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</pre><pre class="rust">
<span class="kw">use</span> <span class="ident">core::fmt</span>;
<span class="kw">use</span> <span class="ident">core::mem</span>;
<span class="kw">use</span> <span class="ident">scopeguard::defer</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::atomic::Shared</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::collector::Collector</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::deferred::Deferred</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::internal::Local</span>;
<span class="doccomment">/// A guard that keeps the current thread pinned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Pinning</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The current thread is pinned by calling [`pin`], which returns a new guard:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch as epoch;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // It is often convenient to prefix a call to `pin` with a `&` in order to create a reference.</span>
<span class="doccomment">/// // This is not really necessary, but makes passing references to the guard a bit easier.</span>
<span class="doccomment">/// let guard = &epoch::pin();</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When a guard gets dropped, the current thread is automatically unpinned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Pointers on the stack</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Having a guard allows us to create pointers on the stack to heap-allocated objects.</span>
<span class="doccomment">/// For example:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic};</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::SeqCst;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Create a heap-allocated number.</span>
<span class="doccomment">/// let a = Atomic::new(777);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Pin the current thread.</span>
<span class="doccomment">/// let guard = &epoch::pin();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Load the heap-allocated object and create pointer `p` on the stack.</span>
<span class="doccomment">/// let p = a.load(SeqCst, guard);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Dereference the pointer and print the value:</span>
<span class="doccomment">/// if let Some(num) = unsafe { p.as_ref() } {</span>
<span class="doccomment">/// println!("The number is {}.", num);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Multiple guards</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Pinning is reentrant and it is perfectly legal to create multiple guards. In that case, the</span>
<span class="doccomment">/// thread will actually be pinned only when the first guard is created and unpinned when the last</span>
<span class="doccomment">/// one is dropped:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch as epoch;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let guard1 = epoch::pin();</span>
<span class="doccomment">/// let guard2 = epoch::pin();</span>
<span class="doccomment">/// assert!(epoch::is_pinned());</span>
<span class="doccomment">/// drop(guard1);</span>
<span class="doccomment">/// assert!(epoch::is_pinned());</span>
<span class="doccomment">/// drop(guard2);</span>
<span class="doccomment">/// assert!(!epoch::is_pinned());</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`pin`]: super::pin</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Guard</span> {
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="ident">local</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Local</span>,
}
<span class="kw">impl</span> <span class="ident">Guard</span> {
<span class="doccomment">/// Stores a function so that it can be executed at some point after all currently pinned</span>
<span class="doccomment">/// threads get unpinned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method first stores `f` into the thread-local (or handle-local) cache. If this cache</span>
<span class="doccomment">/// becomes full, some functions are moved into the global cache. At the same time, some</span>
<span class="doccomment">/// functions from both local and global caches may get executed in order to incrementally</span>
<span class="doccomment">/// clean up the caches as they fill up.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There is no guarantee when exactly `f` will be executed. The only guarantee is that it</span>
<span class="doccomment">/// won't be executed until all currently pinned threads get unpinned. In theory, `f` might</span>
<span class="doccomment">/// never run, but the epoch-based garbage collection will make an effort to execute it</span>
<span class="doccomment">/// reasonably soon.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, the function will simply be</span>
<span class="doccomment">/// executed immediately.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">defer</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>)
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-</span><span class="op">></span> <span class="ident">R</span>,
<span class="ident">F</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'static</span>,
{
<span class="kw">unsafe</span> {
<span class="self">self</span>.<span class="ident">defer_unchecked</span>(<span class="ident">f</span>);
}
}
<span class="doccomment">/// Stores a function so that it can be executed at some point after all currently pinned</span>
<span class="doccomment">/// threads get unpinned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method first stores `f` into the thread-local (or handle-local) cache. If this cache</span>
<span class="doccomment">/// becomes full, some functions are moved into the global cache. At the same time, some</span>
