1<!DOCTYPE html> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> 5<meta name="generator" content="hevea 2.18"> 6<link rel="stylesheet" type="text/css" href="manual.css"> 7<title>Chapter 29  The threads library</title> 8</head> 9<body> 10<a href="libstr.html"><img src="previous_motif.gif" alt="Previous"></a> 11<a href="index.html"><img src="contents_motif.gif" alt="Up"></a> 12<a href="libgraph.html"><img src="next_motif.gif" alt="Next"></a> 13<hr> 14<h1 class="chapter" id="sec535">Chapter 29  The threads library</h1> 15<p> 16<a id="c:threads"></a></p><p>The <span class="c003">threads</span> library allows concurrent programming in OCaml. 17It provides multiple threads of control (also called lightweight 18processes) that execute concurrently in the same memory space. Threads 19communicate by in-place modification of shared data structures, or by 20sending and receiving data on communication channels.</p><p>The <span class="c003">threads</span> library is implemented by time-sharing on a single 21processor. It will not take advantage of multi-processor machines. 22Using this library will therefore never make programs run 23faster. However, many programs are easier to write when structured as 24several communicating processes.</p><p>Two implementations of the <span class="c003">threads</span> library are available, depending 25on the capabilities of the operating system: 26</p><ul class="itemize"><li class="li-itemize"> 27System threads. This implementation builds on the OS-provided threads 28facilities: POSIX 1003.1c threads for Unix, and Win32 threads for 29Windows. When available, system threads support both bytecode and 30native-code programs. 31</li><li class="li-itemize">VM-level threads. This implementation performs time-sharing and 32context switching at the level of the OCaml virtual machine (bytecode 33interpreter). It is available on Unix systems, and supports only 34bytecode programs. It cannot be used with native-code programs. 35</li></ul><p> 36Programs that use system threads must be linked as follows: 37</p><pre> 38 ocamlc -thread <span class="c009">other options</span> unix.cma threads.cma <span class="c009">other files</span> 39 ocamlopt -thread <span class="c009">other options</span> unix.cmxa threads.cmxa <span class="c009">other files</span> 40</pre><p> 41Compilation units that use the <span class="c003">threads</span> library must also be compiled with 42the <span class="c003">-thread</span> option (see chapter <a href="comp.html#c%3Acamlc">8</a>).</p><p>Programs that use VM-level threads must be compiled with the <span class="c003">-vmthread</span> 43option to <span class="c003">ocamlc</span> (see chapter <a href="comp.html#c%3Acamlc">8</a>), and be linked as follows: 44</p><pre> 45 ocamlc -vmthread <span class="c009">other options</span> threads.cma <span class="c009">other files</span> 46</pre><p> 47Compilation units that use <span class="c003">threads</span> library must also be compiled with 48the <span class="c003">-vmthread</span> option (see chapter <a href="comp.html#c%3Acamlc">8</a>).</p><ul class="ftoc2"><li class="li-links"> 49<a href="libref/Thread.html">Module <span class="c003">Thread</span>: lightweight threads</a> 50</li><li class="li-links"><a href="libref/Mutex.html">Module <span class="c003">Mutex</span>: locks for mutual exclusion</a> 51</li><li class="li-links"><a href="libref/Condition.html">Module <span class="c003">Condition</span>: condition variables to synchronize between threads</a> 52</li><li class="li-links"><a href="libref/Event.html">Module <span class="c003">Event</span>: first-class synchronous communication</a> 53</li><li class="li-links"><a href="libref/ThreadUnix.html">Module <span class="c003">ThreadUnix</span>: thread-compatible system calls</a> 54</li></ul> 55<hr> 56<a href="libstr.html"><img src="previous_motif.gif" alt="Previous"></a> 57<a href="index.html"><img src="contents_motif.gif" alt="Up"></a> 58<a href="libgraph.html"><img src="next_motif.gif" alt="Next"></a> 59</body> 60</html> 61
