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    <p><strong>Edit</strong>: Fork and exec no more, since OSX can't really <code>fork</code> right. Single thread magic:</p> <pre><code>setiopolicy_np(IOPOL_TYPE_DISK, IOPOL_SCOPE_PROCESS, IOPOL_THROTTLE); system("nice -n 20 /usr/bin/purge"); setiopolicy_np(IOPOL_TYPE_DISK, IOPOL_SCOPE_PROCESS, IOPOL_DEFAULT); </code></pre> <p>This can go anywhere, in a dispatch block if you want, or anywhere in your application. No <code>fork</code> in sight. Also, feel free to replace <code>system</code> with <code>NSTask</code> if you want to stay ObjCish.</p> <hr> <p>How about a good old <code>fork</code>n<code>exec</code>:</p> <pre><code>#include &lt;unistd.h&gt; #include &lt;sys/resource.h&gt; </code></pre> <p>And:</p> <pre><code>if(fork()) { /* Set IO priority */ setiopolicy_np(IOPOL_TYPE_DISK, IOPOL_SCOPE_PROCESS, IOPOL_THROTTLE); /*IO priority is inherited*/ execl("nice", "-n", "20", "/usr/bin/purge"); } </code></pre> <p>Let's walk through this:</p> <ul> <li><code>fork</code>: Nothing to see here</li> <li><p><code>setiopolicy_np</code>: This is the place where we set IO priority (like launchd). Here are the arguments:</p> <ul> <li><code>IOPOL_TYPE_DISK</code>: We want to limit Disk I/O. There is no other option available anyway.</li> <li><code>IOPOL_SCOPE_PROCESS</code>: Affects this whole process</li> <li><code>IOPOL_THROTTLE</code>: This is the policy itself. Accouring to the <a href="https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man3/setiopolicy_np.3.html" rel="nofollow">Apple documentation</a>, it specifies this: </li> </ul> <blockquote> <p>I/Os with THROTTLE policy are called THROTTLE I/Os. If a THROTTLE I/O request occurs within a small time window (usually a fraction of a second) of another NORMAL I/O request, the thread that issues the THROTTLE I/O is forced to sleep for a certain interval. This slows down the thread that issues the THROTTLE I/O so that NORMAL I/Os can utilize most of the disk I/O bandwidth. Furthermore, a NORMAL I/O request may bypass a previously issued THROTTLE I/O request in kernel or driver queues and be sent to the device first. In some circumstances, very large THROTTLE I/O requests will be broken into smaller requests which are then issued serially.</p> </blockquote></li> </ul> <p>I/O priority is inherited, and the <code>nice</code> part of the command sets the nice value. </p>
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    1. POHow to programmatically run a command with low IO priority and high niceness value on OS X
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    1. COSounds good, but do you know if this is allowed on the Mac App Store?
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    2. CO@houbysoft: Let me do some checking.
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    3. CO@houbysoft: It should. App Sandbox allows read-only access to `/usr/bin` (and all other command directories), and I can't find anything to indicate that it limits any systems calls beyond the ones that access the file system. Now, whether `purge` can run in the sandbox is a different issue, but that's not the question.
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