Fix races in the log module by using syncmap (#1421)
Mura Li
8 years ago
committed by
Bo-Yi Wu
parent
5d6b71fdbb
commit
93c25c9a35
@ -0,0 +1,27 @@ |
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Copyright (c) 2009 The Go Authors. All rights reserved. |
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Redistribution and use in source and binary forms, with or without |
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modification, are permitted provided that the following conditions are |
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met: |
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* Redistributions of source code must retain the above copyright |
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notice, this list of conditions and the following disclaimer. |
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* Redistributions in binary form must reproduce the above |
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copyright notice, this list of conditions and the following disclaimer |
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in the documentation and/or other materials provided with the |
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distribution. |
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* Neither the name of Google Inc. nor the names of its |
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contributors may be used to endorse or promote products derived from |
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this software without specific prior written permission. |
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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@ -0,0 +1,22 @@ |
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Additional IP Rights Grant (Patents) |
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"This implementation" means the copyrightable works distributed by |
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Google as part of the Go project. |
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Google hereby grants to You a perpetual, worldwide, non-exclusive, |
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transfer and otherwise run, modify and propagate the contents of this |
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implementation of Go. This grant does not include claims that would be |
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implementation. If you or your agent or exclusive licensee institute or |
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that this implementation of Go or any code incorporated within this |
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implementation of Go constitutes direct or contributory patent |
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infringement, or inducement of patent infringement, then any patent |
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rights granted to you under this License for this implementation of Go |
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shall terminate as of the date such litigation is filed. |
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@ -0,0 +1,372 @@ |
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// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package syncmap provides a concurrent map implementation.
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// It is a prototype for a proposed addition to the sync package
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// in the standard library.
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// (https://golang.org/issue/18177)
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package syncmap |
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import ( |
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"sync" |
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"sync/atomic" |
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"unsafe" |
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) |
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// Map is a concurrent map with amortized-constant-time loads, stores, and deletes.
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// It is safe for multiple goroutines to call a Map's methods concurrently.
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//
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// The zero Map is valid and empty.
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//
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// A Map must not be copied after first use.
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type Map struct { |
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mu sync.Mutex |
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// read contains the portion of the map's contents that are safe for
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// concurrent access (with or without mu held).
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//
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// The read field itself is always safe to load, but must only be stored with
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// mu held.
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//
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// Entries stored in read may be updated concurrently without mu, but updating
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// a previously-expunged entry requires that the entry be copied to the dirty
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// map and unexpunged with mu held.
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read atomic.Value // readOnly
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// dirty contains the portion of the map's contents that require mu to be
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// held. To ensure that the dirty map can be promoted to the read map quickly,
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// it also includes all of the non-expunged entries in the read map.
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//
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// Expunged entries are not stored in the dirty map. An expunged entry in the
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// clean map must be unexpunged and added to the dirty map before a new value
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// can be stored to it.
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//
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// If the dirty map is nil, the next write to the map will initialize it by
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// making a shallow copy of the clean map, omitting stale entries.
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dirty map[interface{}]*entry |
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// misses counts the number of loads since the read map was last updated that
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// needed to lock mu to determine whether the key was present.
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//
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// Once enough misses have occurred to cover the cost of copying the dirty
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// map, the dirty map will be promoted to the read map (in the unamended
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// state) and the next store to the map will make a new dirty copy.
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misses int |
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} |
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// readOnly is an immutable struct stored atomically in the Map.read field.
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type readOnly struct { |
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m map[interface{}]*entry |
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amended bool // true if the dirty map contains some key not in m.
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} |
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// expunged is an arbitrary pointer that marks entries which have been deleted
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// from the dirty map.
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var expunged = unsafe.Pointer(new(interface{})) |
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// An entry is a slot in the map corresponding to a particular key.
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type entry struct { |
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// p points to the interface{} value stored for the entry.
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//
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// If p == nil, the entry has been deleted and m.dirty == nil.
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//
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// If p == expunged, the entry has been deleted, m.dirty != nil, and the entry
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// is missing from m.dirty.
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//
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// Otherwise, the entry is valid and recorded in m.read.m[key] and, if m.dirty
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// != nil, in m.dirty[key].
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//
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// An entry can be deleted by atomic replacement with nil: when m.dirty is
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// next created, it will atomically replace nil with expunged and leave
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// m.dirty[key] unset.
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//
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// An entry's associated value can be updated by atomic replacement, provided
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// p != expunged. If p == expunged, an entry's associated value can be updated
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// only after first setting m.dirty[key] = e so that lookups using the dirty
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// map find the entry.
