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class="sidebar-sub-headers"></ul></li><li><section class="sidebar-group"><button class="sidebar-heading clickable active"><span class="title">二、Java核心</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.1 Java概述</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.2 Java语法基础</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.3 数组&字符串</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.4 面向对象编程</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span 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class="sidebar-heading clickable active"><span class="title">2.11 并发编程</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><a href="/thread/wangzhe-thread.html" class="nav-link sidebar-link sidebar-page" aria-label="创建Java线程的3种方式">创建Java线程的3种方式</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/thread-state-and-method.html" class="nav-link sidebar-link sidebar-page" aria-label="线程的6种状态及切换">线程的6种状态及切换</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/thread-group-and-thread-priority.html" class="nav-link sidebar-link sidebar-page" aria-label="线程组和线程优先级">线程组和线程优先级</a><ul class="sidebar-sub-headers"></ul></li><li><a aria-current="page" href="/thread/why-need-thread.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="进程与线程的区别">进程与线程的区别</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a aria-current="page" href="/thread/why-need-thread.html#进程的产生" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="进程的产生">进程的产生</a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/thread/why-need-thread.html#线程的提出" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="线程的提出">线程的提出</a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/thread/why-need-thread.html#线程带来的好处" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="线程带来的好处">线程带来的好处</a><ul class="sidebar-sub-headers"></ul></li></ul></li><li><a href="/thread/thread-bring-some-problem.html" class="nav-link sidebar-link sidebar-page" aria-label="并发编程带来了哪些问题">并发编程带来了哪些问题</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/jmm.html" class="nav-link sidebar-link sidebar-page" aria-label="Java内存模型">Java内存模型</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/volatile.html" class="nav-link sidebar-link sidebar-page" aria-label="volatile">volatile</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/synchronized.html" class="nav-link sidebar-link sidebar-page" aria-label="synchronized">synchronized</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/cas.html" class="nav-link sidebar-link sidebar-page" aria-label="CAS的原理">CAS的原理</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/aqs.html" class="nav-link sidebar-link sidebar-page" aria-label="AQS详解">AQS详解</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/lock.html" class="nav-link sidebar-link sidebar-page" aria-label="锁">锁</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/reentrantLock.html" class="nav-link sidebar-link sidebar-page" aria-label="重入锁ReentrantLock">重入锁ReentrantLock</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/ReentrantReadWriteLock.html" class="nav-link sidebar-link sidebar-page" aria-label="读写锁ReentrantReadWriteLock">读写锁ReentrantReadWriteLock</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/condition.html" class="nav-link sidebar-link sidebar-page" aria-label="线程协作类Condition">线程协作类Condition</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/LockSupport.html" class="nav-link sidebar-link sidebar-page" aria-label="线程阻塞唤醒类LockSupport">线程阻塞唤醒类LockSupport</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/map.html" class="nav-link sidebar-link sidebar-page" aria-label="并发集合容器">并发集合容器</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/ConcurrentHashMap.html" class="nav-link sidebar-link sidebar-page" aria-label="ConcurrentHashMap">ConcurrentHashMap</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/ConcurrentLinkedQueue.html" class="nav-link sidebar-link sidebar-page" aria-label="ConcurrentLinkedQueue">ConcurrentLinkedQueue</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/CopyOnWriteArrayList.html" class="nav-link sidebar-link sidebar-page" aria-label="CopyOnWriteArrayList">CopyOnWriteArrayList</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/ThreadLocal.html" class="nav-link sidebar-link sidebar-page" aria-label="ThreadLocal">ThreadLocal</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/BlockingQueue.html" class="nav-link sidebar-link sidebar-page" aria-label="BlockingQueue">BlockingQueue</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/pool.html" class="nav-link sidebar-link sidebar-page" aria-label="线程池">线程池</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/ScheduledThreadPoolExecutor.html" class="nav-link sidebar-link sidebar-page" aria-label="计划任务">计划任务</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/atomic.html" class="nav-link sidebar-link sidebar-page" aria-label="原子操作类">原子操作类</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/CountDownLatch.html" class="nav-link sidebar-link sidebar-page" aria-label="通信工具类CountDownLatch">通信工具类CountDownLatch</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/fork-join.html" class="nav-link sidebar-link sidebar-page" aria-label="Fork/Join框架">Fork/Join框架</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/thread/shengchanzhe-xiaofeizhe.html" class="nav-link sidebar-link sidebar-page" aria-label="生产者-消费者模式">生产者-消费者模式</a><ul class="sidebar-sub-headers"></ul></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.12 JVM</span><span class="arrow right"></span></button></section></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">三、Java企业级开发</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">四、数据库</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">五、计算机基础</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">六、求职面试</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">七、学习资源</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">八、学习建议</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">九、知识库搭建</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">十、联系作者</span><span class="arrow right"></span></button></section></li></ul></aside><main class="page" id="main-content"><nav class="breadcrumb disable"></nav><div class="page-title"><h1>进程与线程的区别是什么？</h1><div class="page-info"><span class="author-info" aria-label="作者🖊" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon author-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="author icon"><path d="M649.6 633.6c86.4-48 147.2-144 147.2-249.6 0-160-128-288-288-288s-288 128-288 288c0 108.8 57.6 201.6 147.2 249.6-121.6 48-214.4 153.6-240 288-3.2 9.6 0 19.2 6.4 25.6 3.2 9.6 12.8 12.8 22.4 12.8h704c9.6 0 19.2-3.2 25.6-12.8 6.4-6.4 9.6-16 6.4-25.6-25.6-134.4-121.6-240-243.2-288z"></path></svg><span><a class="author-item" href="/about-the-author/" target="_blank" rel="noopener