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+ caml_release_runtime_system导致的死锁问题
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+ Jun 28, 2023
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+ <p>给出一个<code>test.ml</code>:</p>
+<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">Printf</span>.eprintf <span class="string">&quot;hello from OCaml\n%!&quot;</span></span><br></pre></td></tr></table></figure>
+
+<p>和<code>test-ocaml-5.c</code>:</p>
+<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdlib.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;caml/misc.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;caml/callback.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;caml/threads.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="type">int</span></span><br><span class="line"><span class="title function_">main</span> <span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line"> &#123;</span><br><span class="line"> <span class="built_in">fprintf</span> (<span class="built_in">stderr</span>, <span class="string">&quot;starting up ...\n&quot;</span>);</span><br><span class="line"> caml_startup (argv);</span><br><span class="line"> <span class="built_in">fprintf</span> (<span class="built_in">stderr</span>, <span class="string">&quot;acquiring ...\n&quot;</span>);</span><br><span class="line"> caml_acquire_runtime_system ();</span><br><span class="line"> <span class="built_in">fprintf</span> (<span class="built_in">stderr</span>, <span class="string">&quot;acquired\n&quot;</span>);</span><br><span class="line"> <span class="comment">// here is where I would be calling an OCaml callback</span></span><br><span class="line"> <span class="comment">// omitted for simplicity</span></span><br><span class="line"> caml_release_runtime_system ();</span><br><span class="line"> <span class="built_in">exit</span> (<span class="number">0</span>);</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
+
+<p>然后用OCaml5的ocaml native compiler编译一下(这里我用的是<code>ocaml-variants.5.0.0+options</code>):<br><code>ocamlopt -g test-ocaml-5.c test.ml -o test-ocaml-5</code></p>
+<p>运行<code>test-ocaml-5</code> 会出现:</p>
+<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">starting up ...</span><br><span class="line">hello from OCaml</span><br><span class="line">acquiring ...</span><br><span class="line">Fatal error: Fatal error during lock: Resource deadlock avoided</span><br><span class="line"></span><br><span class="line">[1] 8998 IOT instruction (core dumped) ./test-ocaml-5</span><br></pre></td></tr></table></figure>
+
+<p>这里我尝试了一下 4.14.0 和 4.14.1 , 都没有出现这个情况,而如果用<code>threads</code>编译的话:<br><code>ocamlopt -g -I +unix unix.cmxa -I +threads threads.cmxa test-ocaml-5.c test.ml -o test-ocaml-5</code></p>
+<p>无论在5.0还是4.14.x,都会挂起。</p>
+<p>出现这个问题的一个可能原因是,在<code>test-ocaml-5.c</code>中,我在开头调用了<code>caml_startup()</code>,这会让当前线程获取锁,而<code>caml_acquire_runtime_system()</code>会再次获取它,<code>caml_acquire_runtime_system()</code> 应该在<code>caml_release_runtime_system()</code>之后调用:</p>
+<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">int</span></span><br><span class="line">main (<span class="built_in">int</span> argc, <span class="built_in">char</span> *argv<span class="literal">[]</span>)</span><br><span class="line"> &#123;</span><br><span class="line"> fprintf (stderr, <span class="string">&quot;starting up ...\n&quot;</span>);</span><br><span class="line"> caml_startup (argv);</span><br><span class="line"> fprintf (stderr, <span class="string">&quot;acquiring ...\n&quot;</span>);</span><br><span class="line"> caml_release_runtime_system <span class="literal">()</span>;</span><br><span class="line"> caml_acquire_runtime_system <span class="literal">()</span>;</span><br><span class="line"> fprintf (stderr, <span class="string">&quot;acquired\n&quot;</span>);</span><br><span class="line"> exit (<span class="number">0</span>);</span><br><span class="line"> &#125;</span><br></pre></td></tr></table></figure>
+
+<p>运行结果为:</p>
+<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">starting up ...</span><br><span class="line">hello from OCaml</span><br><span class="line">acquiring ...</span><br><span class="line">acquired</span><br></pre></td></tr></table></figure>
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