SERVER-6018 Use gcc __sync primitives if they are available and useable

SConstruct

@@ -1441,17 +1441,52 @@ def doConfigure(myenv):
                 return 0;
             }
             """
-            context.Message('Checking for gcc atomic builtins... ')
+            context.Message('Checking for gcc __atomic builtins... ')
             ret = context.TryLink(textwrap.dedent(test_body), '.cpp')
             context.Result(ret)
             return ret
+
+        def CheckGCCSyncBuiltins(context):
+            test_body = """
+            int main(int argc, char **argv) {
+                int a = 0;
+                return __sync_fetch_and_add(&a, 1);
+            }
+
+            //
+            // Figure out if we are using gcc older than 4.2 to target 32-bit x86. If so, error out
+            // even if we were able to compile the __sync statement, due to
+            // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40693
+            //
+            #if defined(__i386__)
+            #if !defined(__clang__)
+            #if defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ < 2)
+            #error "Refusing to use __sync in 32-bit mode with gcc older than 4.2"
+            #endif
+            #endif
+            #endif
+            """
+
+            context.Message('Checking for useable __sync builtins... ')
+            ret = context.TryLink(textwrap.dedent(test_body), '.cpp')
+            context.Result(ret)
+            return ret
+
         conf = Configure(myenv, help=False, custom_tests = {
             'CheckGCCAtomicBuiltins': CheckGCCAtomicBuiltins,
+            'CheckGCCSyncBuiltins': CheckGCCSyncBuiltins,
         })
-        haveGCCAtomicBuiltins = conf.CheckGCCAtomicBuiltins()
-        conf.Finish()
-        if haveGCCAtomicBuiltins:
-            conf.env.Append(CPPDEFINES=["HAVE_GCC_ATOMIC_BUILTINS"])
+
+        # Prefer the __atomic builtins. If we don't have those, try for __sync. Otherwise
+        # atomic_intrinsics.h will try to fall back to the hand-rolled assembly implementations
+        # in atomic_intrinsics_gcc_intel for x86 platforms.
+        if conf.CheckGCCAtomicBuiltins():
+            conf.env.Append(CPPDEFINES=["MONGO_HAVE_GCC_ATOMIC_BUILTINS"])
+        else:
+            if conf.CheckGCCSyncBuiltins():
+                conf.env.Append(CPPDEFINES=["MONGO_HAVE_GCC_SYNC_BUILTINS"])
+
+        myenv = conf.Finish()
 
     conf = Configure(myenv)
     libdeps.setup_conftests(conf)

src/mongo/platform/atomic_intrinsics.h

@@ -54,14 +54,12 @@
 
 #if defined(_WIN32)
 #include "mongo/platform/atomic_intrinsics_win32.h"
-#elif defined(__GNUC__)
-#if defined(HAVE_GCC_ATOMIC_BUILTINS)
-#include "mongo/platform/atomic_intrinsics_gcc_generic.h"
+#elif defined(MONGO_HAVE_GCC_ATOMIC_BUILTINS)
+#include "mongo/platform/atomic_intrinsics_gcc_atomic.h"
+#elif defined(MONGO_HAVE_GCC_SYNC_BUILTINS)
+#include "mongo/platform/atomic_intrinsics_gcc_sync.h"
 #elif defined(__i386__) || defined(__x86_64__)
 #include "mongo/platform/atomic_intrinsics_gcc_intel.h"
 #else
-#error "Unsupported platform: no gcc atomic builtins or port available"
-#endif
-#else
 #error "Unsupported os/compiler family"
 #endif

src/mongo/platform/atomic_intrinsics_gcc_atomic.h

@@ -32,8 +32,6 @@
 
 #pragma once
 
-#include <boost/utility.hpp>
-
 namespace mongo {
 
     /**

src/mongo/platform/atomic_intrinsics_gcc_sync.h

@@ -0,0 +1,110 @@
+/*    Copyright 2014 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.
+ */
+
+/**
+ * Implementation of the AtomicIntrinsics<T>::* operations for systems on any
+ * architecture using a GCC 4.1+ compatible compiler toolchain.
+ */
+
+#pragma once
+
+#include <boost/utility.hpp>
+
+namespace mongo {
+
+    /**
+     * Instantiation of AtomicIntrinsics<> for all word types T.
+     */
+    template <typename T, typename IsTLarge=void>
+    class AtomicIntrinsics {
+    public:
+
+        static T compareAndSwap(volatile T* dest, T expected, T newValue) {
+            return __sync_val_compare_and_swap(dest, expected, newValue);
+        }
+
+        static T swap(volatile T* dest, T newValue) {
+            T currentValue = *dest;
+            while (true) {
+                const T result = compareAndSwap(dest, currentValue, newValue);
+                if (result == currentValue)
+                    return result;
+                currentValue = result;
+            }
+        }
+
+        static T load(volatile const T* value) {
+            __sync_synchronize();
+            T result = *value;
+            __sync_synchronize();
+            return result;
+        }
+
+        static T loadRelaxed(volatile const T* value) {
+            asm volatile("" ::: "memory");
+            return *value;
+        }
+
+        static void store(volatile T* dest, T newValue) {
+            __sync_synchronize();
+            *dest = newValue;
+            __sync_synchronize();
+        }
+
+        static T fetchAndAdd(volatile T* dest, T increment) {
+            return __sync_fetch_and_add(dest, increment);
+        }
+
+    private:
+        AtomicIntrinsics();
+        ~AtomicIntrinsics();
+    };
+
+    template <typename T>
+    class AtomicIntrinsics<T, typename boost::disable_if_c<sizeof(T) <= sizeof(void*)>::type> {
+    public:
+
+        static T compareAndSwap(volatile T* dest, T expected, T newValue) {
+            return __sync_val_compare_and_swap(dest, expected, newValue);
+        }
+
+        static T swap(volatile T* dest, T newValue) {
+            T currentValue = *dest;
+            while (true) {
+                const T result = compareAndSwap(dest, currentValue, newValue);
+                if (result == currentValue)
+                    return result;
+                currentValue = result;
+            }
+        }
+
+        static T load(volatile const T* value) {
+            return compareAndSwap(const_cast<volatile T*>(value), T(0), T(0));
+        }
+
+        static void store(volatile T* dest, T newValue) {
+            swap(dest, newValue);
+        }
+
+        static T fetchAndAdd(volatile T* dest, T increment) {
+            return __sync_fetch_and_add(dest, increment);
+        }
+
+    private:
+        AtomicIntrinsics();
+        ~AtomicIntrinsics();
+    };
+
+}  // namespace mongo

src/mongo/util/background.h

@@ -30,6 +30,7 @@
 #pragma once
 
 #include <boost/scoped_ptr.hpp>
+#include <boost/utility.hpp>
 #include <string>
 #include <vector>
 

src/mongo/util/goodies.h

@@ -38,6 +38,7 @@
 #include <boost/scoped_array.hpp>
 #include <boost/scoped_ptr.hpp>
 #include <boost/shared_ptr.hpp>
+#include <boost/utility.hpp>
 
 #include "mongo/bson/util/misc.h"