Add commonly used C++ macros to libbase.

Change-Id: I74f5dbfc4d99f7e78212a72540e538c1a737e224

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 000000000..b1ce7c6ba
--- /dev/null
+++ b/base/include/base/macros.h
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+/*
+ * 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