Spawned java app hangs until first is killed

Question

I am spawning a new process using
<code>
Process proc = Runtime.getRuntime().exec(commandLine, // command line
                         null, // environment
                         new java.io.File(strExeDir)); // run directory
</code>
The new process is a 2nd JVM called with the following command line:
<code>
C:\jdk1.4.2_03\jre\\bin\javaw.exe -jar "my.jar"
</code>
"my.jar" contains a manifest.mf with a Main-Class and Class-Path entries. my.jar can be executed with no problems by running that command outside of my application.
The process is spawned without an Exception being thrown. The spawned process outputs some of my initial logging statements, but then hangs until the first app is killed, no matter how long I wait.
can anyone tell me why?
Thanks in advance,
Mike

Answer 1

Originally, my app was launching, logging a few lines
of code, and hanging.
Since I made the change to cmd /c start, it is now
executing properly. The second app appears when it
should and functions properly without hanging. (An
oddity is, I never see a console window with cmd /c or
cmd /k. )That's probably because you are using javaw.exe, not java.exe. Citing the documentation, "The javaw command is identical to java, except that with javaw there is no associated console window. Use javaw when you don't want a command prompt window to appear." If your app has a problem, you would apparently benefit if it had a chance to display something about itself - so try to use 'java' instead of javaw.
In the original way, I was spawning a new process and
executing javaw.exe directly. Now I am spawning a new
process to execute cmd.exe to indirectly run javaw.
I am working on an ant script to pull all the class
files from the dependenices into my jar. This way I
can eliminate the class-path parameter from the
manifest.mf. Apparently, this application has runI think to have a class path (which changes from machine to machine) in the JAR file manifest (which is not supposed to change) is a bad idea. Why don't you just launch your second JVM with the "-classpath" parameter?
successfully in the past, and it was using this
technique. I don't really like the idea of putting
other peoples' class files in my own jar, so when they
asked me to make some mods, I decided to separate
them. I created a lib subdirectory and dumped all the
jars in it, referencing them by relative paths, i.e.,
lib/log4j.jar, in the manifest. However, this has led
me to the current problem.
Does this clarify what I'm doing?
The question remains, when I execute javaw.exe in my
execute(), why would it wait for app #1 to exit before
continuing with app #2?As I said, try java instead of javaw to see if it reports anything. Also, you may try to give not a single string to your Runtime.exec() method, but an array of Strings, each containing and individual "word" from your command string. For me at least the latter method always worked.