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| 23 | <a accesskey="p" href="../threads.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../threads.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="concepts.html"><img src="../images/next.png" alt="Next"></a> |
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| 24 | </div> |
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| 25 | <div class="section" lang="en"> |
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| 26 | <div class="titlepage"><div><div><h3 class="title"> |
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| 27 | <a name="threads.design"></a>Design</h3></div></div></div> |
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| 28 | <div class="toc"><dl> |
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| 29 | <dt><span class="section"><a href="design.html#threads.design.goals">Goals</a></span></dt> |
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| 30 | <dt><span class="section"><a href="design.html#id2775596">Iterative Phases</a></span></dt> |
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| 31 | <dt><span class="section"><a href="design.html#id2775636">Phase 1, Synchronization Primitives</a></span></dt> |
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| 32 | <dt><span class="section"><a href="design.html#threads.design.phase2">Phase 2, Thread Management and Thread Specific Storage</a></span></dt> |
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| 33 | <dt><span class="section"><a href="design.html#id2775808">The Next Phase</a></span></dt> |
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| 34 | </dl></div> |
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| 35 | <p>With client/server and three-tier architectures becoming common place |
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| 36 | in today's world, it's becoming increasingly important for programs to be |
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| 37 | able to handle parallel processing. Modern day operating systems usually |
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| 38 | provide some support for this through native thread APIs. Unfortunately, |
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| 39 | writing portable code that makes use of parallel processing in C++ is made |
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| 40 | very difficult by a lack of a standard interface for these native APIs. |
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| 41 | Further, these APIs are almost universally C APIs and fail to take |
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| 42 | advantage of C++'s strengths, or to address concepts unique to C++, such as |
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| 43 | exceptions.</p> |
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| 44 | <p>The <span class="bold"><strong>Boost.Threads</strong></span> library is an attempt to define a portable interface |
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| 45 | for writing parallel processes in C++.</p> |
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| 46 | <div class="section" lang="en"> |
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| 47 | <div class="titlepage"><div><div><h4 class="title"> |
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| 48 | <a name="threads.design.goals"></a>Goals</h4></div></div></div> |
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| 49 | <p>The <span class="bold"><strong>Boost.Threads</strong></span> library has several goals that should help to set |
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| 50 | it apart from other solutions. These goals are listed in order of precedence |
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| 51 | with full descriptions below. |
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| 52 | </p> |
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| 53 | <div class="variablelist"><dl> |
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| 54 | <dt><span class="term">Portability</span></dt> |
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| 55 | <dd><p><span class="bold"><strong>Boost.Threads</strong></span> was designed to be highly portable. The goal is |
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| 56 | for the interface to be easily implemented on any platform that |
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| 57 | supports threads, and possibly even on platforms without native thread |
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| 58 | support.</p></dd> |
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| 59 | <dt><span class="term">Safety</span></dt> |
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| 60 | <dd> |
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| 61 | <p><span class="bold"><strong>Boost.Threads</strong></span> was designed to be as safe as possible. Writing |
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| 62 | <a href="../threads.html#threads.glossary.thread-safe">thread-safe</a> |
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| 63 | code is very difficult and successful libraries must strive to |
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| 64 | insulate the programmer from dangerous constructs as much as |
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| 65 | possible. This is accomplished in several ways: |
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| 66 | </p> |
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| 67 | <div class="itemizedlist"><ul type="disc"> |
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| 68 | <li><p>C++ language features are used to make correct usage easy |
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| 69 | (if possible) and error-prone usage impossible or at least more |
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| 70 | difficult. For example, see the <a href="concepts.html#threads.concepts.Mutex" title="Mutex Concept">Mutex</a> and <a href="concepts.html#threads.concepts.Lock" title="Lock Concept">Lock</a> designs, and note |
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| 71 | how they interact.</p></li> |
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| 72 | <li><p>Certain traditional concurrent programming features are |
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| 73 | considered so error-prone that they are not provided at all. For |
