github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sync/atomicptr/generic_atomicptr_unsafe.go (about)

     1  // Copyright 2019 The gVisor Authors.
     2  //
     3  // Use of this source code is governed by a BSD-style
     4  // license that can be found in the LICENSE file.
     5  
     6  // Package seqatomic doesn't exist. This file must be instantiated using the
     7  // go_template_instance rule in tools/go_generics/defs.bzl.
     8  package seqatomic
     9  
    10  import (
    11  	"sync/atomic"
    12  	"unsafe"
    13  )
    14  
    15  // Value is a required type parameter.
    16  type Value struct{}
    17  
    18  // An AtomicPtr is a pointer to a value of type Value that can be atomically
    19  // loaded and stored. The zero value of an AtomicPtr represents nil.
    20  //
    21  // Note that copying AtomicPtr by value performs a non-atomic read of the
    22  // stored pointer, which is unsafe if Store() can be called concurrently; in
    23  // this case, do `dst.Store(src.Load())` instead.
    24  //
    25  // +stateify savable
    26  type AtomicPtr struct {
    27  	ptr unsafe.Pointer `state:".(*Value)"`
    28  }
    29  
    30  func (p *AtomicPtr) savePtr() *Value {
    31  	return p.Load()
    32  }
    33  
    34  func (p *AtomicPtr) loadPtr(v *Value) {
    35  	p.Store(v)
    36  }
    37  
    38  // Load returns the value set by the most recent Store. It returns nil if there
    39  // has been no previous call to Store.
    40  func (p *AtomicPtr) Load() *Value {
    41  	return (*Value)(atomic.LoadPointer(&p.ptr))
    42  }
    43  
    44  // Store sets the value returned by Load to x.
    45  func (p *AtomicPtr) Store(x *Value) {
    46  	atomic.StorePointer(&p.ptr, (unsafe.Pointer)(x))
    47  }