Source file src/sync/atomic/doc.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package atomic provides low-level atomic memory primitives
     6  // useful for implementing synchronization algorithms.
     7  //
     8  // These functions require great care to be used correctly.
     9  // Except for special, low-level applications, synchronization is better
    10  // done with channels or the facilities of the sync package.
    11  // Share memory by communicating;
    12  // don't communicate by sharing memory.
    13  //
    14  // The swap operation, implemented by the SwapT functions, is the atomic
    15  // equivalent of:
    16  //
    17  //	old = *addr
    18  //	*addr = new
    19  //	return old
    20  //
    21  // The compare-and-swap operation, implemented by the CompareAndSwapT
    22  // functions, is the atomic equivalent of:
    23  //
    24  //	if *addr == old {
    25  //		*addr = new
    26  //		return true
    27  //	}
    28  //	return false
    29  //
    30  // The add operation, implemented by the AddT functions, is the atomic
    31  // equivalent of:
    32  //
    33  //	*addr += delta
    34  //	return *addr
    35  //
    36  // The load and store operations, implemented by the LoadT and StoreT
    37  // functions, are the atomic equivalents of "return *addr" and
    38  // "*addr = val".
    39  //
    40  // In the terminology of the Go memory model, if the effect of
    41  // an atomic operation A is observed by atomic operation B,
    42  // then A “synchronizes before” B.
    43  // Additionally, all the atomic operations executed in a program
    44  // behave as though executed in some sequentially consistent order.
    45  // This definition provides the same semantics as
    46  // C++'s sequentially consistent atomics and Java's volatile variables.
    47  package atomic
    48  
    49  import (
    50  	"unsafe"
    51  )
    52  
    53  // BUG(rsc): On 386, the 64-bit functions use instructions unavailable before the Pentium MMX.
    54  //
    55  // On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core.
    56  //
    57  // On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
    58  // for 64-bit alignment of 64-bit words accessed atomically via the primitive
    59  // atomic functions (types Int64 and Uint64 are automatically aligned).
    60  // The first word in an allocated struct, array, or slice; in a global
    61  // variable; or in a local variable (because the subject of all atomic operations
    62  // will escape to the heap) can be relied upon to be 64-bit aligned.
    63  
    64  // SwapInt32 atomically stores new into *addr and returns the previous *addr value.
    65  func SwapInt32(addr *int32, new int32) (old int32)
    66  
    67  // SwapInt64 atomically stores new into *addr and returns the previous *addr value.
    68  func SwapInt64(addr *int64, new int64) (old int64)
    69  
    70  // SwapUint32 atomically stores new into *addr and returns the previous *addr value.
    71  func SwapUint32(addr *uint32, new uint32) (old uint32)
    72  
    73  // SwapUint64 atomically stores new into *addr and returns the previous *addr value.
    74  func SwapUint64(addr *uint64, new uint64) (old uint64)
    75  
    76  // SwapUintptr atomically stores new into *addr and returns the previous *addr value.
    77  func SwapUintptr(addr *uintptr, new uintptr) (old uintptr)
    78  
    79  // SwapPointer atomically stores new into *addr and returns the previous *addr value.
    80  func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)
    81  
    82  // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value.
    83  func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool)
    84  
    85  // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value.
    86  func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool)
    87  
    88  // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value.
    89  func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)
    90  
    91  // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value.
    92  func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool)
    93  
    94  // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value.
    95  func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool)
    96  
    97  // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value.
    98  func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool)
    99  
   100  // AddInt32 atomically adds delta to *addr and returns the new value.
   101  func AddInt32(addr *int32, delta int32) (new int32)
   102  
   103  // AddUint32 atomically adds delta to *addr and returns the new value.
   104  // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)).
   105  // In particular, to decrement x, do AddUint32(&x, ^uint32(0)).
   106  func AddUint32(addr *uint32, delta uint32) (new uint32)
   107  
   108  // AddInt64 atomically adds delta to *addr and returns the new value.
   109  func AddInt64(addr *int64, delta int64) (new int64)
   110  
   111  // AddUint64 atomically adds delta to *addr and returns the new value.
   112  // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)).
   113  // In particular, to decrement x, do AddUint64(&x, ^uint64(0)).
   114  func AddUint64(addr *uint64, delta uint64) (new uint64)
   115  
   116  // AddUintptr atomically adds delta to *addr and returns the new value.
   117  func AddUintptr(addr *uintptr, delta uintptr) (new uintptr)
   118  
   119  // LoadInt32 atomically loads *addr.
   120  func LoadInt32(addr *int32) (val int32)
   121  
   122  // LoadInt64 atomically loads *addr.
   123  func LoadInt64(addr *int64) (val int64)
   124  
   125  // LoadUint32 atomically loads *addr.
   126  func LoadUint32(addr *uint32) (val uint32)
   127  
   128  // LoadUint64 atomically loads *addr.
   129  func LoadUint64(addr *uint64) (val uint64)
   130  
   131  // LoadUintptr atomically loads *addr.
   132  func LoadUintptr(addr *uintptr) (val uintptr)
   133  
   134  // LoadPointer atomically loads *addr.
   135  func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer)
   136  
   137  // StoreInt32 atomically stores val into *addr.
   138  func StoreInt32(addr *int32, val int32)
   139  
   140  // StoreInt64 atomically stores val into *addr.
   141  func StoreInt64(addr *int64, val int64)
   142  
   143  // StoreUint32 atomically stores val into *addr.
   144  func StoreUint32(addr *uint32, val uint32)
   145  
   146  // StoreUint64 atomically stores val into *addr.
   147  func StoreUint64(addr *uint64, val uint64)
   148  
   149  // StoreUintptr atomically stores val into *addr.
   150  func StoreUintptr(addr *uintptr, val uintptr)
   151  
   152  // StorePointer atomically stores val into *addr.
   153  func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer)
   154  

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