mirror of
https://github.com/autc04/Retro68.git
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87 lines
2.4 KiB
Go
87 lines
2.4 KiB
Go
// Copyright 2014 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 atomic
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import (
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"unsafe"
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)
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// A Value provides an atomic load and store of a consistently typed value.
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// The zero value for a Value returns nil from Load.
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// Once Store has been called, a Value must not be copied.
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//
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// A Value must not be copied after first use.
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type Value struct {
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v interface{}
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}
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// ifaceWords is interface{} internal representation.
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type ifaceWords struct {
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typ unsafe.Pointer
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data unsafe.Pointer
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}
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// Load returns the value set by the most recent Store.
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// It returns nil if there has been no call to Store for this Value.
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func (v *Value) Load() (x interface{}) {
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vp := (*ifaceWords)(unsafe.Pointer(v))
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typ := LoadPointer(&vp.typ)
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if typ == nil || uintptr(typ) == ^uintptr(0) {
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// First store not yet completed.
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return nil
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}
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data := LoadPointer(&vp.data)
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xp := (*ifaceWords)(unsafe.Pointer(&x))
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xp.typ = typ
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xp.data = data
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return
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}
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// Store sets the value of the Value to x.
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// All calls to Store for a given Value must use values of the same concrete type.
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// Store of an inconsistent type panics, as does Store(nil).
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func (v *Value) Store(x interface{}) {
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if x == nil {
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panic("sync/atomic: store of nil value into Value")
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}
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vp := (*ifaceWords)(unsafe.Pointer(v))
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xp := (*ifaceWords)(unsafe.Pointer(&x))
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for {
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typ := LoadPointer(&vp.typ)
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if typ == nil {
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// Attempt to start first store.
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// Disable preemption so that other goroutines can use
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// active spin wait to wait for completion; and so that
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// GC does not see the fake type accidentally.
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runtime_procPin()
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if !CompareAndSwapPointer(&vp.typ, nil, unsafe.Pointer(^uintptr(0))) {
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runtime_procUnpin()
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continue
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}
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// Complete first store.
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StorePointer(&vp.data, xp.data)
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StorePointer(&vp.typ, xp.typ)
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runtime_procUnpin()
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return
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}
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if uintptr(typ) == ^uintptr(0) {
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// First store in progress. Wait.
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// Since we disable preemption around the first store,
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// we can wait with active spinning.
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continue
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}
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// First store completed. Check type and overwrite data.
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if typ != xp.typ {
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panic("sync/atomic: store of inconsistently typed value into Value")
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}
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StorePointer(&vp.data, xp.data)
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return
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}
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}
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// Disable/enable preemption, implemented in runtime.
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func runtime_procPin()
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func runtime_procUnpin()
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