http://chestnutheng.github.io/tags/redis/ Recent content in Redis on 子恒的博客 Hugo zh-CN Thu, 24 Sep 2020 15:57:32 +0800 http://chestnutheng.github.io/redis_1/ Thu, 24 Sep 2020 15:57:27 +0800 http://chestnutheng.github.io/redis_1/ <h1 id="分布式锁">分布式锁</h1> <h2 id="简单加锁">简单加锁</h2> <div class="highlight"><div class="chroma"> <table class="lntable"><tr><td class="lntd"> <pre tabindex="0" class="chroma"><code><span class="lnt">1 </span><span class="lnt">2 </span><span class="lnt">3 </span><span class="lnt">4 </span><span class="lnt">5 </span></code></pre></td> <td class="lntd"> <pre tabindex="0" class="chroma"><code class="language-fallback" data-lang="fallback"><span class="line"><span class="cl">// 思想：利用setnx检测有没有set过，如果set过就表示没有抢到锁 </span></span><span class="line"><span class="cl">&gt; setnx locker true </span></span><span class="line"><span class="cl">OK </span></span><span class="line"><span class="cl">// ... do somthing ... </span></span><span class="line"><span class="cl">&gt; del locker </span></span></code></pre></td></tr></table> </div> </div><h2 id="处理set之后进程崩溃的死锁问题">处理set之后进程崩溃的死锁问题</h2> <div class="highlight"><div class="chroma"> <table class="lntable"><tr><td class="lntd"> <pre tabindex="0" class="chroma"><code><span class="lnt">1 </span><span class="lnt">2 </span><span class="lnt">3 </span><span class="lnt">4 </span><span class="lnt">5 </span><span class="lnt">6 </span></code></pre></td> <td class="lntd"> <pre tabindex="0" class="chroma"><code class="language-fallback" data-lang="fallback"><span class="line"><span class="cl">// 思想：给锁加上过期时间，即使set之后进程挂掉，也不会死锁 </span></span><span class="line"><span class="cl">&gt; setnx locker true </span></span><span class="line"><span class="cl">OK </span></span><span class="line"><span class="cl">&gt; expire locker 5 </span></span><span class="line"><span class="cl">// ... do somthing ... </span></span><span class="line"><span class="cl">&gt; del locker </span></span></code></pre></td></tr></table> </div> </div><h2 id="处理非原子性问题">处理非原子性问题</h2> <p>setnx之后，expire之前，进程挂了，也会死锁。怎么处理这种情况？</p> <ol> <li>使用redis事务吗？事务里没有if else，要么全部执行，要么全部不执行。需求是setnx成功才执行expire，有依赖关系，没法用事务</li> <li>使用新的原子命令，如下</li> </ol> <div class="highlight"><div class="chroma"> <table class="lntable"><tr><td class="lntd"> <pre tabindex="0" class="chroma"><code><span class="lnt">1 </span><span class="lnt">2 </span><span class="lnt">3 </span><span class="lnt">4 </span></code></pre></td> <td class="lntd"> <pre tabindex="0" class="chroma"><code class="language-fallback" data-lang="fallback"><span class="line"><span class="cl">&gt; set locker true ex5 nx </span></span><span class="line"><span class="cl">OK </span></span><span class="line"><span class="cl">// ... do somthing ... </span></span><span class="line"><span class="cl">&gt; del locker </span></span></code></pre></td></tr></table> </div> </div><h2 id="处理超时问题">处理超时问题</h2> <p>上面的方案设定了超时时间。但是如果少数操作的时间超过了超时时间怎么办？有两个问题：</p>