Mercurial > urweb
comparison demo/prose @ 697:755a71c99be5
Threads demo
| author | Adam Chlipala <adamc@hcoop.net> |
|---|---|
| date | Sun, 05 Apr 2009 10:48:11 -0400 |
| parents | bab524996fca |
| children | 9b29ce0babb8 |
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| 696:79a49c509007 | 697:755a71c99be5 |
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| 232 </ol> | 232 </ol> |
| 233 | 233 |
| 234 <p><tt>BatchFun.Make</tt> handles the plumbing of allocating the local state, using it to create widgets, and reading the state values when the user clicks "Batch it."</p> | 234 <p><tt>BatchFun.Make</tt> handles the plumbing of allocating the local state, using it to create widgets, and reading the state values when the user clicks "Batch it."</p> |
| 235 | 235 |
| 236 <p><tt>batchG.ur</tt> contains an example instantiation, which is just as easy to write as in the <tt>Crud1</tt> example.</p> | 236 <p><tt>batchG.ur</tt> contains an example instantiation, which is just as easy to write as in the <tt>Crud1</tt> example.</p> |
| 237 | |
| 238 threads.urp | |
| 239 | |
| 240 <p>Ur/Web makes it easy to write multi-threaded client-side code. This example demonstrates two threads writing to a page at once.</p> | |
| 241 | |
| 242 <p>First, we define a useful component for sections of pages that can have lines of text added to them dynamically. This is the <tt>Buffer</tt> module. It contains an abstract type of writable regions, along with functions to create a region, retrieve a signal representing its HTML rendering, and add a new line to it.</p> | |
| 243 | |
| 244 <p>The entry point to the main module <tt>Threads</tt> begins by creating a buffer. The function <tt>loop</tt> implements writing to that buffer periodically, incrementing a counter each time. The arguments to <tt>loop</tt> specify a prefix for the messages and the number of milliseconds to wait between writes.</p> | |
| 245 | |
| 246 <p>We specify some client-side code to run on page load using the <tt>onload</tt> attribute of <tt><body></tt>. The <tt>onload</tt> code in this example spawns two separate threads running the <tt>loop</tt> code with different prefixes, update intervals, and starting counters.</p> | |
| 247 | |
| 248 <p>Old hands at concurrent programming may be worried at the lack of synchronization in this program. Ur/Web uses <i>cooperative multi-threading</i>, not the more common <i>preemptive</i> multi-threading. Only one thread runs at a time, and only particular function calls can trigger context switches. In this example, <tt>sleep</tt> is the only such function that appears.</p> |