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Diffstat (limited to 'labs')
| -rw-r--r-- | labs/xv6.html | 42 |
1 files changed, 31 insertions, 11 deletions
diff --git a/labs/xv6.html b/labs/xv6.html index a5df08d..fcbb234 100644 --- a/labs/xv6.html +++ b/labs/xv6.html @@ -1,6 +1,6 @@ <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 @@ -140,6 +132,32 @@ initial file system. You just ran one of them: <tt>ls</tt>. <li>Use <tt>fork</tt> to create a child. <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> @@ -161,6 +179,8 @@ initial file system. You just ran one of them: <tt>ls</tt>. </ul> <h2>Optional: modify the shell</h2> + +<p>Modify the shell to support wait. <p>Modify the shell to support lists of commands, separated by ";" |