noreferrer">沉默王二</a></span><span property="author" content="沉默王二"></span></span><span class="date-info" 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33.473z"></path></svg><span>2022年3月23日</span><meta property="datePublished" content="2022-03-23T12:08:58.000Z"></span><span class="category-info" aria-label="分类🌈" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon category-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="category icon"><path d="M148.41 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H148.41c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.311-40.31zM147.556 553.478H429.73c22.263 0 40.311 18.048 40.311 40.31v282.176c0 22.263-18.048 40.312-40.31 40.312H147.555c-22.263 0-40.311-18.049-40.311-40.312V593.79c0-22.263 18.048-40.311 40.31-40.311zM593.927 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H593.927c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.31-40.31zM730.22 920.502H623.926c-40.925 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11.651-7.638 19.03v5.825h566.49v-5.825c0-7.379-2.849-13.981-7.509-18.9-5.049-193.016-97.867-351.985-220.2-389.527 123.24-37.67 216.446-198.453 220.588-392.892zM531.16 450.445v352.632c117.674 1.553 211.787 40.778 211.787 88.676H304.097c0-48.286 95.149-87.382 213.728-88.676V450.445c-93.077-3.107-167.901-81.297-167.901-177.093 0-8.803 6.99-15.793 15.793-15.793 8.803 0 15.794 6.99 15.794 15.793 0 80.261 63.69 145.635 142.01 145.635s142.011-65.374 142.011-145.635c0-8.803 6.99-15.793 15.794-15.793s15.793 6.99 15.793 15.793c0 95.019-73.789 172.82-165.96 177.093z"></path></svg><span>大约 9 分钟</span><meta property="timeRequired" content="PT9M"></span></div><hr></div><div class="toc-place-holder"><aside id="toc"><div class="toc-header">此页内容</div><div class="toc-wrapper"><ul class="toc-list"><li class="toc-item"><a aria-current="page" href="/thread/why-need-thread.html#进程的产生" class="router-link-active router-link-exact-active toc-link level2">进程的产生</a></li><li class="toc-item"><a aria-current="page" href="/thread/why-need-thread.html#线程的提出" class="router-link-active router-link-exact-active toc-link level2">线程的提出</a></li><li class="toc-item"><a aria-current="page" href="/thread/why-need-thread.html#线程带来的好处" class="router-link-active router-link-exact-active toc-link level2">线程带来的好处</a></li></ul></div></aside></div><div class="theme-hope-content"><h1 id="进程与线程的区别是什么" tabindex="-1"><a class="header-anchor" href="#进程与线程的区别是什么" aria-hidden="true">#</a> 进程与线程的区别是什么？</h1><h2 id="进程的产生" tabindex="-1"><a class="header-anchor" href="#进程的产生" aria-hidden="true">#</a> 进程的产生</h2><p>最初的计算机只能接受一些特定的指令，用户每输入一个指令，计算机就做出一个操作。当用户在思考或者输入时，计算机就在等待。这样效率非常低下，在很多时候，计算机都处在等待状态。</p><p><strong>批处理操作系统</strong></p><p>后来有了<strong>批处理操作系统</strong>,把一系列需要操作的指令写下来，形成一个清单，一次性交给计算机。用户将多个需要执行的程序写在磁带上，然后交由计算机去读取并逐个执行这些程序，并将输出结果写在另一个磁带上。</p><p>批处理操作系统在一定程度上提高了计算机的效率，但是由于<strong>批处理操作系统的指令运行方式仍然是串行的，内存中始终只有一个程序在运行</strong>，后面的程序需要等待前面的程序执行完成后才能开始执行，而前面的程序有时会由于I/O操作、网络等原因阻塞，所以<strong>批处理操作效率也不高</strong>。</p><p><strong>进程的提出</strong></p><p>人们对于计算机的性能要求越来越高，现有的批处理操作系统并不能满足人们的需求，而批处理操作系统的瓶颈在于内存中只存在一个程序，那么内存中能不能存在多个程序呢？这是人们亟待解决的问题。</p><p>于是，科学家们提出了进程的概念。</p><p>进程就是<strong>应用程序在内存中分配的空间，也就是正在运行的程序</strong>，各个进程之间互不干扰。同时进程保存着程序每一个时刻运行的状态。</p><blockquote><p>程序：用某种编程语言(java、python等)编写，能够完成一定任务或者功能的代码集合,是指令和数据的有序集合，是<strong>一段静态代码</strong>。</p></blockquote><p>此时，CPU采用时间片轮转的方式运行进程：CPU为每个进程分配一个时间段，称作它的时间片。