You might want to look at this link for a more detailed explanation on what happens when you mix threads and fork (which is always the case when calling fork from java since the jvm has it own threads) http://unix.derkeiler.com/Newsgroups/comp.unix.programmer/2003-09/0672.html. -Daniel

On 1/8/09, *rzo* <rz...@gmx.de <mailto:rz...@gmx.de>> wrote:

Hello,

I finaly solved this by calling the start() method not from within the main thread but from a new thread. Thus fork() is not called from the main thread.

- Ron

Timothy Wall wrote:

<div class="moz-text-flowed" style="font-family: -moz-fixed">Take a look at some of the recent discussion of forking a VM. When you do a successful fork, do you get a clone of the entire VM or only the forking thread?

https://jna.dev.java.net/servlets/SearchList?list=users&searchText=fork&defaultField=body&Search=Search <https://jna.dev.java.net/servlets/SearchList?list=users&searchText=fork&defaultField=body&Search=Search>

On Jan 7, 2009, at 1:21 PM, rzo wrote:

Hello,

attached is a test program. When I run it as is, everything is fine. However whenever I change code parts, even if they are not required, such as remove unused methods (for example pipe()) in the interface CLibrary, or if I call System.getProperties().list(System.out) The program fails (the fork starts a process which crashes).

Any help or hints are welcome.

The program has been tested with : Mac Os X 10.5.5, JDK 1.5.0_16, 32 bit.

- Ron package test.mac;

import java.util.concurrent.Executor; import java.util.concurrent.Executors; import java.util.logging.ConsoleHandler; import java.util.logging.Logger;

import org.rzo.yajsw.os.posix.UnixProcess.CLibrary; import org.rzo.yajsw.os.posix.UnixProcess.CLibrary.dirent64;

import com.sun.jna.Library; import com.sun.jna.Native; import com.sun.jna.Pointer; import com.sun.jna.Structure; import com.sun.jna.ptr.IntByReference;

public class ForkTest { protected static final Executor executor = Executors.newCachedThreadPool(); int pid; Logger _appLogger;

public interface CLibrary extends Library {

CLibrary INSTANCE = (CLibrary) Native.loadLibrary((System.getProperty("os.name <http://os.name/>").startsWith("Windows") ? "msvcrt" : "c"), CLibrary.class);

int fork();

void exit(int status);

/* * int execv (const charfilename, charconst argv[]) */ int execvp(String filename, String[] argv);

/* * int pipe (int filedes[2]) */ int pipe(int filedes[]);

/* * int close(int fd) */ int close(Pointer fd);

int close(int fd);

/* * mode_t umask (mode_t mask) */ void umask(int mask);

int setsid();

/* * FILE freopen ( const char filename, const char mode, FILE stream ); */ Pointer freopen(String filename, String mode, int stream);

/* * int kill (pid_t pid, int signum) */ int kill(int pid, int signum);

static final int SIGTERM = 15; static final int SIGKILL = 9;

/* * pid_t waitpid(pid_t pid, intstat_loc, int options); */ int waitpid(int pid, IntByReference stat_loc, int options);

static final int ESRCH = 3;

/* * int chdir(const charpath); */ int chdir(String path);

static final int WNOHANG = 1; /* don't hang in wait */ static final int WUNTRACED = 2; /* * tell about stopped, untraced * children */

/* * int fputc (int c, FILEstream) */ int fputc(int c, Pointer stream);

/* * FILEfdopen(int fildes, const chartype); */ Pointer fdopen(Pointer fildes, String type);

/* * int fileno(FILEstream); */ int fileno(int stream);

/* * struct dirent64 { __u64 d_ino; __s64 d_off; unsigned short d_reclen; * unsigned char d_type; char d_name[256]; }; */ class dirent64 extends Structure { public long d_ino; public long d_off; public short d_reclen; public char d_type; public char[] d_name = new char[256];

public String getName() { return getPointer().getString(8 + 8 + 2 + 1, false); } };