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| 74 | example, see <a href="rationale.html#threads.rationale.events" title="Rationale for not providing Event Variables">the section called “Rationale for not providing <span class="emphasis"><em>Event Variables</em></span>”</a>.</p></li> |
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| 75 | <li><p>Dangerous features, or features which may be misused, are |
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| 76 | identified as such in the documentation to make users aware of |
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| 77 | potential pitfalls.</p></li> |
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| 78 | </ul></div> |
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| 79 | </dd> |
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| 80 | <dt><span class="term">Flexibility</span></dt> |
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| 81 | <dd><p><span class="bold"><strong>Boost.Threads</strong></span> was designed to be flexible. This goal is often |
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| 82 | at odds with <span class="emphasis"><em>safety</em></span>. When functionality might be |
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| 83 | compromised by the desire to keep the interface safe, <span class="bold"><strong>Boost.Threads</strong></span> |
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| 84 | has been designed to provide the functionality, but to make it's use |
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| 85 | prohibitive for general use. In other words, the interfaces have been |
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| 86 | designed such that it's usually obvious when something is unsafe, and |
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| 87 | the documentation is written to explain why.</p></dd> |
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| 88 | <dt><span class="term">Efficiency</span></dt> |
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| 89 | <dd><p><span class="bold"><strong>Boost.Threads</strong></span> was designed to be as efficient as |
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| 90 | possible. When building a library on top of another library there is |
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| 91 | always a danger that the result will be so much slower than the |
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| 92 | "native" API that programmers are inclined to ignore the higher level |
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| 93 | API. <span class="bold"><strong>Boost.Threads</strong></span> was designed to minimize the chances of this |
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| 94 | occurring. The interfaces have been crafted to allow an implementation |
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| 95 | the greatest chance of being as efficient as possible. This goal is |
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| 96 | often at odds with the goal for <span class="emphasis"><em>safety</em></span>. Every |
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| 97 | effort was made to ensure efficient implementations, but when in |
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| 98 | conflict <span class="emphasis"><em>safety</em></span> has always taken |
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| 99 | precedence.</p></dd> |
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| 100 | </dl></div> |
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| 101 | </div> |
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| 102 | <div class="section" lang="en"> |
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| 103 | <div class="titlepage"><div><div><h4 class="title"> |
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| 104 | <a name="id2775596"></a>Iterative Phases</h4></div></div></div> |
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| 105 | <p>Another goal of <span class="bold"><strong>Boost.Threads</strong></span> was to take a dynamic, iterative |
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| 106 | approach in its development. The computing industry is still exploring the |
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| 107 | concepts of parallel programming. Most thread libraries supply only simple |
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| 108 | primitive concepts for thread synchronization. These concepts are very |
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| 109 | simple, but it is very difficult to use them safely or to provide formal |
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| 110 | proofs for constructs built on top of them. There has been a lot of research |
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| 111 | into other concepts, such as in "Communicating Sequential Processes." |
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| 112 | <span class="bold"><strong>Boost.Threads</strong></span> was designed in iterative steps, with each step providing |
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| 113 | the building blocks necessary for the next step and giving the researcher |
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| 114 | the tools necessary to explore new concepts in a portable manner.</p> |
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| 115 | <p>Given the goal of following a dynamic, iterative approach |
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| 116 | <span class="bold"><strong>Boost.Threads</strong></span> shall go through several growth cycles. Each phase in its |
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| 117 | development shall be roughly documented here.</p> |
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| 118 | </div> |
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| 119 | <div class="section" lang="en"> |
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| 120 | <div class="titlepage"><div><div><h4 class="title"> |
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| 121 | <a name="id2775636"></a>Phase 1, Synchronization Primitives</h4></div></div></div> |
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| 122 | <p>Boost is all about providing high quality libraries with |
