1/* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17#ifndef ANDROID_BASE_MACROS_H 18#define ANDROID_BASE_MACROS_H 19 20#include <stddef.h> // for size_t 21#include <unistd.h> // for TEMP_FAILURE_RETRY 22 23// bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't. 24#ifndef TEMP_FAILURE_RETRY 25#define TEMP_FAILURE_RETRY(exp) \ 26 ({ \ 27 decltype(exp) _rc; \ 28 do { \ 29 _rc = (exp); \ 30 } while (_rc == -1 && errno == EINTR); \ 31 _rc; \ 32 }) 33#endif 34 35// A macro to disallow the copy constructor and operator= functions 36// This must be placed in the private: declarations for a class. 37// 38// For disallowing only assign or copy, delete the relevant operator or 39// constructor, for example: 40// void operator=(const TypeName&) = delete; 41// Note, that most uses of DISALLOW_ASSIGN and DISALLOW_COPY are broken 42// semantically, one should either use disallow both or neither. Try to 43// avoid these in new code. 44#define DISALLOW_COPY_AND_ASSIGN(TypeName) \ 45 TypeName(const TypeName&) = delete; \ 46 void operator=(const TypeName&) = delete 47 48// A macro to disallow all the implicit constructors, namely the 49// default constructor, copy constructor and operator= functions. 50// 51// This should be used in the private: declarations for a class 52// that wants to prevent anyone from instantiating it. This is 53// especially useful for classes containing only static methods. 54#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \ 55 TypeName() = delete; \ 56 DISALLOW_COPY_AND_ASSIGN(TypeName) 57 58// The arraysize(arr) macro returns the # of elements in an array arr. 59// The expression is a compile-time constant, and therefore can be 60// used in defining new arrays, for example. If you use arraysize on 61// a pointer by mistake, you will get a compile-time error. 62// 63// One caveat is that arraysize() doesn't accept any array of an 64// anonymous type or a type defined inside a function. In these rare 65// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is 66// due to a limitation in C++'s template system. The limitation might 67// eventually be removed, but it hasn't happened yet. 68 69// This template function declaration is used in defining arraysize. 70// Note that the function doesn't need an implementation, as we only 71// use its type. 72template <typename T, size_t N> 73char(&ArraySizeHelper(T(&array)[N]))[N]; // NOLINT(readability/casting) 74 75#define arraysize(array) (sizeof(ArraySizeHelper(array))) 76 77// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize, 78// but can be used on anonymous types or types defined inside 79// functions. It's less safe than arraysize as it accepts some 80// (although not all) pointers. Therefore, you should use arraysize 81// whenever possible. 82// 83// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type 84// size_t. 85// 86// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error 87// 88// "warning: division by zero in ..." 89// 90// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer. 91// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays. 92// 93// The following comments are on the implementation details, and can 94// be ignored by the users. 95// 96// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in 97// the array) and sizeof(*(arr)) (the # of bytes in one array 98// element). If the former is divisible by the latter, perhaps arr is 99// indeed an array, in which case the division result is the # of 100// elements in the array. Otherwise, arr cannot possibly be an array, 101// and we generate a compiler error to prevent the code from 102// compiling. 103// 104// Since the size of bool is implementation-defined, we need to cast 105// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final 106// result has type size_t. 107// 108// This macro is not perfect as it wrongfully accepts certain 109// pointers, namely where the pointer size is divisible by the pointee 110// size. Since all our code has to go through a 32-bit compiler, 111// where a pointer is 4 bytes, this means all pointers to a type whose 112// size is 3 or greater than 4 will be (righteously) rejected. 113#define ARRAYSIZE_UNSAFE(a) \ 114 ((sizeof(a) / sizeof(*(a))) / \ 115 static_cast<size_t>(!(sizeof(a) % sizeof(*(a))))) 116 117// Changing this definition will cause you a lot of pain. A majority of 118// vendor code defines LIKELY and UNLIKELY this way, and includes 119// this header through an indirect path. 120#define LIKELY( exp ) (__builtin_expect( (exp) != 0, true )) 121#define UNLIKELY( exp ) (__builtin_expect( (exp) != 0, false )) 122 123#define WARN_UNUSED __attribute__((warn_unused_result)) 124 125// A deprecated function to call to create a false use of the parameter, for 126// example: 127// int foo(int x) { UNUSED(x); return 10; } 128// to avoid compiler warnings. Going forward we prefer ATTRIBUTE_UNUSED. 129template <typename... T> 130void UNUSED(const T&...) { 131} 132 133// An attribute to place on a parameter to a function, for example: 134// int foo(int x ATTRIBUTE_UNUSED) { return 10; } 135// to avoid compiler warnings. 136#define ATTRIBUTE_UNUSED __attribute__((__unused__)) 137 138// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through 139// between switch labels: 140// switch (x) { 141// case 40: 142// case 41: 143// if (truth_is_out_there) { 144// ++x; 145// FALLTHROUGH_INTENDED; // Use instead of/along with annotations in 146// // comments. 147// } else { 148// return x; 149// } 150// case 42: 151// ... 152// 153// As shown in the example above, the FALLTHROUGH_INTENDED macro should be 154// followed by a semicolon. It is designed to mimic control-flow statements 155// like 'break;', so it can be placed in most places where 'break;' can, but 156// only if there are no statements on the execution path between it and the 157// next switch label. 158// 159// When compiled with clang, the FALLTHROUGH_INTENDED macro is expanded to 160// [[clang::fallthrough]] attribute, which is analysed when performing switch 161// labels fall-through diagnostic ('-Wimplicit-fallthrough'). See clang 162// documentation on language extensions for details: 163// http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough 164// 165// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no 166// effect on diagnostics. 167// 168// In either case this macro has no effect on runtime behavior and performance 169// of code. 170#if defined(__clang__) && defined(__has_warning) 171#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough") 172#define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT 173#endif 174#endif 175 176#ifndef FALLTHROUGH_INTENDED 177#define FALLTHROUGH_INTENDED \ 178 do { \ 179 } while (0) 180#endif 181 182#endif // ANDROID_BASE_MACROS_H 183