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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	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 global
    52	// variable or in an allocated struct 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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