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<p class='location'>Trait Sync</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>marker</a></p><script>window.sidebarCurrent = {name: 'Sync', 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'>core</a>::<wbr><a href='index.html'>marker</a>::<wbr><a class="trait" href=''>Sync</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'>
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
[<span class='inner'>−</span>]
</a>
</span><a class='srclink' href='../../src/core/marker.rs.html#343-345' title='goto source code'>[src]</a></span></h1>
<pre class='rust trait'><div class="docblock attributes">#[lang = "sync"]
</div>pub unsafe auto trait Sync { }</pre><div class='docblock'><p>Types for which it is safe to share references between threads.</p>
<p>This trait is automatically implemented when the compiler determines
it's appropriate.</p>
<p>The precise definition is: a type <code>T</code> is <code>Sync</code> if <code>&T</code> is
<a href="trait.Send.html"><code>Send</code></a>. In other words, if there is no possibility of
<a href="../../reference/behavior-considered-undefined.html">undefined behavior</a> (including data races) when passing
<code>&T</code> references between threads.</p>
<p>As one would expect, primitive types like <a href="../../std/primitive.u8.html"><code>u8</code></a> and <a href="../../std/primitive.f64.html"><code>f64</code></a>
are all <code>Sync</code>, and so are simple aggregate types containing them,
like tuples, structs and enums. More examples of basic <code>Sync</code>
types include "immutable" types like <code>&T</code>, and those with simple
inherited mutability, such as <a href="../../std/boxed/struct.Box.html"><code>Box<T></code></a>, <a href="../../std/vec/struct.Vec.html"><code>Vec<T></code></a> and
most other collection types. (Generic parameters need to be <code>Sync</code>
for their container to be <code>Sync</code>.)</p>
<p>A somewhat surprising consequence of the definition is that <code>&mut T</code>
is <code>Sync</code> (if <code>T</code> is <code>Sync</code>) even though it seems like that might
provide unsynchronized mutation. The trick is that a mutable
reference behind a shared reference (that is, <code>& &mut T</code>)
becomes read-only, as if it were a <code>& &T</code>. Hence there is no risk
of a data race.</p>
<p>Types that are not <code>Sync</code> are those that have "interior
mutability" in a non-thread-safe form, such as <a href="../cell/struct.Cell.html"><code>cell::Cell</code></a>
and <a href="../cell/struct.RefCell.html"><code>cell::RefCell</code></a>. These types allow for mutation of
their contents even through an immutable, shared reference. For
example the <code>set</code> method on <a href="../cell/struct.Cell.html"><code>Cell<T></code></a> takes <code>&self</code>, so it requires
only a shared reference <a href="../cell/struct.Cell.html"><code>&Cell<T></code></a>. The method performs no
synchronization, thus <a href="../cell/struct.Cell.html"><code>Cell</code></a> cannot be <code>Sync</code>.</p>
<p>Another example of a non-<code>Sync</code> type is the reference-counting
pointer <a href="../../std/rc/struct.Rc.html"><code>rc::Rc</code></a>. Given any reference <a href="../../std/rc/struct.Rc.html"><code>&Rc<T></code></a>, you can clone
a new <a href="../../std/rc/struct.Rc.html"><code>Rc<T></code></a>, modifying the reference counts in a non-atomic way.</p>
<p>For cases when one does need thread-safe interior mutability,
Rust provides <a href="../sync/atomic/index.html">atomic data types</a>, as well as explicit locking via
<a href="../../std/sync/struct.Mutex.html"><code>sync::Mutex</code></a> and <a href="../../std/sync/struct.RwLock.html"><code>sync::RwLock</code></a>. These types
ensure that any mutation cannot cause data races, hence the types
are <code>Sync</code>. Likewise, <a href="../../std/sync/struct.Arc.html"><code>sync::Arc</code></a> provides a thread-safe
analogue of <a href="../../std/rc/struct.Rc.html"><code>Rc</code></a>.</p>
<p>Any types with interior mutability must also use the
<a href="../cell/struct.UnsafeCell.html"><code>cell::UnsafeCell</code></a> wrapper around the value(s) which
can be mutated through a shared reference. Failing to doing this is
<a href="../../reference/behavior-considered-undefined.html">undefined behavior</a>. For example, <a href="../../std/mem/fn.transmute.html"><code>transmute</code></a>-ing
from <code>&T</code> to <code>&mut T</code> is invalid.</p>
<p>See <a href="../../nomicon/send-and-sync.html">the Nomicon</a> for more