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| 123 | implementations for many platforms. Unfortunately, there's a big problem |
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| 124 | faced by developers wishing to supply such high quality libraries, namely |
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| 125 | thread-safety. The C++ standard doesn't address threads at all, but real |
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| 126 | world programs often make use of native threading support. A portable |
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| 127 | library that doesn't address the issue of thread-safety is therefore not |
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| 128 | much help to a programmer who wants to use the library in his multithreaded |
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| 129 | application. So there's a very great need for portable primitives that will |
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| 130 | allow the library developer to create <a href="../threads.html#threads.glossary.thread-safe">thread-safe</a> |
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| 131 | implementations. This need far out weighs the need for portable methods to |
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| 132 | create and manage threads.</p> |
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| 133 | <p>Because of this need, the first phase of <span class="bold"><strong>Boost.Threads</strong></span> focuses |
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| 134 | solely on providing portable primitive concepts for thread |
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| 135 | synchronization. Types provided in this phase include the |
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| 136 | <code class="computeroutput"><a href="../mutex.html" title="Class mutex">boost::mutex</a></code>, |
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| 137 | <code class="computeroutput"><a href="../try_mutex.html" title="Class try_mutex">boost::try_mutex</a></code>, |
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| 138 | <code class="computeroutput"><a href="../timed_mutex.html" title="Class timed_mutex">boost::timed_mutex</a></code>, |
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| 139 | <code class="computeroutput"><a href="../recursive_mutex.html" title="Class recursive_mutex">boost::recursive_mutex</a></code>, |
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| 140 | <code class="computeroutput"><a href="../recursive_try_mutex.html" title="Class recursive_try_mutex">boost::recursive_try_mutex</a></code>, |
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| 141 | <code class="computeroutput"><a href="../recursive_timed_mutex.html" title="Class recursive_timed_mutex">boost::recursive_timed_mutex</a></code>, and |
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| 142 | <code class="computeroutput"><a href="../lock_error.html" title="Class lock_error">boost::lock_error</a></code>. These are considered the "core" |
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| 143 | synchronization primitives, though there are others that will be added in |
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| 144 | later phases.</p> |
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| 145 | </div> |
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| 146 | <div class="section" lang="en"> |
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| 147 | <div class="titlepage"><div><div><h4 class="title"> |
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| 148 | <a name="threads.design.phase2"></a>Phase 2, Thread Management and Thread Specific Storage</h4></div></div></div> |
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| 149 | <p>This phase addresses the creation and management of threads and |
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| 150 | provides a mechanism for thread specific storage (data associated with a |
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| 151 | thread instance). Thread management is a tricky issue in C++, so this |
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| 152 | phase addresses only the basic needs of multithreaded program. Later |
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| 153 | phases are likely to add additional functionality in this area. This |
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| 154 | phase of <span class="bold"><strong>Boost.Threads</strong></span> adds the <code class="computeroutput"><a href="../thread.html" title="Class thread">boost::thread</a></code> and |
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| 155 | <code class="computeroutput"><a href="../thread_specific_ptr.html" title="Class thread_specific_ptr">boost::thread_specific_ptr</a></code> types. With these |
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| 156 | additions the <span class="bold"><strong>Boost.Threads</strong></span> library can be considered minimal but |
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| 157 | complete.</p> |
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| 158 | </div> |
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| 159 | <div class="section" lang="en"> |
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| 160 | <div class="titlepage"><div><div><h4 class="title"> |
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| 161 | <a name="id2775808"></a>The Next Phase</h4></div></div></div> |
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| 162 | <p>The next phase will address more advanced synchronization concepts, |
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| 163 | such as read/write mutexes and barriers.</p> |
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| 164 | </div> |
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| 165 | </div> |
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| 166 | <table width="100%"><tr> |
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| 167 | <td align="left"><small><p>Last revised: July 17, 2004 at 04:33:59 GMT</p></small></td> |
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| 168 | <td align="right"><small>Copyright © 2001-2003 William E. Kempf</small></td> |
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| 169 | </tr></table> |
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