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Diffstat (limited to 'base/include/base/macros.h')
| -rw-r--r-- | base/include/base/macros.h | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/base/include/base/macros.h b/base/include/base/macros.h new file mode 100644 index 0000000..b1ce7c6 --- /dev/null +++ b/base/include/base/macros.h @@ -0,0 +1,188 @@ +/* + * Copyright (C) 2015 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#ifndef UTILS_MACROS_H +#define UTILS_MACROS_H + +#include <stddef.h> // for size_t +#include <unistd.h> // for TEMP_FAILURE_RETRY + +// bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't. +#ifndef TEMP_FAILURE_RETRY +#define TEMP_FAILURE_RETRY(exp) \ + ({ \ + decltype(exp) _rc; \ + do { \ + _rc = (exp); \ + } while (_rc == -1 && errno == EINTR); \ + _rc; \ + }) +#endif + +// A macro to disallow the copy constructor and operator= functions +// This must be placed in the private: declarations for a class. +// +// For disallowing only assign or copy, delete the relevant operator or +// constructor, for example: +// void operator=(const TypeName&) = delete; +// Note, that most uses of DISALLOW_ASSIGN and DISALLOW_COPY are broken +// semantically, one should either use disallow both or neither. Try to +// avoid these in new code. +// +// When building with C++11 toolchains, just use the language support +// for explicitly deleted methods. +#if __cplusplus >= 201103L +#define DISALLOW_COPY_AND_ASSIGN(TypeName) \ + TypeName(const TypeName&) = delete; \ + void operator=(const TypeName&) = delete +#else +#define DISALLOW_COPY_AND_ASSIGN(TypeName) \ + TypeName(const TypeName&); \ + void operator=(const TypeName&) +#endif + +// A macro to disallow all the implicit constructors, namely the +// default constructor, copy constructor and operator= functions. +// +// This should be used in the private: declarations for a class +// that wants to prevent anyone from instantiating it. This is +// especially useful for classes containing only static methods. +#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \ + TypeName(); \ + DISALLOW_COPY_AND_ASSIGN(TypeName) + +// The arraysize(arr) macro returns the # of elements in an array arr. +// The expression is a compile-time constant, and therefore can be +// used in defining new arrays, for example. If you use arraysize on +// a pointer by mistake, you will get a compile-time error. +// +// One caveat is that arraysize() doesn't accept any array of an +// anonymous type or a type defined inside a function. In these rare +// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is +// due to a limitation in C++'s template system. The limitation might +// eventually be removed, but it hasn't happened yet. + +// This template function declaration is used in defining arraysize. +// Note that the function doesn't need an implementation, as we only +// use its type. +template <typename T, size_t N> +char(&ArraySizeHelper(T(&array)[N]))[N]; // NOLINT(readability/casting) + +#define arraysize(array) (sizeof(ArraySizeHelper(array))) + +// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize, +// but can be used on anonymous types or types defined inside +// functions. It's less safe than arraysize as it accepts some +// (although not all) pointers. Therefore, you should use arraysize +// whenever possible. +// +// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type +// size_t. +// +// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error +// +// "warning: division by zero in ..." +// +// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer. +// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays. +// +// The following comments are on the implementation details, and can +// be ignored by the users. +// +// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in +// the array) and sizeof(*(arr)) (the # of bytes in one array +// element). If the former is divisible by the latter, perhaps arr is +// indeed an array, in which case the division result is the # of +// elements in the array. Otherwise, arr cannot possibly be an array, +// and we generate a compiler error to prevent the code from +// compiling. +// +// Since the size of bool is implementation-defined, we need to cast +// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final +// result has type size_t. +// +// This macro is not perfect as it wrongfully accepts certain +// pointers, namely where the pointer size is divisible by the pointee +// size. Since all our code has to go through a 32-bit compiler, +// where a pointer is 4 bytes, this means all pointers to a type whose +// size is 3 or greater than 4 will be (righteously) rejected. +#define ARRAYSIZE_UNSAFE(a) \ + ((sizeof(a) / sizeof(*(a))) / \ + static_cast<size_t>(!(sizeof(a) % sizeof(*(a))))) + +#define LIKELY(x) __builtin_expect((x), true) +#define UNLIKELY(x) __builtin_expect((x), false) + +#define WARN_UNUSED __attribute__((warn_unused_result)) + +// A deprecated function to call to create a false use of the parameter, for +// example: +// int foo(int x) { UNUSED(x); return 10; } +// to avoid compiler warnings. Going forward we prefer ATTRIBUTE_UNUSED. +template <typename... T> +void UNUSED(const T&...) { +} + +// An attribute to place on a parameter to a function, for example: +// int foo(int x ATTRIBUTE_UNUSED) { return 10; } +// to avoid compiler warnings. +#define ATTRIBUTE_UNUSED __attribute__((__unused__)) + +// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through +// between switch labels: +// switch (x) { +// case 40: +// case 41: +// if (truth_is_out_there) { +// ++x; +// FALLTHROUGH_INTENDED; // Use instead of/along with annotations in +// // comments. +// } else { +// return x; +// } +// case 42: +// ... +// +// As shown in the example above, the FALLTHROUGH_INTENDED macro should be +// followed by a semicolon. It is designed to mimic control-flow statements +// like 'break;', so it can be placed in most places where 'break;' can, but +// only if there are no statements on the execution path between it and the +// next switch label. +// +// When compiled with clang in C++11 mode, the FALLTHROUGH_INTENDED macro is +// expanded to [[clang::fallthrough]] attribute, which is analysed when +// performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough'). +// See clang documentation on language extensions for details: +// http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough +// +// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no +// effect on diagnostics. +// +// In either case this macro has no effect on runtime behavior and performance +// of code. +#if defined(__clang__) && __cplusplus >= 201103L && defined(__has_warning) +#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough") +#define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT +#endif +#endif + +#ifndef FALLTHROUGH_INTENDED +#define FALLTHROUGH_INTENDED \ + do { \ + } while (0) +#endif + +#endif // UTILS_MACROS_H |