details about <code>Sync</code>.</p>
</div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/ptr.rs.html#2365' title='goto source code'>[src]</a></div><code>impl<T: <a class="trait" href="../../core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> Sync for <a class="struct" href="../../core/ptr/struct.Unique.html" title="struct core::ptr::Unique">Unique</a><T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/ptr.rs.html#2498' title='goto source code'>[src]</a></div><code>impl<T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> !Sync for <a class="struct" href="../../core/ptr/struct.NonNull.html" title="struct core::ptr::NonNull">NonNull</a><T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/marker.rs.html#348' title='goto source code'>[src]</a></div><code>impl<T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> !Sync for *const T</code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/marker.rs.html#350' title='goto source code'>[src]</a></div><code>impl<T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> !Sync for *mut T</code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#142' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicBool.html" title="struct core::sync::atomic::AtomicBool">AtomicBool</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#167' title='goto source code'>[src]</a></div><code>impl<T> Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicPtr.html" title="struct core::sync::atomic::AtomicPtr">AtomicPtr</a><T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicI8.html" title="struct core::sync::atomic::AtomicI8">AtomicI8</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicU8.html" title="struct core::sync::atomic::AtomicU8">AtomicU8</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicI16.html" title="struct core::sync::atomic::AtomicI16">AtomicI16</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicU16.html" title="struct core::sync::atomic::AtomicU16">AtomicU16</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicI32.html" title="struct core::sync::atomic::AtomicI32">AtomicI32</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicU32.html" title="struct core::sync::atomic::AtomicU32">AtomicU32</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicI64.html" title="struct core::sync::atomic::AtomicI64">AtomicI64</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicU64.html" title="struct core::sync::atomic::AtomicU64">AtomicU64</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicIsize.html" title="struct core::sync::atomic::AtomicIsize">AtomicIsize</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/sync/atomic.rs.html#1000' title='goto source code'>[src]</a></div><code>impl Sync for <a class="struct" href="../../core/sync/atomic/struct.AtomicUsize.html" title="struct core::sync::atomic::AtomicUsize">AtomicUsize</a></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/cell.rs.html#248' title='goto source code'>[src]</a></div><code>impl<T> !Sync for <a class="struct" href="../../core/cell/struct.Cell.html" title="struct core::cell::Cell">Cell</a><T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/cell.rs.html#862' title='goto source code'>[src]</a></div><code>impl<T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> !Sync for <a class="struct" href="../../core/cell/struct.RefCell.html" title="struct core::cell::RefCell">RefCell</a><T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/cell.rs.html#1200' title='goto source code'>[src]</a></div><code>impl<T: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> !Sync for <a class="struct" href="../../core/cell/struct.UnsafeCell.html" title="struct core::cell::UnsafeCell">UnsafeCell</a><T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/slice/mod.rs.html#1406' title='goto source code'>[src]</a></div><code>impl<'a, T: <a class="trait" href="../../core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a>> Sync for <a class="struct" href="../../core/slice/struct.Iter.html" title="struct core::slice::Iter">Iter</a><'a, T></code></li>
<li><div class='out-of-band'><a class='srclink' href='../../src/core/slice/mod.rs.html#1523' title='goto source code'>[src]</a></div><code>impl<'a, T: <a class="trait" href="../../core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a>> Sync for <a class="struct" href="../../core/slice/struct.IterMut.html" title="struct core::slice::IterMut">IterMut</a><'a, T></code></li>
</ul><script type="text/javascript" async
src="../../implementors/core/marker/trait.Sync.js">
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