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sieve exercise

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Frans Kaashoek 2019-07-24 20:30:20 -04:00
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labs/xv6.html
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<html>
<head>
<title>Homework: xv6</title>
<title>Lab: xv6</title>
<link rel="stylesheet" href="homework.css" type="text/css" />
</head>
<body>
@ -115,18 +115,10 @@ initial file system. You just ran one of them: <tt>ls</tt>.
</pre>
<p>Optional: write an uptime program that prints the uptime in terms
of ticks using the <tt>uptime</tt> system call.
of ticks using the <tt>uptime</tt> system call.
<h2>pingpong</h2>
<p>In the previous exercise, if you made an error in sleep, the
program may have exited prematurely, but it didn't affect other
processes because xv6 isolates processes. Sometimes you want
processes to interact with each other. Xv6 provides two ways to do:
either through the file system (one process can create a file and
another process can read that file) or through pipes. In this
exercise you explore interprocess communication through pipes.
<p> Write a program that uses UNIX system calls to ``ping-pong'' a
byte between two processes over a pair of pipes, one for each
direction. The parent sends by writing a byte to <tt>fd[1]</tt> and
@ -141,6 +133,32 @@ initial file system. You just ran one of them: <tt>ls</tt>.
<li>Use <tt>read</tt> to read from the pipe, and <tt>write</tt> to write to the pipe.
</ul>
<h2>primes</h2>
<p>Write a concurrent version of prime sieve using pipes. This idea
is due to Doug McIlroy, inventor of Unix pipes. The picture
halfway down <a href="http://swtch.com/~rsc/thread/">the page</a>
and the text surrounding it explain how to do it.
<p>Your goal is to use <tt>pipe</tt> and <tt>fork</tt> to set up
the pipeline. The first process feeds the numbers 2 through 35
into the pipeline. For each prime number, you will arrange to
create one process that reads from its left neighbor over a pipe
and writes to its right neighbor over another pipe. Since xv6 has
limited number of file descriptors and processes, the first
process can stop at 35.
<p>Some hints:
<ul>
<li>Be careful to close file descriptors that a process doesn't
need, because otherwise your program will run xv6 out of resources
before the first process reaches 35.
<li>Once the first process reach 35, you should arrange that the
pipeline terminates cleanly (Hint: read will return an end-of-file
when the write-side of the pipe is closed).
</ul>
<h2>find</h2>
<p>Write a simple version of the UNIX find program: find all the files
@ -162,6 +180,8 @@ initial file system. You just ran one of them: <tt>ls</tt>.
<h2>Optional: modify the shell</h2>
<p>Modify the shell to support wait.
<p>Modify the shell to support lists of commands, separated by ";"
<p>Modify the shell to support sub-shells by implementing "(" and ")"