forking a new process - High Level Programming

themezzaman · #1 (**permalink**) 06-18-2006

Hi
I'm currently working with C on UNIX (HPUX) and need to be able to fork a seperate Java process from within a running C process.
I can run the following code from the command line via a script but am having difficulty getting it to work from within the code.
I am trying to use execl. Is execl the correct command to be using?
Any help would be appreciated.
Thanks.

$JAVAHOME/jre/bin/java -cp \

/opt/mv36/em/SMD/data/jct_005/SMD_LCT.jar:/opt/mv36/em/SMD/data/jct_005/jh.jar:/nms/JamToolsTest/jct/MV36CoreProxyNOP.1.1.jar
\
com.marcx.lct.sma11d.sma11d_lct_applet \
-mv36 1 -host 19.3.11.13 -port 20020 \
-inifile /opt/mv36/em/SMD/data/jct_005/ -lang 1 -laf 0 \
-msgset 5 -emaccess 3 -command 221

blowtorch · #2 (**permalink**) 06-18-2006

Well, you can use execl, but in that case, you cannot use the $JAVAHOME env variable. You need to get the value from the env using something like getenv() and create the complete path.

The fork-exec part of the code can look like this (assuming that the path to the java command is /usr/jre/bin):

Code:

pid=fork();
if(pid==-1) {
   perror("error in fork!");
}
if(!pid) { /*child process - execute the java command*/
   execl("/usr/jre/bin/java","java","-cp","/opt/mv36/em/SMD/data/jct_005/SMD_LCT.jar:/opt/mv36/em/SMD/data/jct_005/jh.jar:/nms/JamToolsTest/jct/MV36CoreProxyNOP.1.1.jar","com.marcx.lct.sma11d.sma11d_lct_applet","-mv36","1","-host","19.3.11.13","-port","20020","-inifile","/opt/mv36/em/SMD/data/jct_005/","-lang","1","-laf","0","-msgset","5","-emaccess","3","-command","221",(char*)0)
}
else { /*in parent process - wait for child to exit*/
   wait();
}

themezzaman · #3 (**permalink**) 06-19-2006

Cheers.
Though could you tell me whether the current environment should be passed to the process run by the execl?
The execl is succesfull but the underlying java program doesn't start which is I think because it doesn't receive the DISPLAY variable from the calling code. Is there a way to set this for the child process?

Thanks.

blowtorch · #4 (**permalink**) 06-19-2006

Check the man page for fork(2).

Quote:

Originally Posted by man page of fork

The child process inherits the following attributes from the parent
process:

+ Real, effective, and saved user IDs.
+ Real, effective, and saved group IDs.
+ List of supplementary group IDs (see getgroups(2)).
+ Process group ID.
+ Environment.
+ File descriptors.
+ Close-on-exec flags (see exec(2)).
+ Signal handling settings (SIG_DFL, SIG_IGN, address).
+ Signal mask (see sigvector(2)).
+ Profiling on/off status (see profil(2)).
+ Command name in the accounting record (see acct(4)).
+ Nice value (see nice(2)).
+ All attached shared memory segments (see shmop(2)).
+ Current working directory
+ Root directory (see chroot(2)).
+ File mode creation mask (see umask(2)).
+ File size limit (see ulimit(2)).
+ Real-time priority (see rtprio(2)).

It says that the environment does get passed from parent to child. Are you sure that the DISPLAY variable is set in the parent process? Again use getenv to verify that the parent process does indeed have the DISPLAY variable set. If getenv returns NULL, DISPLAY is not set.

Cheers

themezzaman · #5 (**permalink**) 06-20-2006

Thanks for all the help Blowtorch.

More UNIX and Linux Forum Topics You Might Find Helpful
Thread	Thread Starter	Forum	Replies	Last Post
Forking with Tclsh vs Wish	pghamami	Shell Programming and Scripting	3	05-06-2008 12:33 PM
Testing the forking process.	Vitamin254	UNIX for Dummies Questions & Answers	0	02-22-2008 07:12 PM
VERY confused about forking of child process	JamesByars	UNIX for Advanced & Expert Users	7	02-22-2008 12:31 PM
forking process.	kymthasneem	High Level Programming	2	06-23-2007 10:00 AM
Forking	manjuWicky	UNIX for Advanced & Expert Users	3	10-07-2005 12:01 PM

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode