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<p class='location'>Trait UnsafeNotify</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.clone_raw">clone_raw</a><a href="#tymethod.drop_raw">drop_raw</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>futures</a>::<wbr><a href='index.html'>executor</a></p><script>window.sidebarCurrent = {name: 'UnsafeNotify', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>futures</a>::<wbr><a href='index.html'>executor</a>::<wbr><a class="trait" href=''>UnsafeNotify</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a class='srclink' href='../../src/futures/task_impl/mod.rs.html#530-572' title='goto source code'>[src]</a></span></h1>
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<pre class='rust trait'>pub unsafe trait UnsafeNotify: <a class="trait" href="../../futures/executor/trait.Notify.html" title="trait futures::executor::Notify">Notify</a> {
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unsafe fn <a href='#tymethod.clone_raw' class='fnname'>clone_raw</a>(&self) -> <a class="struct" href="../../futures/executor/struct.NotifyHandle.html" title="struct futures::executor::NotifyHandle">NotifyHandle</a>;
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<div class='item-spacer'></div> unsafe fn <a href='#tymethod.drop_raw' class='fnname'>drop_raw</a>(&self);
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}</pre><div class='docblock'><p>An unsafe trait for implementing custom forms of memory management behind a
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<code>Task</code>.</p>
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<p>The <code>futures</code> critically relies on "notification handles" to extract for
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futures to contain and then later inform that they're ready to make
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progress. These handles, however, must be cheap to create and cheap
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to clone to ensure that this operation is efficient throughout the
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execution of a program.</p>
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<p>Typically this sort of memory management is done in the standard library
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with the <code>Arc</code> type. An <code>Arc</code> is relatively cheap to allocate an is
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quite cheap to clone and pass around. Plus, it's 100% safe!</p>
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<p>When working outside the standard library, however, you don't always have
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and <code>Arc</code> type available to you. This trait, <code>UnsafeNotify</code>, is intended
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to be the "unsafe version" of the <code>Notify</code> trait. This trait encodes the
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memory management operations of a <code>Task</code>'s notification handle, allowing
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custom implementations for the memory management of a notification handle.</p>
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<p>Put another way, the core notification type in this library,
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<code>NotifyHandle</code>, simply internally contains an instance of
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<code>*mut UnsafeNotify</code>. This "unsafe trait object" is then used exclusively
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to operate with, dynamically dispatching calls to clone, drop, and notify.
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Critically though as a raw pointer it doesn't require a particular form
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of memory management, allowing external implementations.</p>
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<p>A default implementation of the <code>UnsafeNotify</code> trait is provided for the
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<code>Arc</code> type in the standard library. If the <code>use_std</code> feature of this crate
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is not available however, you'll be required to implement your own
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instance of this trait to pass it into <code>NotifyHandle::new</code>.</p>
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<h1 id="unsafety" class="section-header"><a href="#unsafety">Unsafety</a></h1>
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<p>This trait is manually encoding the memory management of the underlying
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handle, and as a result is quite unsafe to implement! Implementors of
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this trait must guarantee:</p>
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<ul>
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<li>Calls to <code>clone_raw</code> produce uniquely owned handles. It should be safe
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to drop the current handle and have the returned handle still be valid.</li>
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<li>Calls to <code>drop_raw</code> work with <code>self</code> as a raw pointer, deallocating
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resources associated with it. This is a pretty unsafe operation as it's
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invalidating the <code>self</code> pointer, so extreme care needs to be taken.</li>
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</ul>
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<p>In general it's recommended to review the trait documentation as well as
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the implementation for <code>Arc</code> in this crate. When in doubt ping the
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<code>futures</code> authors to clarify an unsafety question here.</p>
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</div>
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<h2 id='required-methods' class='small-section-header'>
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Required Methods<a href='#required-methods' class='anchor'></a>
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</h2>
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<div class='methods'>
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<h3 id='tymethod.clone_raw' class='method'><span id='clone_raw.v' class='invisible'><code>unsafe fn <a href='#tymethod.clone_raw' class='fnname'>clone_raw</a>(&self) -> <a class="struct" href="../../futures/executor/struct.NotifyHandle.html" title="struct futures::executor::NotifyHandle">NotifyHandle</a></code></span></h3><div class='docblock'><p>Creates a new <code>NotifyHandle</code> from this instance of <code>UnsafeNotify</code>.</p>
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<p>This function will create a new uniquely owned handle that under the
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hood references the same notification instance. In other words calls
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to <code>notify</code> on the returned handle should be equivalent to calls to
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<code>notify</code> on this handle.</p>
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<h1 id="unsafety-1" class="section-header"><a href="#unsafety-1">Unsafety</a></h1>
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<p>This trait is unsafe to implement, as are all these methods. This
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method is also unsafe to call as it's asserting the <code>UnsafeNotify</code>
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value is in a consistent state. In general it's recommended to
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review the trait documentation as well as the implementation for <code>Arc</code>
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in this crate. When in doubt ping the <code>futures</code> authors to clarify
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an unsafety question here.</p>
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</div><h3 id='tymethod.drop_raw' class='method'><span id='drop_raw.v' class='invisible'><code>unsafe fn <a href='#tymethod.drop_raw' class='fnname'>drop_raw</a>(&self)</code></span></h3><div class='docblock'><p>Drops this instance of <code>UnsafeNotify</code>, deallocating resources
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associated with it.</p>
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<p>This method is intended to have a signature such as:</p>
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<div class='information'><div class='tooltip ignore'>ⓘ<span class='tooltiptext'>This example is not tested</span></div></div><pre class="rust rust-example-rendered ignore">
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<span class="kw">fn</span> <span class="ident">drop_raw</span>(<span class="self">self</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="self">Self</span>);</pre>
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<p>Unfortunately in Rust today that signature is not object safe.
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Nevertheless it's recommended to implement this function <em>as if</em> that
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were its signature. As such it is not safe to call on an invalid
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pointer, nor is the validity of the pointer guaranteed after this
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function returns.</p>
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<h1 id="unsafety-2" class="section-header"><a href="#unsafety-2">Unsafety</a></h1>
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<p>This trait is unsafe to implement, as are all these methods. This
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method is also unsafe to call as it's asserting the <code>UnsafeNotify</code>
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value is in a consistent state. In general it's recommended to
|
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review the trait documentation as well as the implementation for <code>Arc</code>
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||
in this crate. When in doubt ping the <code>futures</code> authors to clarify
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an unsafety question here.</p>
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</div></div>
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