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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  // 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  //
    48  // [the Go memory model]: https://go.dev/ref/mem
    49  package atomic
    50  
    51  import (
    52  	"unsafe"
    53  )
    54  
    55  // BUG(rsc): On 386, the 64-bit functions use instructions unavailable before the Pentium MMX.
    56  //
    57  // On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core.
    58  //
    59  // On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
    60  // for 64-bit alignment of 64-bit words accessed atomically via the primitive
    61  // atomic functions (types [Int64] and [Uint64] are automatically aligned).
    62  // The first word in an allocated struct, array, or slice; in a global
    63  // variable; or in a local variable (because the subject of all atomic operations
    64  // will escape to the heap) can be relied upon to be 64-bit aligned.
    65  
    66  // SwapInt32 atomically stores new into *addr and returns the previous *addr value.
    67  // Consider using the more ergonomic and less error-prone [Int32.Swap] instead.
    68  func SwapInt32(addr *int32, new int32) (old int32)
    69  
    70  // SwapInt64 atomically stores new into *addr and returns the previous *addr value.
    71  // Consider using the more ergonomic and less error-prone [Int64.Swap] instead
    72  // (particularly if you target 32-bit platforms; see the bugs section).
    73  func SwapInt64(addr *int64, new int64) (old int64)
    74  
    75  // SwapUint32 atomically stores new into *addr and returns the previous *addr value.
    76  // Consider using the more ergonomic and less error-prone [Uint32.Swap] instead.
    77  func SwapUint32(addr *uint32, new uint32) (old uint32)
    78  
    79  // SwapUint64 atomically stores new into *addr and returns the previous *addr value.
    80  // Consider using the more ergonomic and less error-prone [Uint64.Swap] instead
    81  // (particularly if you target 32-bit platforms; see the bugs section).
    82  func SwapUint64(addr *uint64, new uint64) (old uint64)
    83  
    84  // SwapUintptr atomically stores new into *addr and returns the previous *addr value.
    85  // Consider using the more ergonomic and less error-prone [Uintptr.Swap] instead.
    86  func SwapUintptr(addr *uintptr, new uintptr) (old uintptr)
    87  
    88  // SwapPointer atomically stores new into *addr and returns the previous *addr value.
    89  // Consider using the more ergonomic and less error-prone [Pointer.Swap] instead.
    90  func SwapPointer(addr *unsafe.Pointer, new unsafe.Pointer) (old unsafe.Pointer)
    91  
    92  // CompareAndSwapInt32 executes the compare-and-swap operation for an int32 value.
    93  // Consider using the more ergonomic and less error-prone [Int32.CompareAndSwap] instead.
    94  func CompareAndSwapInt32(addr *int32, old, new int32) (swapped bool)
    95  
    96  // CompareAndSwapInt64 executes the compare-and-swap operation for an int64 value.
    97  // Consider using the more ergonomic and less error-prone [Int64.CompareAndSwap] instead
    98  // (particularly if you target 32-bit platforms; see the bugs section).
    99  func CompareAndSwapInt64(addr *int64, old, new int64) (swapped bool)
   100  
   101  // CompareAndSwapUint32 executes the compare-and-swap operation for a uint32 value.
   102  // Consider using the more ergonomic and less error-prone [Uint32.CompareAndSwap] instead.
   103  func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)
   104  
   105  // CompareAndSwapUint64 executes the compare-and-swap operation for a uint64 value.
   106  // Consider using the more ergonomic and less error-prone [Uint64.CompareAndSwap] instead
   107  // (particularly if you target 32-bit platforms; see the bugs section).
   108  func CompareAndSwapUint64(addr *uint64, old, new uint64) (swapped bool)
   109  
   110  // CompareAndSwapUintptr executes the compare-and-swap operation for a uintptr value.
   111  // Consider using the more ergonomic and less error-prone [Uintptr.CompareAndSwap] instead.
   112  func CompareAndSwapUintptr(addr *uintptr, old, new uintptr) (swapped bool)
   113  
   114  // CompareAndSwapPointer executes the compare-and-swap operation for a unsafe.Pointer value.
   115  // Consider using the more ergonomic and less error-prone [Pointer.CompareAndSwap] instead.
   116  func CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) (swapped bool)
   117  
   118  // AddInt32 atomically adds delta to *addr and returns the new value.
   119  // Consider using the more ergonomic and less error-prone [Int32.Add] instead.
   120  func AddInt32(addr *int32, delta int32) (new int32)
   121  
   122  // AddUint32 atomically adds delta to *addr and returns the new value.
   123  // To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)).
   124  // In particular, to decrement x, do AddUint32(&x, ^uint32(0)).
   125  // Consider using the more ergonomic and less error-prone [Uint32.Add] instead.
   126  func AddUint32(addr *uint32, delta uint32) (new uint32)
   127  
   128  // AddInt64 atomically adds delta to *addr and returns the new value.
   129  // Consider using the more ergonomic and less error-prone [Int64.Add] instead
   130  // (particularly if you target 32-bit platforms; see the bugs section).
   131  func AddInt64(addr *int64, delta int64) (new int64)
   132  
   133  // AddUint64 atomically adds delta to *addr and returns the new value.
   134  // To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)).
   135  // In particular, to decrement x, do AddUint64(&x, ^uint64(0)).
   136  // Consider using the more ergonomic and less error-prone [Uint64.Add] instead
   137  // (particularly if you target 32-bit platforms; see the bugs section).
   138  func AddUint64(addr *uint64, delta uint64) (new uint64)
   139  
   140  // AddUintptr atomically adds delta to *addr and returns the new value.
