Introduce mongo/platform/compiler.h.

Get rid of most uses of __attribute__ and __declspec outside of the
platform/compiler headers.

1 files changed, 71 insertions, 0 deletions

diff --git a/src/mongo/platform/compiler_gcc.h b/src/mongo/platform/compiler_gcc.h
new file mode 100644
index 00000000000..878d2ce7465
--- /dev/null
+++ b/src/mongo/platform/compiler_gcc.h
@@ -0,0 +1,71 @@
+// @file mongo/platform/compiler_gcc.h
+
+/*
+ * Copyright 2012 10gen Inc.
+ *
+ * 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.
+ */
+
+#pragma once
+
+/**
+ * Compiler-specific implementations for gcc.
+ */
+
+/**
+ * Use this to decorate the declaration of functions that will not return.
+ *
+ * Correct:
+ *    MONGO_COMPILER_NORETURN void myAbortFunction();
+ */
+#define MONGO_COMPILER_NORETURN __attribute__((__noreturn__))
+
+/**
+ * Use this to decorate unused variable declarations.
+ */
+#define MONGO_COMPILER_VARIABLE_UNUSED __attribute__((__unused__))
+
+/**
+ * Use this on a type declaration to specify its minimum alignment.
+ *
+ * Alignments should probably always be powers of two.  Also, note that most allocators will not be
+ * able to guarantee better than 16- or 32-byte alignment.
+ *
+ * Correct:
+ *    class MONGO_COMPILER_ALIGN_TYPE(16) MyClass {...};
+ *
+ * Incorrect:
+ *    MONGO_COMPILER_ALIGN_TYPE(16) class MyClass {...};
+ *    class MyClass{...} MONGO_COMPILER_ALIGN_TYPE(16);
+ */
+#define MONGO_COMPILER_ALIGN_TYPE(ALIGNMENT) __attribute__(( __aligned__(ALIGNMENT) ))
+
+/**
+ * Use this on a global variable or structure field declaration to specify that it must be allocated
+ * at a location that is aligned to a multiple of "ALIGNMENT" bytes.
+ *
+ * Note that most allocators will not allow heap allocated alignments that are better than 16- or
+ * 32-byte aligned.  Stack allocators may only guarantee up to the natural word length worth of
+ * alignment.
+ *
+ * Correct:
+ *    class MyClass {
+ *        MONGO_COMPILER_ALIGN_VARIABLE(8) char a;
+ *    };
+ *
+ *    MONGO_COMPILER_ALIGN_VARIABLE(8) class MyClass {...} singletonInstance;
+ *
+ * Incorrect:
+ *    int MONGO_COMPILER_ALIGN_VARIABLE(16) a, b;
+ */
+#define MONGO_COMPILER_ALIGN_VARIABLE(ALIGNMENT) __attribute__(( __aligned__(ALIGNMENT) ))