<span class="doccomment">/// functions from both local and global caches may get executed in order to incrementally</span>
<span class="doccomment">/// clean up the caches as they fill up.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There is no guarantee when exactly `f` will be executed. The only guarantee is that it</span>
<span class="doccomment">/// won't be executed until all currently pinned threads get unpinned. In theory, `f` might</span>
<span class="doccomment">/// never run, but the epoch-based garbage collection will make an effort to execute it</span>
<span class="doccomment">/// reasonably soon.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, the function will simply be</span>
<span class="doccomment">/// executed immediately.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The given function must not hold reference onto the stack. It is highly recommended that</span>
<span class="doccomment">/// the passed function is **always** marked with `move` in order to prevent accidental</span>
<span class="doccomment">/// borrows.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch as epoch;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let guard = &epoch::pin();</span>
<span class="doccomment">/// let message = "Hello!";</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// // ALWAYS use `move` when sending a closure into `defer_unchecked`.</span>
<span class="doccomment">/// guard.defer_unchecked(move || {</span>
<span class="doccomment">/// println!("{}", message);</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Apart from that, keep in mind that another thread may execute `f`, so anything accessed by</span>
<span class="doccomment">/// the closure must be `Send`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// We intentionally didn't require `F: Send`, because Rust's type systems usually cannot prove</span>
<span class="doccomment">/// `F: Send` for typical use cases. For example, consider the following code snippet, which</span>
<span class="doccomment">/// exemplifies the typical use case of deferring the deallocation of a shared reference:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore</span>
<span class="doccomment">/// let shared = Owned::new(7i32).into_shared(guard);</span>
<span class="doccomment">/// guard.defer_unchecked(move || shared.into_owned()); // `Shared` is not `Send`!</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// While `Shared` is not `Send`, it's safe for another thread to call the deferred function,</span>
<span class="doccomment">/// because it's called only after the grace period and `shared` is no longer shared with other</span>
<span class="doccomment">/// threads. But we don't expect type systems to prove this.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When a heap-allocated object in a data structure becomes unreachable, it has to be</span>
<span class="doccomment">/// deallocated. However, the current thread and other threads may be still holding references</span>
<span class="doccomment">/// on the stack to that same object. Therefore it cannot be deallocated before those references</span>
<span class="doccomment">/// get dropped. This method can defer deallocation until all those threads get unpinned and</span>
<span class="doccomment">/// consequently drop all their references on the stack.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic, Owned};</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::SeqCst;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let a = Atomic::new("foo");</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Now suppose that `a` is shared among multiple threads and concurrently</span>
<span class="doccomment">/// // accessed and modified...</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Pin the current thread.</span>
<span class="doccomment">/// let guard = &epoch::pin();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Steal the object currently stored in `a` and swap it with another one.</span>
<span class="doccomment">/// let p = a.swap(Owned::new("bar").into_shared(guard), SeqCst, guard);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// if !p.is_null() {</span>
<span class="doccomment">/// // The object `p` is pointing to is now unreachable.</span>
<span class="doccomment">/// // Defer its deallocation until all currently pinned threads get unpinned.</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// // ALWAYS use `move` when sending a closure into `defer_unchecked`.</span>
<span class="doccomment">/// guard.defer_unchecked(move || {</span>
<span class="doccomment">/// println!("{} is now being deallocated.", p.deref());</span>
<span class="doccomment">/// // Now we have unique access to the object pointed to by `p` and can turn it</span>
<span class="doccomment">/// // into an `Owned`. Dropping the `Owned` will deallocate the object.</span>
<span class="doccomment">/// drop(p.into_owned());</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">defer_unchecked</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>)
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-</span><span class="op">></span> <span class="ident">R</span>,
{
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">local</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>() {
<span class="ident">local</span>.<span class="ident">defer</span>(<span class="ident">Deferred::new</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> <span class="ident">drop</span>(<span class="ident">f</span>())), <span class="self">self</span>);
} <span class="kw">else</span> {
<span class="ident">drop</span>(<span class="ident">f</span>());
}
}
