How to spawn several processes from the Windows shell and wait for them all to complete?

Question

Hi,

i want to do the following from a Windows batch script:

start proc1.exe

start proc2.exe

...

start procN.exe

<wait for all N processes to complete> <-- What do i put here?

So how do i wait for all spawned processes to complete?

TIA.

Answer 1

You could do this if you write .NET code or Win32 C/C++ code to start the processes, but there is no way to do it in a batch file. once you use start to make proc1.exe run async, there is no batch command that allows you to come back later and wait for it to complete.

But you can do this easily in one of the scripting languages designed for batch work, python, WSH, etc.

For example, heres a simple script using Windows Script Host. WSH is included in all versions of Windows since Windows 98. So this script should run anywhere.

This script starts 2 programs and waits for them both to finish. Save it as as start2.wsf. The just use it in your batch file start2.wsf "prog1.exe" "prog2.exe"

<package>
 <job id="Start 2 Procs">
  <runtime>
   <description>Start 2 programs and wait for them both to finish.
   </description>
   <unnamed
      name="program"
      helpstring="the program to run"
      many="false"
      required="2"
   />
   <example>
Example: Start2.wsf "cl -c foo.obj" "cl -c bar.obj"
   </example>
  </runtime>

  <script language="JScript">

   if (WScript.Arguments.length < 2)
   {
      WScript.Arguments.ShowUsage();
      WScript.Quit();
   }

   var proc1 = WScript.Arguments.Unnamed.Item(0);
   var proc2 = WScript.Arguments.Unnamed.Item(1);

   var Shell = WScript.CreateObject("WScript.Shell");
   var oProc1 = Shell.Exec(proc1);
   var oProc2 = Shell.Exec(proc2);

   while (oProc1.Status == 0 && oProc2.Status == 0)
   {
      WScript.Sleep(1000);
   }

  </script>
 </job>
</package>

Answer 2

This is ugly, but you could wrap each command in another batch file that runs the command and then signals that the command is complete. Your main batch file would call each of those batch files asynchronously and sit in a loop waiting for the signals.

For example:

main.bat

start cmd /c proc1.bat
start cmd /c proc2.bat
:wait
sleep 1
IF NOT EXIST proc1done GOTO wait
IF NOT EXIST proc2done GOTO wait
del proc1done
del proc2done
echo All processes are complete

proc1.bat

proc1.exe
echo Done > proc1done

The sleep command is available in Windows Server 2003 Resource Kit Tools. If you don't have that, you could use a ping on localhost just to slow down that tight loop.