如果在时间片结束时进程还在运行，则暂停这个进程的运行，并且CPU分配给另一个进程（这个过程叫做上下文切换）。如果进程在时间片结束前阻塞或结束，则CPU立即进行切换，不用等待时间片用完。</p><blockquote><p>当进程暂停时，它会保存当前进程的状态（进程标识，进程使用的资源等），在下一次切换回来时根据之前保存的状态进行恢复，接着继续执行。</p></blockquote><p>使用进程+CPU时间片轮转方式的操作系统，在宏观上看起来同一时间段执行多个任务，换句话说，<strong>进程让操作系统的并发成为了可能</strong>。虽然并发从宏观上看有多个任务在执行，但在事实上，对于<strong>单核CPU</strong>来说，任意具体时刻都只有一个任务在占用CPU资源。</p><p><strong>对操作系统的要求进一步提高</strong></p><p>虽然进程的出现，使得操作系统的性能大大提升，但是随着时间的推移，人们并不满足一个进程在一段时间只能做一件事情，如果一个进程有多个子任务时，只能逐个得执行这些子任务，很影响效率。</p><blockquote><p>比如杀毒软件在检测用户电脑时，如果在某一项检测中卡住了，那么后面的检测项也会受到影响。或者说当你使用杀毒软件中的扫描病毒功能时，在扫描病毒结束之前，无法使用杀毒软件中清理垃圾的功能，这显然无法满足人们的要求。</p></blockquote><h2 id="线程的提出" tabindex="-1"><a class="header-anchor" href="#线程的提出" aria-hidden="true">#</a> 线程的提出</h2><p>那么能不能让这些子任务同时执行呢？于是人们又提出了线程的概念，<strong>让一个线程执行一个子任务，这样一个进程就包含了多个线程，每个线程负责一个单独的子任务。</strong></p><blockquote><p>使用线程之后，事情就变得简单多了。当用户使用扫描病毒功能时，就让扫描病毒这个线程去执行。同时，如果用户又使用清理垃圾功能，那么可以先暂停扫描病毒线程，先响应用户的清理垃圾的操作，让清理垃圾这个线程去执行。响应完后再切换回来，接着执行扫描病毒线程。</p><p>注意：操作系统是如何分配时间片给每一个线程的，涉及到线程的调度策略，有兴趣的同学可以看一下《操作系统》，本文不做深入详解。</p></blockquote><p>总之，进程和线程的提出极大的提高了操作系统的性能。<strong>进程让操作系统的并发性成为了可能，而线程让进程的内部并发成为了可能。</strong></p><p><strong>多进程的方式也可以实现并发，为什么我们要使用多线程？</strong></p><p>多进程方式确实可以实现并发，但使用多线程，有以下几个好处：</p><ul><li>进程间的通信比较复杂，而线程间的通信比较简单，通常情况下，我们需要使用共享资源，这些资源在线程间的通信比较容易。</li><li>进程是重量级的，而线程是轻量级的，故多线程方式的系统开销更小。</li></ul><p><strong>进程和线程的区别</strong></p><p>进程是一个独立的运行环境，而线程是在进程中执行的一个任务。他们两个本质的区别是<strong>是否单独占有内存地址空间及其它系统资源（比如I/O）</strong>：</p><ul><li><p>进程单独占有一定的内存地址空间，所以进程间存在内存隔离，数据是分开的，数据共享复杂但是同步简单，各个进程之间互不干扰；而线程共享所属进程占有的内存地址空间和资源，数据共享简单，但是同步复杂。</p></li><li><p>进程单独占有一定的内存地址空间，一个进程出现问题不会影响其他进程，不影响主程序的稳定性，可靠性高；一个线程崩溃可能影响整个程序的稳定性，可靠性较低。</p></li><li><p>进程单独占有一定的内存地址空间，进程的创建和销毁不仅需要保存寄存器和栈信息，还需要资源的分配回收以及页调度，开销较大；线程只需要保存寄存器和栈信息，开销较小。</p></li></ul><p>另外一个重要区别是，<strong>进程是操作系统进行资源分配的基本单位，而线程是操作系统进行调度的基本单位</strong>，即CPU分配时间的单位。</p><h2 id="线程带来的好处" tabindex="-1"><a class="header-anchor" href="#线程带来的好处" aria-hidden="true">#</a> 线程带来的好处</h2><p>一直以来，硬件的发展极其迅速，也有一个很著名的"摩尔定律"，可能会奇怪明明讨论的是并发编程为什么会扯到了硬件的发展，这其中的关系应该是多核CPU的发展为并发编程提供的硬件基础。</p><p>摩尔定律并不是一种自然法则或者是物理定律，它只是基于认为观测数据后，对未来的一种预测。按照所预测的速度，我们的计算能力会按照指数级别的速度增长，不久以后会拥有超强的计算能力，正是在畅想未来的时候，2004年，Intel宣布4GHz芯片的计划推迟到2005年，然后在2004年秋季，Intel宣布彻底取消4GHz的计划，也就是说摩尔定律的有效性超过了半个世纪戛然而止。但是，聪明的硬件工程师并没有停止研发的脚步，他们为了进一步提升计算速度，而不是再追求单独的计算单元，而是将多个计算单元整合到了一起，也就是形成了多核CPU。</p><p>短短十几年的时间，家用型CPU,比如Intel i7就可以达到4核心甚至8核心。而专业服务器则通常可以达到几个独立的CPU，每一个CPU甚至拥有多达8个以上的内核。因此，摩尔定律似乎在CPU核心扩展上继续得到体验。因此，多核的CPU的背景下，催生了并发编程的趋势，通过<strong>并发编程的形式可以将多核CPU的计算能力发挥到极致，性能得到提升</strong>。</p><p>顶级计算机科学家Donald Ervin Knuth如此评价这种情况：在我看来，这种现象（并发）或多或少是由于硬件设计者无计可施了导致的，他们将摩尔定律的责任推给了软件开发者。</p><p>另外，在特殊的业务场景下先天的就适合于并发编程。比如在图像处理领域，一张1024X768像素的图片，包含达到78万6千多个像素。即时将所有的像素遍历一边都需要很长的时间，面对如此复杂的计算量就需要充分利用多核的计算的能力。又比如当我们在网上购物时，为了提升响应速度，需要拆分，减库存，生成订单等等这些操作，就可以进行拆分利用多线程的技术完成。<strong>面对复杂业务模型，并行程序会比串行程序更适应业务需求，而并发编程更能吻合这种业务拆分</strong> 。正是因为这些优点，使得多线程技术能够得到重视，也是一名CS学习者应该掌握的：</p><ul><li>充分利用多核CPU的计算能力；</li><li>方便进行业务拆分，提升应用性能</li></ul><hr><blockquote><p>编辑：沉默王二，内容大部分来源以下三个开源仓库：</p><ul><li><a href="http://concurrent.redspider.group/" target="_blank" rel="noopener noreferrer">深入浅出 Java 多线程<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewbox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a></li><li><a href="https://github.com/CL0610/Java-concurrency" target="_blank" rel="noopener noreferrer">并发编程知识总结<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" 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