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Source file src/sync/atomic/doc.go

Documentation: sync/atomic

     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  package atomic
    41  
    42  import (
    43  	"unsafe"
    44  )
    45  
    46  // BUG(rsc): On x86-32, the 64-bit functions use instructions unavailable before the Pentium MMX.
    47  //
    48  // On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core.
    49  //
    50  // On both ARM and x86-32, it is the caller's responsibility to arrange for 64-bit
    51  // alignment of 64-bit words accessed atomically. The first word in a
    52  // variable or in an allocated struct, array, or slice can be relied upon to be
    53  // 64-bit aligned.
    54  
    55  // SwapInt32 atomically stores new into *addr and returns the previous *addr value.
    56  func SwapInt32(addr *int32, new int32) (old int32)
    57  
    58  // SwapInt64 atomically stores new into *addr and returns the previous *addr value.
    59  func SwapInt64(addr *int64, new int64) (old int64)
    60  
    61  // SwapUint32 atomically stores new into *addr and returns the previous *addr value.
    62  func SwapUint32(addr *uint32, new uint32) (old uint32)
    63  
    64  // SwapUint64 atomically stores new into *addr and returns the previous *addr value.
    65  func SwapUint64(addr *uint64, new uint64) (old uint64)
    66  
    67  // SwapUintptr atomically stores new into *addr and returns the previous *addr value.
    68  func SwapUintptr(addr *uintptr, new uintptr) (old uintptr)
    69  
    70  // SwapPointer atomically stores new into *addr and returns the previous *addr value.
    71  func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)
    72  
    73  // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value.
    74  func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool)
    75  
    76  // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value.
    77  func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool)
    78  
    79  // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value.
    80  func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)
    81  
    82  // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value.
    83  func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool)
    84  
    85  // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value.
    86  func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool)
    87  
    88  // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value.
    89  func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool)
    90  
    91  // AddInt32 atomically adds delta to *addr and returns the new value.
    92  func AddInt32(addr *int32, delta int32) (new int32)
    93  
    94  // AddUint32 atomically adds delta to *addr and returns the new value.
    95  // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)).
    96  // In particular, to decrement x, do AddUint32(&x, ^uint32(0)).
    97  func AddUint32(addr *uint32, delta uint32) (new uint32)
    98  
    99  // AddInt64 atomically adds delta to *addr and returns the new value.
   100  func AddInt64(addr *int64, delta int64) (new int64)
   101  
   102  // AddUint64 atomically adds delta to *addr and returns the new value.
   103  // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)).
   104  // In particular, to decrement x, do AddUint64(&x, ^uint64(0)).
   105  func AddUint64(addr *uint64, delta uint64) (new uint64)
   106  
   107  // AddUintptr atomically adds delta to *addr and returns the new value.
   108  func AddUintptr(addr *uintptr, delta uintptr) (new uintptr)
   109  
   110  // LoadInt32 atomically loads *addr.
   111  func LoadInt32(addr *int32) (val int32)
   112  
   113  // LoadInt64 atomically loads *addr.
   114  func LoadInt64(addr *int64) (val int64)
   115  
   116  // LoadUint32 atomically loads *addr.
   117  func LoadUint32(addr *uint32) (val uint32)
   118  
   119  // LoadUint64 atomically loads *addr.
   120  func LoadUint64(addr *uint64) (val uint64)
   121  
   122  // LoadUintptr atomically loads *addr.
   123  func LoadUintptr(addr *uintptr) (val uintptr)
   124  
   125  // LoadPointer atomically loads *addr.
   126  func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer)
   127  
   128  // StoreInt32 atomically stores val into *addr.
   129  func StoreInt32(addr *int32, val int32)
   130  
   131  // StoreInt64 atomically stores val into *addr.
   132  func StoreInt64(addr *int64, val int64)
   133  
   134  // StoreUint32 atomically stores val into *addr.
   135  func StoreUint32(addr *uint32, val uint32)
   136  
   137  // StoreUint64 atomically stores val into *addr.
   138  func StoreUint64(addr *uint64, val uint64)
   139  
   140  // StoreUintptr atomically stores val into *addr.
   141  func StoreUintptr(addr *uintptr, val uintptr)
   142  
   143  // StorePointer atomically stores val into *addr.
   144  func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer)
   145  
   146  // Helper for ARM.  Linker will discard on other systems
   147  func panic64() {
   148  	panic("sync/atomic: broken 64-bit atomic operations (buggy QEMU)")
   149  }
   150  

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