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p unsafe.Pointer // *interface{}
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} |
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func newEntry(i interface{}) *entry { |
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return &entry{p: unsafe.Pointer(&i)} |
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} |
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// Load returns the value stored in the map for a key, or nil if no
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// value is present.
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// The ok result indicates whether value was found in the map.
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func (m *Map) Load(key interface{}) (value interface{}, ok bool) { |
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read, _ := m.read.Load().(readOnly) |
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e, ok := read.m[key] |
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if !ok && read.amended { |
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m.mu.Lock() |
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// Avoid reporting a spurious miss if m.dirty got promoted while we were
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// blocked on m.mu. (If further loads of the same key will not miss, it's
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// not worth copying the dirty map for this key.)
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read, _ = m.read.Load().(readOnly) |
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e, ok = read.m[key] |
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if !ok && read.amended { |
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e, ok = m.dirty[key] |
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// Regardless of whether the entry was present, record a miss: this key
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// will take the slow path until the dirty map is promoted to the read
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// map.
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m.missLocked() |
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} |
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m.mu.Unlock() |
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} |
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if !ok { |
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return nil, false |
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} |
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return e.load() |
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} |
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func (e *entry) load() (value interface{}, ok bool) { |
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p := atomic.LoadPointer(&e.p) |
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if p == nil || p == expunged { |
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return nil, false |
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} |
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return *(*interface{})(p), true |
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} |
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// Store sets the value for a key.
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func (m *Map) Store(key, value interface{}) { |
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read, _ := m.read.Load().(readOnly) |
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if e, ok := read.m[key]; ok && e.tryStore(&value) { |
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return |
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} |
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m.mu.Lock() |
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read, _ = m.read.Load().(readOnly) |
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if e, ok := read.m[key]; ok { |
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if e.unexpungeLocked() { |
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// The entry was previously expunged, which implies that there is a
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// non-nil dirty map and this entry is not in it.
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m.dirty[key] = e |
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} |
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e.storeLocked(&value) |
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} else if e, ok := m.dirty[key]; ok { |
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e.storeLocked(&value) |
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} else { |
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if !read.amended { |
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// We're adding the first new key to the dirty map.
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// Make sure it is allocated and mark the read-only map as incomplete.
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m.dirtyLocked() |
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m.read.Store(readOnly{m: read.m, amended: true}) |
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} |
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m.dirty[key] = newEntry(value) |
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} |
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m.mu.Unlock() |
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} |
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// tryStore stores a value if the entry has not been expunged.
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//
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// If the entry is expunged, tryStore returns false and leaves the entry
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// unchanged.
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func (e *entry) tryStore(i *interface{}) bool { |
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p := atomic.LoadPointer(&e.p) |
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if p == expunged { |
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return false |
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} |
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for { |
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if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) { |
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return true |
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} |
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p = atomic.LoadPointer(&e.p) |
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if p == expunged { |
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return false |
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} |
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} |
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} |
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// unexpungeLocked ensures that the entry is not marked as expunged.
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//
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// If the entry was previously expunged, it must be added to the dirty map
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// before m.mu is unlocked.
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func (e *entry) unexpungeLocked() (wasExpunged bool) { |
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return atomic.CompareAndSwapPointer(&e.p, expunged, nil) |
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} |
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// storeLocked unconditionally stores a value to the entry.
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//
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// The entry must be known not to be expunged.
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func (e *entry) storeLocked(i *interface{}) { |
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atomic.StorePointer(&e.p, unsafe.Pointer(i)) |
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} |
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// LoadOrStore returns the existing value for the key if present.
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// Otherwise, it stores and returns the given value.
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// The loaded result is true if the value was loaded, false if stored.
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func (m *Map) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) { |
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// Avoid locking if it's a clean hit.
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read, _ := m.read.Load().(readOnly) |
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if e, ok := read.m[key]; ok { |
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actual, loaded, ok := e.tryLoadOrStore(value) |
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if ok { |
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return actual, loaded |
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} |
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} |
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m.mu.Lock() |
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read, _ = m.read.Load().(readOnly) |
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if e, ok := read.m[key]; ok { |
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if e.unexpungeLocked() { |
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m.dirty[key] = e |
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} |
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actual, loaded, _ = e.tryLoadOrStore(value) |
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} else if e, ok := m.dirty[key]; ok { |
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actual, loaded, _ = e.tryLoadOrStore(value) |
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m.missLocked() |
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} else { |
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if !read.amended { |
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// We're adding the first new key to the dirty map.
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// Make sure it is allocated and mark the read-only map as incomplete.
