Update future interrupts example in README

Summary: Updated the future interrupts example to get rid of the shared pointer circular reference problem

Reviewed By: djwatson

Differential Revision: D4360037

fbshipit-source-id: cb959929a508df4dcf3b81d01012bc55044a0b17

diff --git a/folly/futures/README.md b/folly/futures/README.md
index 381070e54f193d53f133c4fea0469be38148113e..ec50fa8d1fbec2f4351dd994462cc427de4350fb 100644 (file)
--- a/folly/futures/README.md
+++ b/folly/futures/README.md
@@ -824,13 +824,19 @@ Although inspired by the C++11 std::future interface, it is not a drop-in replac
 <p>Interrupts allow Future holders to send signals in the form of exceptions to Promise holders, who are free to handle the interrupt as they please (or not at all). For example:</p>
 
 <div class="remarkup-code-block" data-code-lang="cpp"><pre class="remarkup-code"><span class="k">auto</span><span class=""> </span><span class="n">p</span><span class=""> </span><span class="o">=</span><span class=""> </span><span class="n">std</span><span class="o">:</span><span class="o">:</span><span class="n">make_shared</span><span class="o">&lt;</span><span class="n">Promise</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="o">&gt;</span><span class="p">(</span><span class="p">)</span><span class="p">;</span><span class="">
-</span><span class="n">p</span><span class="o">-</span><span class="o">&gt;</span><span class="n">setInterruptHandler</span><span class="p">(</span><span class="p">[</span><span class="n">p</span><span class="p">]</span><span class="p">(</span><span class="k">const</span><span class=""> </span><span class="n">exception_wrapper</span><span class="o">&amp;</span><span class=""> </span><span class="n">e</span><span class="p">)</span><span class="p">&#123;</span><span class="">
+</span><span class="n">p</span><span class="o">-</span><span class="o">&gt;</span><span class="n">setInterruptHandler</span><span class="p">(</span><span class="p">[</span><span class="n">weakPromise</span><span class=""> </span><span class="o">=</span><span class=""> </span><span class="n">folly</span><span class="o">:</span><span class="o">:</span><span class="n">to_weak_ptr</span><span class="p">(</span><span class="n">p</span><span class="p">)</span><span class="p">]</span><span class="p">(</span><span class="">
+</span><span class="">    </span><span class="k">const</span><span class=""> </span><span class="n">exception_wrapper</span><span class="o">&amp;</span><span class=""> </span><span class="n">e</span><span class="p">)</span><span class=""> </span><span class="p">&#123;</span><span class="">
+</span><span class="">  </span><span class="k">auto</span><span class=""> </span><span class="n">promise</span><span class=""> </span><span class="o">=</span><span class=""> </span><span class="n">weakPromise</span><span class="p">.</span><span class="n">lock</span><span class="p">(</span><span class="p">)</span><span class="p">;</span><span class="">
 </span><span class="">  </span><span class="c1">// Handle the interrupt. For instance, we could just fulfill the Promise
 </span><span class="">  </span><span class="c1">// with the given exception:
-</span><span class="">  </span><span class="n">p</span><span class="o">-</span><span class="o">&gt;</span><span class="n">setException</span><span class="p">(</span><span class="n">e</span><span class="p">)</span><span class="p">;</span><span class="">
-</span><span class="">  
-  </span><span class="c1">// Or maybe we want the Future to complete with some special value
-</span><span class="">  </span><span class="n">p</span><span class="o">-</span><span class="o">&gt;</span><span class="n">setValue</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span><span class="p">;</span><span class="">
+</span><span class="">  </span><span class="k">if</span><span class=""> </span><span class="p">(</span><span class="n">promise</span><span class="p">)</span><span class=""> </span><span class="p">&#123;</span><span class="">
+</span><span class="">    </span><span class="n">promise</span><span class="o">-</span><span class="o">&gt;</span><span class="n">setException</span><span class="p">(</span><span class="n">e</span><span class="p">)</span><span class="p">;</span><span class="">
+</span><span class="">  </span><span class="p">&#125;</span><span class="">
+</span><span class="">
+</span><span class="">  </span><span class="c1">// Or maybe we want the Future to complete with some special value
+</span><span class="">  </span><span class="k">if</span><span class=""> </span><span class="p">(</span><span class="n">promise</span><span class="p">)</span><span class=""> </span><span class="p">&#123;</span><span class="">
+</span><span class="">    </span><span class="n">promise</span><span class="o">-</span><span class="o">&gt;</span><span class="n">setValue</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span><span class="p">;</span><span class="">
+</span><span class="">  </span><span class="p">&#125;</span><span class="">
 </span><span class="">
 </span><span class="">  </span><span class="c1">// Or maybe we don&#039;t want to do anything at all! Including not setting
 </span><span class="">  </span><span class="c1">// this handler in the first place.