performance problem with process fork in gcj compiled CNI

Fri Jan 27 08:10:00 GMT 2006

I'm amazed it does anything useful at all.
Once you've created a JVM, your process is multithreaded. The fork()
child only has one of those threads active, and is only allowed to call
async-signal-safe functions until it performs an exec(). (See the SUSV3
spec of fork().) You're not even close to satisfying those
requirements.
Hans
> -----Original Message-----
> From: java-owner@gcc.gnu.org [mailto:java-owner@gcc.gnu.org] 
> On Behalf Of Ricardo Temporal
> Sent: Thursday, January 26, 2006 5:11 AM
> To: java@gcc.gnu.org
> Subject: performance problem with process fork in gcj compiled CNI
>>> performance problem with process fork in gcj compiled CNI
>> Hello,
>> I have a simple C++ program with a main function that 
> fork itself's 
> process and then it starts a loop calling some processing in 
> java compiled 
> code, using CNI.
>> I intend to split processing in a machine with 2 CPUs using fork 
> technology, I'm not able to use another solution.
>> When I run the program without forking, it takes about T 
> seconds to 
> finish consuming 100% of CPU and 50% of the machine.
>> When I run the program with a fork in the beginning, it 
> takes more than 
> 2T seconds to finish with each process consuming 100% of CPU and both 
> consuming 100% of the machine.
>> What's happening ?
>> Temporal.
>> #include <iostream>
> #include <string>
> #include <sys/types.h>
> #include <unistd.h>
> #include <gcj/cni.h>
> #include <java/lang/Double.h>
> #include <java/util/ArrayList.h>
>> using namespace std;
> using namespace java::lang;
> using namespace java::util;
>> int globalVariable = 2;
>> /*
> 	Code Templates:
>> 	http://www-personal.umich.edu/~rusekd/articles/soc_prelim.html
> 	http://www.yolinux.com/TUTORIALS/ForkExecProcesses.html
> */
>> int	main(int argc, char **argv)
> {
> 	if (argc != 3)
> 	{
> 		cerr << "usage: integer bool" << endl;
> 		return 1;
> 	}
>> 	cout << "begin" << endl;
>> 	JvCreateJavaVM(NULL);
> 	JvAttachCurrentThread(NULL, NULL);
>> string sIdentifier;
> int iStackVariable = 20;
>> pid_t pID = (atol(argv[2]) ? fork() : 1);
>> if (pID == 0) // child
> {
> // Code only executed by child process
>> sIdentifier = "Child Process: ";
> globalVariable++;
> iStackVariable++;
> }
> else if (pID < 0) // failed to fork
> {
> cerr << "Failed to fork" << endl;
> exit(1);
> // Throw exception
> }
> else // parent
> {
> // Code only executed by parent process
>> sIdentifier = "Parent Process:";
> }
>> // Code executed by both parent and child.
>> cout << sIdentifier;
> cout << " Global variable: " << globalVariable;
> cout << " Stack variable: " << iStackVariable << endl;
>> 	ArrayList	*arrayList = new ArrayList;
>> 	int	loopSize = atol(argv[1]);
> 	int	maxArraySize = loopSize >> 3;
>> 	for(int	i = 0, j = 0; i < loopSize; i++, j++)
> 	{
> 		arrayList->add(new Double((jdouble)(double)i));
>> 		if (j == maxArraySize)
> 		{
> 			j = 0;
>> 			jint	size = arrayList->size();
>> 			arrayList->clear();
>> 			cout << pID << ", clear from " << 
> (int)size << " to " << 
> (int)arrayList->size() << endl;
> 		}
> 	}
>> 	JvDetachCurrentThread();
>> 	cout << "end" << endl;
>> 	return 0;
> }
>>>