gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/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  	"context"
    12  	"sync/atomic"
    13  	"unsafe"
    14  )
    15  
    16  // Value is a required type parameter.
    17  type Value struct{}
    18  
    19  // An AtomicPtr is a pointer to a value of type Value that can be atomically
    20  // loaded and stored. The zero value of an AtomicPtr represents nil.
    21  //
    22  // Note that copying AtomicPtr by value performs a non-atomic read of the
    23  // stored pointer, which is unsafe if Store() can be called concurrently; in
    24  // this case, do `dst.Store(src.Load())` instead.
    25  //
    26  // +stateify savable
    27  type AtomicPtr struct {
    28  	ptr unsafe.Pointer `state:".(*Value)"`
    29  }
    30  
    31  func (p *AtomicPtr) savePtr() *Value {
    32  	return p.Load()
    33  }
    34  
    35  func (p *AtomicPtr) loadPtr(_ context.Context, v *Value) {
    36  	p.Store(v)
    37  }
    38  
    39  // Load returns the value set by the most recent Store. It returns nil if there
    40  // has been no previous call to Store.
    41  //
    42  //go:nosplit
    43  func (p *AtomicPtr) Load() *Value {
    44  	return (*Value)(atomic.LoadPointer(&p.ptr))
    45  }
    46  
    47  // Store sets the value returned by Load to x.
    48  func (p *AtomicPtr) Store(x *Value) {
    49  	atomic.StorePointer(&p.ptr, (unsafe.Pointer)(x))
    50  }
    51  
    52  // Swap atomically stores `x` into *p and returns the previous *p value.
    53  func (p *AtomicPtr) Swap(x *Value) *Value {
    54  	return (*Value)(atomic.SwapPointer(&p.ptr, (unsafe.Pointer)(x)))
    55  }