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Full Discussion: Multiple jobs reading from same file
Top Forums Shell Programming and Scripting Multiple jobs reading from same file Post 302413134 by erichpowell on Wednesday 14th of April 2010 04:44:18 PM
Old 04-14-2010
Thanks, Franklin52, that's precisely what I had in mind, but what I was actually getting at was the safety of this technique.

I know that multiple processes writing to the same file is a recipe for trouble, understandably, but I was curious whether multiple jobs/processes reading from the same file is also dangerous.

For example, what happens if they both try to read the same block of memory at the same time?

My googling turned up some forum topics about this in C code, where it did seem to be an issue, but I was going to submit jobs to the background like in Franklin52's post. Can I rely on the OS to sort out any conflicts between the processes?
 

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pvm

PVM(1PVM)							  PVM Version 3.4							 PVM(1PVM)

NAME

       pvm - PVM version 3 console

SYNOPSIS

       pvm [ -options ] [ hostfile ]

DESCRIPTION

       Pvm  is a stand alone PVM task which allows the user to interactively query and modify the virtual machine.  The console can be started and
       stopped multiple times on any of the hosts in the virtual machine without affecting PVM or any applications that may be running.

       When started pvm determines if PVM is already running and if not automatically executes pvmd3 on this host, passing pvmd3 the command  line
       options and host file.  Thus PVM need not be running to start the console.  Once started the console prints the prompt:
	    pvm>

       The following console commands are available:
	   add	hostname(s)    - Add hosts to virtual machine
	   alias	       - Define/list command aliases
	   conf 	       - List virtual machine configuration
	   delete  hostname(s) - Delete hosts from virtual machine
	   echo 	       - Echo arguments
	   export	       - Add environment variables to spawn export list
	   halt 	       - Stop pvmds
	   help [command]      - Print helpful information about a command
	   id		       - Print console task id
	   jobs 	       - List running jobs
	   kill  task-tid      - Terminate tasks
	   mstat host-tid      - Show status of hosts
	   ps -a	       - List all PVM tasks
	   pstat task-tid      - Show status of tasks
	   quit 	       - Exit console
	   reset	       - Kill all tasks
	   setenv	       - Display/set environment variables
	   sig	signum task    - Send signal to task
	   spawn [opt] a.out   - Spawn task
		opts are: -(count)  number of tasks, default is 1
		    -(host)   spawn on host, default is any
		    -(ARCH)   spawn on hosts of ARCH
		    -?	      enable debugging
			  ->	    redirect task output to console
			  -> file   redirect task output to file
			  ->>file   redirect task output append to file
	   trace	       - Set/display trace event mask
	   unexport - Remove environment variables from spawn export list
	   unalias - Undefine command alias
	   version - Show libpvm version

       pvm reads $HOME/.pvmrc before reading commands from the tty, so it can be used to customize the console environment, for example:
	   alias ? help
	   alias j jobs
	   setenv PVM_EXPORT DISPLAY
	   # print my id
	   echo new pvm shell
	   id

EXAMPLES

	    pvm
       Starts up pvmd3 on the local host or connects to running pvmd3.

	    pvm  hostfile
       Starts up console and pvmd3, which inturn reads the host file and adds the listed computers to the virtual machine.

SEE ALSO

       pvm_intro(1PVM), pvmd3(1PVM)

								  30 August, 1993							 PVM(1PVM)
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