os161 / man / testbin / multiexec.html
multiexec.html
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<h2 align=center>multiexec</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
<p>
multiexec - run many exec calls at once
</p>

<h3>Synopsis</h3>
<p>
<tt>/testbin/multiexec</tt> [-j <em>nprocs</em>]
				[<em>prog</em> [<em>arg</em> ...]]
</p>

<h3>Description</h3>
<p>
<tt>multiexec</tt> forks several subprocesses and then uses user-level
semaphores to cause them to all enter
<A HREF=../syscalls/execv>execv</A> at as close as possible to the
same time.
This is useful for seeing what happens if having too many argv buffers
in use at once causes the kernel to run into problems, or to test the
efficacy of measures to mitigate those problems.
</p>

<p>
The default number of subprocesses is 12.
The default program each subprocess runs is <A HREF=../bin/pwd.html>pwd</A>.
Other larger programs can be run by giving the program name and
arguments on <tt>multiexec</tt>'s command line.
</p>

<h3>Requirements</h3>
<p>
<tt>multiexec</tt> uses the following system calls:
<ul>
<li><A HREF=../syscall/getpid.html>getpid</A></li>
<li><A HREF=../syscall/open.html>open</A></li>
<li><A HREF=../syscall/read.html>read</A></li>
<li><A HREF=../syscall/write.html>write</A></li>
<li><A HREF=../syscall/close.html>close</A></li>
<li><A HREF=../syscall/remove.html>remove</A></li>
<li><A HREF=../syscall/fork.html>fork</A></li>
<li><A HREF=../syscall/execv.html>execv</A></li>
<li><A HREF=../syscall/waitpid.html>waitpid</A></li>
<li><A HREF=../syscall/_exit.html>_exit</A></li>
</ul>
</p>

<p>
<tt>multiexec</tt> should work once you have implemented the basic
system calls.
Exactly what the requirements are for handling large multiexec
invocations is up to your course staff, although probably at a minimum
your kernel shouldn't crash.
</p>

<p>
Until you implement remove, which is typically not part of the basic
system calls assignment, <tt>multiexec</tt> will not be able to clean
up after itself.
This is untidy but not a problem.
</p>

<h3>Bugs</h3>
<p>
<tt>multiexec</tt> has a compiled-in limit of 64 words in the argv
array to be passed to its subprocesses.
Also, there should be an easy way to pass a very large argv.
In the meantime, perhaps try having <tt>multiexec</tt> run
<A HREF=bigexec.html>bigexec</A>.
</p>

<h3>Restrictions</h3>
<p>
Be aware that until you do the VM assignment and replace dumbvm,
running a lot of execs will run the system out of memory very
rapidly.
</p>

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