<span class="doccomment">/// Stores a destructor for an object so that it can be deallocated and dropped at some point</span>
<span class="doccomment">/// after all currently pinned threads get unpinned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method first stores the destructor into the thread-local (or handle-local) cache. If</span>
<span class="doccomment">/// this cache becomes full, some destructors are moved into the global cache. At the same</span>
<span class="doccomment">/// time, some destructors from both local and global caches may get executed in order to</span>
<span class="doccomment">/// incrementally clean up the caches as they fill up.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There is no guarantee when exactly the destructor will be executed. The only guarantee is</span>
<span class="doccomment">/// that it won't be executed until all currently pinned threads get unpinned. In theory, the</span>
<span class="doccomment">/// destructor might never run, but the epoch-based garbage collection will make an effort to</span>
<span class="doccomment">/// execute it reasonably soon.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, the destructor will simply be</span>
<span class="doccomment">/// executed immediately.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The object must not be reachable by other threads anymore, otherwise it might be still in</span>
<span class="doccomment">/// use when the destructor runs.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Apart from that, keep in mind that another thread may execute the destructor, so the object</span>
<span class="doccomment">/// must be sendable to other threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// We intentionally didn't require `T: Send`, because Rust's type systems usually cannot prove</span>
<span class="doccomment">/// `T: Send` for typical use cases. For example, consider the following code snippet, which</span>
<span class="doccomment">/// exemplifies the typical use case of deferring the deallocation of a shared reference:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore</span>
<span class="doccomment">/// let shared = Owned::new(7i32).into_shared(guard);</span>
<span class="doccomment">/// guard.defer_destroy(shared); // `Shared` is not `Send`!</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// While `Shared` is not `Send`, it's safe for another thread to call the destructor, because</span>
<span class="doccomment">/// it's called only after the grace period and `shared` is no longer shared with other</span>
<span class="doccomment">/// threads. But we don't expect type systems to prove this.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When a heap-allocated object in a data structure becomes unreachable, it has to be</span>
<span class="doccomment">/// deallocated. However, the current thread and other threads may be still holding references</span>
<span class="doccomment">/// on the stack to that same object. Therefore it cannot be deallocated before those references</span>
<span class="doccomment">/// get dropped. This method can defer deallocation until all those threads get unpinned and</span>
<span class="doccomment">/// consequently drop all their references on the stack.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic, Owned};</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::SeqCst;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let a = Atomic::new("foo");</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Now suppose that `a` is shared among multiple threads and concurrently</span>
<span class="doccomment">/// // accessed and modified...</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Pin the current thread.</span>
<span class="doccomment">/// let guard = &epoch::pin();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Steal the object currently stored in `a` and swap it with another one.</span>
<span class="doccomment">/// let p = a.swap(Owned::new("bar").into_shared(guard), SeqCst, guard);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// if !p.is_null() {</span>
<span class="doccomment">/// // The object `p` is pointing to is now unreachable.</span>
<span class="doccomment">/// // Defer its deallocation until all currently pinned threads get unpinned.</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// guard.defer_destroy(p);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">defer_destroy</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">ptr</span>: <span class="ident">Shared</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span>) {
<span class="self">self</span>.<span class="ident">defer_unchecked</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> <span class="ident">ptr</span>.<span class="ident">into_owned</span>());
}
<span class="doccomment">/// Clears up the thread-local cache of deferred functions by executing them or moving into the</span>
<span class="doccomment">/// global cache.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Call this method after deferring execution of a function if you want to get it executed as</span>
<span class="doccomment">/// soon as possible. Flushing will make sure it is residing in in the global cache, so that</span>
<span class="doccomment">/// any thread has a chance of taking the function and executing it.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, it is a no-op (nothing happens).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch as epoch;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let guard = &epoch::pin();</span>
<span class="doccomment">/// guard.defer(move || {</span>
