OpenEuphoria

2. Re: Two instances

• Posted by fizzpopsoft Dec 20, 2012
• 1123 views

Hi Don, The simple way would be to open a explicitly named file, and hold it open.
The second program, when attempting the same would get a -1 return from the open()

Regards,
Alan

4. Re: Two instances

• Posted by ghaberek (admin) Dec 24, 2012
• 1094 views

Don,

PID files are probably the most universal way to ensure a single instance of your application. Here is a good StackOverflow post on the topic: Reference for proper handling of PID file on Unix. On Windows, you could use the TEMP path (e.g. getenv("TEMP")) in place of /var/run. If you are using Win32Lib, a call to setAppName() will fail if an application with that name is already running.

Here is a quick example for using PID files.

include "std/error.e" 
include "std/filesys.e" 
include "std/io.e" 
 
-- get the proper path for storing pid files 
ifdef WINDOWS then 
constant TEMP = getenv( "TEMP" ) 
elsedef 
constant TEMP = "/var/run" -- you could also use /tmp or maybe ~/.var/run 
end ifdef 
 
-- build the path to our pid file 
sequence pid_path = join_path({ TEMP, "myapp.pid" }) 
 
-- open the pid file 
integer pid_file = open( pid_path, "w" ) 
if pid_file = -1 then 
    crash( "Unable to create PID file!" ) 
end if 
 
-- lock the pid file 
if not lock_file( pid_file, LOCK_EXCLUSIVE ) then 
    close( pid_file ) 
    crash( "Unable to lock PID file!" ) 
end if 
 
-- write this instance id (actual pid on Linux) 
atom this_pid = instance() 
printf( pid_file, "%d\n", {this_pid} ) 
 
-- flush and unlock the file 
flush( pid_file ) 
unlock_file( pid_file ) 
 
-- do a bunch of stuff here before exiting 
 
-- close and delete the pid file 
close( pid_file ) 
delete_file( pid_path ) 

-Greg