   141  // Consider using the more ergonomic and less error-prone [Uintptr.Add] instead.
   142  func AddUintptr(addr *uintptr, delta uintptr) (new uintptr)
   143  
   144  // AndInt32 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask
   145  // and returns the old value.
   146  // Consider using the more ergonomic and less error-prone [Int32.And] instead.
   147  func AndInt32(addr *int32, mask int32) (old int32)
   148  
   149  // AndUint32 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask
   150  // and returns the old value.
   151  // Consider using the more ergonomic and less error-prone [Uint32.And] instead.
   152  func AndUint32(addr *uint32, mask uint32) (old uint32)
   153  
   154  // AndInt64 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask
   155  // and returns the old value.
   156  // Consider using the more ergonomic and less error-prone [Int64.And] instead.
   157  func AndInt64(addr *int64, mask int64) (old int64)
   158  
   159  // AndUint64 atomically performs a bitwise AND operation on *addr using the bitmask provided as mask
   160  // and returns the old.
   161  // Consider using the more ergonomic and less error-prone [Uint64.And] instead.
   162  func AndUint64(addr *uint64, mask uint64) (old uint64)
   163  
   164  // AndUintptr atomically performs a bitwise AND operation on *addr using the bitmask provided as mask
   165  // and returns the old value.
   166  // Consider using the more ergonomic and less error-prone [Uintptr.And] instead.
   167  func AndUintptr(addr *uintptr, mask uintptr) (old uintptr)
   168  
   169  // OrInt32 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask
   170  // and returns the old value.
   171  // Consider using the more ergonomic and less error-prone [Int32.Or] instead.
   172  func OrInt32(addr *int32, mask int32) (old int32)
   173  
   174  // OrUint32 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask
   175  // and returns the old value.
   176  // Consider using the more ergonomic and less error-prone [Uint32.Or] instead.
   177  func OrUint32(addr *uint32, mask uint32) (old uint32)
   178  
   179  // OrInt64 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask
   180  // and returns the old value.
   181  // Consider using the more ergonomic and less error-prone [Int64.Or] instead.
   182  func OrInt64(addr *int64, mask int64) (old int64)
   183  
   184  // OrUint64 atomically performs a bitwise OR operation on *addr using the bitmask provided as mask
   185  // and returns the old value.
   186  // Consider using the more ergonomic and less error-prone [Uint64.Or] instead.
   187  func OrUint64(addr *uint64, mask uint64) (old uint64)
   188  
   189  // OrUintptr atomically performs a bitwise OR operation on *addr using the bitmask provided as mask
   190  // and returns the old value.
   191  // Consider using the more ergonomic and less error-prone [Uintptr.Or] instead.
   192  func OrUintptr(addr *uintptr, mask uintptr) (old uintptr)
   193  
   194  // LoadInt32 atomically loads *addr.
   195  // Consider using the more ergonomic and less error-prone [Int32.Load] instead.
   196  func LoadInt32(addr *int32) (val int32)
   197  
   198  // LoadInt64 atomically loads *addr.
   199  // Consider using the more ergonomic and less error-prone [Int64.Load] instead
   200  // (particularly if you target 32-bit platforms; see the bugs section).
   201  func LoadInt64(addr *int64) (val int64)
   202  
   203  // LoadUint32 atomically loads *addr.
   204  // Consider using the more ergonomic and less error-prone [Uint32.Load] instead.
   205  func LoadUint32(addr *uint32) (val uint32)
   206  
   207  // LoadUint64 atomically loads *addr.
   208  // Consider using the more ergonomic and less error-prone [Uint64.Load] instead
   209  // (particularly if you target 32-bit platforms; see the bugs section).
   210  func LoadUint64(addr *uint64) (val uint64)
   211  
   212  // LoadUintptr atomically loads *addr.
   213  // Consider using the more ergonomic and less error-prone [Uintptr.Load] instead.
   214  func LoadUintptr(addr *uintptr) (val uintptr)
   215  
   216  // LoadPointer atomically loads *addr.
   217  // Consider using the more ergonomic and less error-prone [Pointer.Load] instead.
   218  func LoadPointer(addr *unsafe.Pointer) (val unsafe.Pointer)
   219  
   220  // StoreInt32 atomically stores val into *addr.
   221  // Consider using the more ergonomic and less error-prone [Int32.Store] instead.
   222  func StoreInt32(addr *int32, val int32)
   223  
   224  // StoreInt64 atomically stores val into *addr.
   225  // Consider using the more ergonomic and less error-prone [Int64.Store] instead
   226  // (particularly if you target 32-bit platforms; see the bugs section).
   227  func StoreInt64(addr *int64, val int64)
   228  
   229  // StoreUint32 atomically stores val into *addr.
   230  // Consider using the more ergonomic and less error-prone [Uint32.Store] instead.
   231  func StoreUint32(addr *uint32, val uint32)
   232  
   233  // StoreUint64 atomically stores val into *addr.
   234  // Consider using the more ergonomic and less error-prone [Uint64.Store] instead
   235  // (particularly if you target 32-bit platforms; see the bugs section).
   236  func StoreUint64(addr *uint64, val uint64)
   237  
   238  // StoreUintptr atomically stores val into *addr.
   239  // Consider using the more ergonomic and less error-prone [Uintptr.Store] instead.
   240  func StoreUintptr(addr *uintptr, val uintptr)
   241  
   242  // StorePointer atomically stores val into *addr.
   243  // Consider using the more ergonomic and less error-prone [Pointer.Store] instead.
   244  func StorePointer(addr *unsafe.Pointer, val unsafe.Pointer)
   245  

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