/* * struct dirent { long d_ino; off_t d_off; unsigned short d_reclen; * char d_name[NAME_MAX+1]; }; */ class dirent extends Structure { public int d_ino; public int d_off; public short d_reclen; public String d_name; };

/* * DIR opendir (const chardirname) */ Pointer opendir(String dirname);

/* * struct dirent64 readdir64 (DIRdirstream) */ dirent64 readdir64(Pointer dirstream);

/* * int closedir (DIRdirstream) */ int closedir(Pointer dirstream);

/* * int nice (int increment) */ int nice(int increment);

/* * int sched_setaffinity (pid_t pid, size_t cpusetsize, const cpu_set_t * cpuset) */ int sched_setaffinity(int pid, int cpusetsize, IntByReference cpuset);

/* * pid_t getpid(void); */ int getpid(); /* * int symlink (const char *oldname, const char *newname) */ int symlink (String oldname, String newname); /* * struct passwd

The passwd data structure is used to hold information about entries in the system user data base. It has at least the following members:

char *pw_name The user's login name. char *pw_passwd. The encrypted password string. uid_t pw_uid The user ID number. gid_t pw_gid The user's default group ID number. char *pw_gecos A string typically containing the user's real name, and possibly other information such as a phone number. char *pw_dir The user's home directory, or initial working directory. This might be a null pointer, in which case the interpretation is system-dependent. char *pw_shell The user's default shell, or the initial program run when the user logs in. This might be a null pointer, indicating that the system default should be used. */ public static class passwd extends Structure { public passwd(Pointer p) { super(); if (p != null) { this.useMemory(p); this.read(); } } public String pw_name; public String pw_passwd; public int pw_uid; public int pw_gid; public String pw_gecos; public String pw_dir; public String pw_shell; String getName() { return pw_name; } int getUid() { return pw_uid; } } /* * struct passwd * getpwnam (const char *name) * This function returns a pointer to a statically-allocated structure containing information about the user whose user name is name. This structure may be overwritten on subsequent calls to getpwnam.

A null pointer return indicates there is no user named name. */ Pointer getpwnam (String name); /* * uid_t geteuid (void)

The geteuid function returns the effective user ID of the process. */ int geteuid (); /* * struct passwd * getpwuid (uid_t uid)

This function returns a pointer to a statically-allocated structure containing information about the user whose user ID is uid. This structure may be overwritten on subsequent calls to getpwuid.

A null pointer value indicates there is no user in the data base with user ID uid. */ Pointer getpwuid (int uid); /* * int setreuid (uid_t ruid, uid_t euid) */ int setreuid (int ruid, int euid); /* * int chmod (const char *filename, mode_t mode) */ int chmod (String filename, int mode);

}

public boolean start() {

final IntByReference status = new IntByReference(); if ((pid = CLibrary.INSTANCE.fork()) == 0) { try { String[] cmd = new String[]{"ping", "localhost"}; int i = CLibrary.INSTANCE.execvp(cmd[0], cmd); //System.out.println("forked"); //System.exit(0); } catch (Exception ex) { ex.printStackTrace(); } //System.exit(0); // CLibrary.INSTANCE.exit(-1); } // child code else if (pid > 0) { System.out.println("started process " + pid); executor.execute(new Runnable() {

public void run() { System.out.println("waiting"); int r = CLibrary.INSTANCE.waitpid(pid, status, 0); if (r == pid) setExitCode(status.getValue()); } });

return true; } // parent process else if (pid < 0) { System.out.println("failed to fork: " + pid); return false; } return false;

} void kill() { CLibrary.INSTANCE.kill(pid, 9); } void setExitCode(int code) { System.out.println("exit code "+code); } public static void main(String[] args) { ForkTest t = new ForkTest(); //System.getProperties().list(System.out); t.start(); try { Thread.sleep(5000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } t.kill(); }

}

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