execed Threadlibrary::invoke putting function
New_Execed Threadlibrary::end of sync
New_Execed Threadmethod name end - execv
function :: concatVarArgs :: arg type - class [Ljava.lang.String;
function :: concatVarArgs :: arg is Array
function :: concatVarArgs :: arg is NOT prim Array
function :: concatVarArgs :: arg is String Array
before returning
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:154)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.execv(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:243)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
New_Execed Thread :: function :: invoke
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:228)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.fork(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:227)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_1 :: function :: before returning result
CommandThread:JNA_User_0_0_1 - I am the parent
execution.CommandThread@145b02fran command
CommandThread:JNA_User_0_0_1method name start - waitpid
CommandThread:JNA_User_0_0_1library::before sync
CommandThread:JNA_User_0_0_1library::invoke getting method
CommandThread:JNA_User_0_0_1library::invoke defined callingconvention
CommandThread:JNA_User_0_0_1NativeLibrary :: before sync :: getfunction
CommandThread:JNA_User_0_0_1NativeLibrary :: before get
CommandThread:JNA_User_0_0_1NativeLibrary :: after get
CommandThread:JNA_User_0_0_1NativeLibrary :: created new function
CommandThread:JNA_User_0_0_1NativeLibrary :: put new function
CommandThread:JNA_User_0_0_1NativeLibrary :: before return
CommandThread:JNA_User_0_0_1library::invoke nativelibrary getting function
CommandThread:JNA_User_0_0_1library::invoke putting function
CommandThread:JNA_User_0_0_1library::end of sync
CommandThread:JNA_User_0_0_1method name end - waitpid
function :: concatVarArgs :: arg type - class java.lang.Integer
function :: concatVarArgs :: arg is NOT Array
function :: concatVarArgs :: arg is NOT prim Array
function :: concatVarArgs :: arg is NOT String Array
before returning
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:154)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.waitpid(Unknown Source)
at
execution.AbstractCommandThread.waitForCompletion(AbstractCommandThread.java:402)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:555)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_1 :: function :: invoke
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:228)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.waitpid(Unknown Source)
at
execution.AbstractCommandThread.waitForCompletion(AbstractCommandThread.java:402)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:555)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_1 :: function :: before returning result
--
5. Heres the command stack from the unsuccessful run:
You will see that execv was not executed in this particular run...coz there is one Exception (line 154) and 2 Exceptions (for line 228) which means there were two threads created but the child died before it could execute ....and I am not sure why?
--
Enode - JNA_User_0has started running
JNA_User_0spawning command children
this - spawning - my child - JNA_User_00
this - spawnED - my child - JNA_User_00
JNA_User_0awaiting command child -
CommandThread:JNA_User_0_0_111 - is forking now
CommandThread:JNA_User_0_0_111method name start - fork
CommandThread:JNA_User_0_0_111library::before sync
CommandThread:JNA_User_0_0_111library::invoke getting method
CommandThread:JNA_User_0_0_111library::end of sync
CommandThread:JNA_User_0_0_111method name end - fork
before returning
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:154)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.fork(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:227)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_111 :: function :: invoke
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:228)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.fork(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:227)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_111 :: function :: before returning result
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:228)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.fork(Unknown Source)
at
execution.AbstractCommandThread.runCommand(AbstractCommandThread.java:227)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:550)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_111 :: function :: before returning result
CommandThread:JNA_User_0_0_111 - I am the parent
execution.CommandThread@c4396aran command
CommandThread:JNA_User_0_0_111method name start - waitpid
CommandThread:JNA_User_0_0_111library::before sync
CommandThread:JNA_User_0_0_111library::invoke getting method
CommandThread:JNA_User_0_0_111library::end of sync
CommandThread:JNA_User_0_0_111method name end - waitpid
function :: concatVarArgs :: arg type - class java.lang.Integer
function :: concatVarArgs :: arg is NOT Array
function :: concatVarArgs :: arg is NOT prim Array
function :: concatVarArgs :: arg is NOT String Array
before returning
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:154)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.waitpid(Unknown Source)
at
execution.AbstractCommandThread.waitForCompletion(AbstractCommandThread.java:402)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:555)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_111 :: function :: invoke
java.lang.Exception
at com.sun.jna.Function.invoke(Function.java:228)
at com.sun.jna.Library$Handler.invoke(Library.java:154)
at $Proxy0.waitpid(Unknown Source)
at
execution.AbstractCommandThread.waitForCompletion(AbstractCommandThread.java:402)
at execution.AbstractCommandThread.run(AbstractCommandThread.java:555)
at java.lang.Thread.run(Thread.java:619)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
CommandThread:JNA_User_0_0_111 :: function :: before returning result
--
-----Original Message----- From: Timothy Wall [mailto:twal...@dev.java.net] Sent: Mon 8/27/2007 6:54 PM To: Jagadeeswaran Rajendiran Subject: Fwd: [jna-users] Re: JNA (fork and exec)
Forwarded from the use...@jna.dev.java.net mailing list:
Begin forwarded message:
From: Wayne Meissner <wmei...@gmail.com> Date: August 27, 2007 8:28:27 PM EDT To: use...@jna.dev.java.net Subject: Re: [jna-users] Re: JNA (fork and exec) Reply-To: use...@jna.dev.java.net
Timothy Wall wrote:
On Aug 24, 2007, at 8:33 PM, Jagadeeswaran Rajendiran wrote:
-- Relevant Code --
//linux is the libc.INSTANCE
if((childPid = linux.fork()) == 0){ try{ System.out.println(Thread.currentThread ().getName() + " - execing right now"); Thread.currentThread().setName("New_Execed Thread"); System.out.println(Thread.currentThread ().getName() + " - just before exec"); System.out.println("return value" + linux.execv("/bin/sleep", testArray));
Try using execl instead. JNA will be treating testArray as a vararg array, which means it is translating the above into:
linux.execv("/bin/sleep", testArray[0], testArray[1], ..., null);
If you use execl(), that will actually do the right thing.
}catch(Exception e){ System.out.println("exception in abs"); e.printStackTrace(); }
You want to add: finally { System.exit(1); }
If the exec _does_ fail for some reason, or an exception gets thrown, then you want the new VM (created by fork()) to exit - otherwise you will have two VMs running with the same set of open files, shared memory, etc. That would be A Very Bad Thing.