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m.dirtyLocked() |
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m.read.Store(readOnly{m: read.m, amended: true}) |
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} |
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m.dirty[key] = newEntry(value) |
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actual, loaded = value, false |
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} |
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m.mu.Unlock() |
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return actual, loaded |
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} |
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// tryLoadOrStore atomically loads or stores a value if the entry is not
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// expunged.
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//
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// If the entry is expunged, tryLoadOrStore leaves the entry unchanged and
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// returns with ok==false.
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func (e *entry) tryLoadOrStore(i interface{}) (actual interface{}, loaded, ok bool) { |
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p := atomic.LoadPointer(&e.p) |
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if p == expunged { |
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return nil, false, false |
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} |
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if p != nil { |
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return *(*interface{})(p), true, true |
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} |
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// Copy the interface after the first load to make this method more amenable
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// to escape analysis: if we hit the "load" path or the entry is expunged, we
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// shouldn't bother heap-allocating.
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ic := i |
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for { |
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if atomic.CompareAndSwapPointer(&e.p, nil, unsafe.Pointer(&ic)) { |
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return i, false, true |
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} |
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p = atomic.LoadPointer(&e.p) |
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if p == expunged { |
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return nil, false, false |
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} |
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if p != nil { |
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return *(*interface{})(p), true, true |
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} |
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} |
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} |
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// Delete deletes the value for a key.
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func (m *Map) Delete(key interface{}) { |
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read, _ := m.read.Load().(readOnly) |
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e, ok := read.m[key] |
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if !ok && read.amended { |
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m.mu.Lock() |
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read, _ = m.read.Load().(readOnly) |
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e, ok = read.m[key] |
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if !ok && read.amended { |
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delete(m.dirty, key) |
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} |
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m.mu.Unlock() |
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} |
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if ok { |
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e.delete() |
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} |
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} |
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func (e *entry) delete() (hadValue bool) { |
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for { |
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p := atomic.LoadPointer(&e.p) |
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if p == nil || p == expunged { |
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return false |
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} |
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if atomic.CompareAndSwapPointer(&e.p, p, nil) { |
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return true |
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} |
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} |
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} |
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// Range calls f sequentially for each key and value present in the map.
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// If f returns false, range stops the iteration.
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//
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// Range does not necessarily correspond to any consistent snapshot of the Map's
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// contents: no key will be visited more than once, but if the value for any key
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// is stored or deleted concurrently, Range may reflect any mapping for that key
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// from any point during the Range call.
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//
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// Range may be O(N) with the number of elements in the map even if f returns
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// false after a constant number of calls.
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func (m *Map) Range(f func(key, value interface{}) bool) { |
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// We need to be able to iterate over all of the keys that were already
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// present at the start of the call to Range.
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// If read.amended is false, then read.m satisfies that property without
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// requiring us to hold m.mu for a long time.
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read, _ := m.read.Load().(readOnly) |
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if read.amended { |
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// m.dirty contains keys not in read.m. Fortunately, Range is already O(N)
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// (assuming the caller does not break out early), so a call to Range
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// amortizes an entire copy of the map: we can promote the dirty copy
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// immediately!
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m.mu.Lock() |
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read, _ = m.read.Load().(readOnly) |
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if read.amended { |
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read = readOnly{m: m.dirty} |
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m.read.Store(read) |
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m.dirty = nil |
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m.misses = 0 |
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} |
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m.mu.Unlock() |
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} |
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for k, e := range read.m { |
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v, ok := e.load() |
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if !ok { |
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continue |
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} |
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if !f(k, v) { |
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break |
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} |
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} |
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} |
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func (m *Map) missLocked() { |
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m.misses++ |
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if m.misses < len(m.dirty) { |
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return |
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} |
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m.read.Store(readOnly{m: m.dirty}) |
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m.dirty = nil |
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m.misses = 0 |
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} |
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func (m *Map) dirtyLocked() { |
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if m.dirty != nil { |
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return |
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} |
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read, _ := m.read.Load().(readOnly) |
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m.dirty = make(map[interface{}]*entry, len(read.m)) |
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for k, e := range read.m { |
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if !e.tryExpungeLocked() { |
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m.dirty[k] = e |
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} |
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} |
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} |
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func (e *entry) tryExpungeLocked() (isExpunged bool) { |
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p := atomic.LoadPointer(&e.p) |
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for p == nil { |
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if atomic.CompareAndSwapPointer(&e.p, nil, expunged) { |
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return true |
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} |
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p = atomic.LoadPointer(&e.p) |
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} |
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return p == expunged |
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} |
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Reference in new issue