<span class="doccomment">/// println!("This better be printed as soon as possible!");</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// guard.flush();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">flush</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">local</span>) <span class="op">=</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>() } {
<span class="ident">local</span>.<span class="ident">flush</span>(<span class="self">self</span>);
}
}
<span class="doccomment">/// Unpins and then immediately re-pins the thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method is useful when you don't want delay the advancement of the global epoch by</span>
<span class="doccomment">/// holding an old epoch. For safety, you should not maintain any guard-based reference across</span>
<span class="doccomment">/// the call (the latter is enforced by `&mut self`). The thread will only be repinned if this</span>
<span class="doccomment">/// is the only active guard for the current thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, then the call will be just no-op.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic};</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::SeqCst;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let a = Atomic::new(777);</span>
<span class="doccomment">/// let mut guard = epoch::pin();</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let p = a.load(SeqCst, &guard);</span>
<span class="doccomment">/// assert_eq!(unsafe { p.as_ref() }, Some(&777));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// guard.repin();</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let p = a.load(SeqCst, &guard);</span>
<span class="doccomment">/// assert_eq!(unsafe { p.as_ref() }, Some(&777));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">repin</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">local</span>) <span class="op">=</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>() } {
<span class="ident">local</span>.<span class="ident">repin</span>();
}
}
<span class="doccomment">/// Temporarily unpins the thread, executes the given function and then re-pins the thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method is useful when you need to perform a long-running operation (e.g. sleeping)</span>
<span class="doccomment">/// and don't need to maintain any guard-based reference across the call (the latter is enforced</span>
<span class="doccomment">/// by `&mut self`). The thread will only be unpinned if this is the only active guard for the</span>
<span class="doccomment">/// current thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, then the passed function is called</span>
<span class="doccomment">/// directly without unpinning the thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic};</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::SeqCst;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">/// use std::time::Duration;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let a = Atomic::new(777);</span>
<span class="doccomment">/// let mut guard = epoch::pin();</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let p = a.load(SeqCst, &guard);</span>
<span class="doccomment">/// assert_eq!(unsafe { p.as_ref() }, Some(&777));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// guard.repin_after(|| thread::sleep(Duration::from_millis(50)));</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let p = a.load(SeqCst, &guard);</span>
<span class="doccomment">/// assert_eq!(unsafe { p.as_ref() }, Some(&777));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">repin_after</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-</span><span class="op">></span> <span class="ident">R</span>
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-</span><span class="op">></span> <span class="ident">R</span>,
{
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">local</span>) <span class="op">=</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>() } {
<span class="comment">// We need to acquire a handle here to ensure the Local doesn't</span>
<span class="comment">// disappear from under us.</span>
<span class="ident">local</span>.<span class="ident">acquire_handle</span>();
<span class="ident">local</span>.<span class="ident">unpin</span>();
}
<span class="comment">// Ensure the Guard is re-pinned even if the function panics</span>
<span class="macro">defer!</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">local</span>) <span class="op">=</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>() } {
<span class="ident">mem::forget</span>(<span class="ident">local</span>.<span class="ident">pin</span>());
<span class="ident">local</span>.<span class="ident">release_handle</span>();
}
}
<span class="ident">f</span>()
}
<span class="doccomment">/// Returns the `Collector` associated with this guard.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method is useful when you need to ensure that all guards used with</span>
<span class="doccomment">/// a data structure come from the same collector.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method is called from an [`unprotected`] guard, then `None` is returned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch as epoch;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let guard1 = epoch::pin();</span>
<span class="doccomment">/// let guard2 = epoch::pin();</span>
<span class="doccomment">/// assert!(guard1.collector() == guard2.collector());</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">collector</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Collector</span><span class="op">></span> {
<span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">local</span><span class="op">|</span> <span class="ident">local</span>.<span class="ident">collector</span>()) }
}
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Guard</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">local</span>) <span class="op">=</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">local</span>.<span class="ident">as_ref</span>() } {
<span class="ident">local</span>.<span class="ident">unpin</span>();
}
}
}
<span class="kw">impl</span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">Guard</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">pad</span>(<span class="string">"Guard { .. }"</span>)
}
}
<span class="doccomment">/// Returns a reference to a dummy guard that allows unprotected access to [`Atomic`]s.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This guard should be used in special occasions only. Note that it doesn't actually keep any</span>
<span class="doccomment">/// thread pinned - it's just a fake guard that allows loading from [`Atomic`]s unsafely.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that calling [`defer`] with a dummy guard will not defer the function - it will just</span>
<span class="doccomment">/// execute the function immediately.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If necessary, it's possible to create more dummy guards by cloning: `unprotected().clone()`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Loading and dereferencing data from an [`Atomic`] using this guard is safe only if the</span>
<span class="doccomment">/// [`Atomic`] is not being concurrently modified by other threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic};</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::Relaxed;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let a = Atomic::new(7);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// // Load `a` without pinning the current thread.</span>
<span class="doccomment">/// a.load(Relaxed, epoch::unprotected());</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // It's possible to create more dummy guards by calling `clone()`.</span>
<span class="doccomment">/// let dummy = &epoch::unprotected().clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// dummy.defer(move || {</span>
<span class="doccomment">/// println!("This gets executed immediately.");</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Dropping `dummy` doesn't affect the current thread - it's just a noop.</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The most common use of this function is when constructing or destructing a data structure.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For example, we can use a dummy guard in the destructor of a Treiber stack because at that</span>
<span class="doccomment">/// point no other thread could concurrently modify the [`Atomic`]s we are accessing.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If we were to actually pin the current thread during destruction, that would just unnecessarily</span>
<span class="doccomment">/// delay garbage collection and incur some performance cost, so in cases like these `unprotected`</span>
<span class="doccomment">/// is very helpful.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_epoch::{self as epoch, Atomic};</span>
<span class="doccomment">/// use std::mem::ManuallyDrop;</span>
<span class="doccomment">/// use std::sync::atomic::Ordering::Relaxed;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// struct Stack<T> {</span>
<span class="doccomment">/// head: Atomic<Node<T>>,</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// struct Node<T> {</span>
<span class="doccomment">/// data: ManuallyDrop<T>,</span>
<span class="doccomment">/// next: Atomic<Node<T>>,</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// impl<T> Drop for Stack<T> {</span>
<span class="doccomment">/// fn drop(&mut self) {</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// // Unprotected load.</span>
<span class="doccomment">/// let mut node = self.head.load(Relaxed, epoch::unprotected());</span>
<span class="doccomment">///</span>
<span class="doccomment">/// while let Some(n) = node.as_ref() {</span>
<span class="doccomment">/// // Unprotected load.</span>
<span class="doccomment">/// let next = n.next.load(Relaxed, epoch::unprotected());</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Take ownership of the node, then drop its data and deallocate it.</span>
<span class="doccomment">/// let mut o = node.into_owned();</span>
<span class="doccomment">/// ManuallyDrop::drop(&mut o.data);</span>
<span class="doccomment">/// drop(o);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// node = next;</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Atomic`]: super::Atomic</span>
<span class="doccomment">/// [`defer`]: Guard::defer</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">unprotected</span>() <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="lifetime">'static</span> <span class="ident">Guard</span> {
<span class="comment">// An unprotected guard is just a `Guard` with its field `local` set to null.</span>
<span class="comment">// We make a newtype over `Guard` because `Guard` isn't `Sync`, so can't be directly stored in</span>
<span class="comment">// a `static`</span>
<span class="kw">struct</span> <span class="ident">GuardWrapper</span>(<span class="ident">Guard</span>);
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">GuardWrapper</span> {}
<span class="kw">static</span> <span class="ident">UNPROTECTED</span>: <span class="ident">GuardWrapper</span> <span class="op">=</span> <span class="ident">GuardWrapper</span>(<span class="ident">Guard</span> {
<span class="ident">local</span>: <span class="ident">core::ptr::null</span>(),
});
<span class="kw-2">&</span><span class="ident">UNPROTECTED</span>.<span class="number">0</span>
}
</pre></div>
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