Platform detection during build, plus compatibility patches for machi…

…nes without <cstdatomic>.

This revision adds two major changes:
1. build_detect_platform which generates build_config.mk
   with platform-dependent flags for the build process
2. /port/atomic_pointer.h with anAtomicPointerimplementation
   for platforms without <cstdatomic>

Some of this code is loosely based on patches submitted to the 
LevelDB mailing list at https://groups.google.com/forum/#!forum/leveldb
Tip of the hat to Dave Smith and Edouard A, who both sent patches.

The presence of Snappy (http://code.google.com/p/snappy/) and
cstdatomic are now both detected in the build_detect_platform
script (1.) which gets executing during make.

For (2.), instead of broadly importing atomicops_* from Chromium or
the Google performance tools, we chose to just implement AtomicPointer 
and the limited atomic load and store operations it needs. 
This resulted in much less code and fewer files - everything is 
contained in atomic_pointer.h.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@34 62dab493-f737-651d-591e-8d6aee1b9529

Makefile

@@ -13,37 +13,32 @@ OPT = -O2 -DNDEBUG       # (A) Production use (optimized mode)
 # OPT = -O2 -g2 -DNDEBUG # (C) Profiling mode: opt, but w/debugging symbols
 #-----------------------------------------------
 
+# detect what platform we're building on
+$(shell sh ./build_detect_platform)
+# this file is generated by build_detect_platform to set build flags
+include build_config.mk
 
-UNAME := $(shell uname)
-
-ifeq ($(UNAME), Darwin)
-# To build for iOS, set PLATFORM=IOS.
-ifndef PLATFORM
-PLATFORM=OSX
-endif # PLATFORM
-PLATFORM_CFLAGS = -DLEVELDB_PLATFORM_OSX
-PORT_MODULE = port_osx.o
-else # UNAME
-PLATFORM_CFLAGS = -DLEVELDB_PLATFORM_POSIX -std=c++0x
-PORT_MODULE = port_posix.o
-endif # UNAME
-
-# Set 'SNAPPY' to 1 if you have the Snappy compression library
-# installed and want to enable its use in LevelDB
+# If Snappy is installed, add compilation and linker flags
 # (see http://code.google.com/p/snappy/)
-SNAPPY=0
-
-ifeq ($(SNAPPY), 0)
+ifeq ($(SNAPPY), 1)
+SNAPPY_CFLAGS=-DSNAPPY
+SNAPPY_LDFLAGS=-lsnappy
+else
 SNAPPY_CFLAGS=
 SNAPPY_LDFLAGS=
+endif
+
+# If Google Perf Tools are installed, add compilation and linker flags
+# (see http://code.google.com/p/google-perftools/)
+ifeq ($(GOOGLE_PERFTOOLS), 1)
+GOOGLE_PERFTOOLS_LDFLAGS=-ltcmalloc
 else
-SNAPPY_CFLAGS=-DSNAPPY
-SNAPPY_LDFLAGS=-lsnappy
+GOOGLE_PERFTOOLS_LDFLAGS=
 endif
 
-CFLAGS = -c -I. -I./include $(PLATFORM_CFLAGS) $(OPT) $(SNAPPY_CFLAGS)
+CFLAGS = -c -I. -I./include $(PORT_CFLAGS) $(PLATFORM_CCFLAGS) $(OPT) $(SNAPPY_CFLAGS)
 
-LDFLAGS=-lpthread $(SNAPPY_LDFLAGS)
+LDFLAGS=$(PLATFORM_LDFLAGS) $(SNAPPY_LDFLAGS) $(GOOGLE_PERFTOOLS_LDFLAGS)
 
 LIBOBJECTS = \
 	./db/builder.o \
@@ -59,7 +54,7 @@ LIBOBJECTS = \
 	./db/version_edit.o \
 	./db/version_set.o \
 	./db/write_batch.o \
-	./port/$(PORT_MODULE) \
+	./port/port_posix.o \
 	./table/block.o \
 	./table/block_builder.o \
 	./table/format.o \
@@ -105,19 +100,15 @@ PROGRAMS = db_bench $(TESTS)
 
 LIBRARY = libleveldb.a
 
-ifeq ($(PLATFORM), IOS)
-# Only XCode can build executable applications for iOS.
 all: $(LIBRARY)
-else
-all: $(PROGRAMS) $(LIBRARY)
-endif
 
-check: $(TESTS)
+check: $(PROGRAMS) $(TESTS)
 	for t in $(TESTS); do echo "***** Running $$t"; ./$$t || exit 1; done
 
 clean:
 	-rm -f $(PROGRAMS) $(LIBRARY) */*.o ios-x86/*/*.o ios-arm/*/*.o
-	-rmdir -p ios-x86/* ios-arm/*
+	-rm -rf ios-x86/* ios-arm/*
+	-rm build_config.mk
 
 $(LIBRARY): $(LIBOBJECTS)
 	rm -f $@
@@ -188,5 +179,3 @@ else
 	$(CC) $(CFLAGS) $< -o $@
 endif
 
-# TODO(gabor): dependencies for .o files
-# TODO(gabor): Build library

build_detect_platform

@@ -0,0 +1,69 @@
+#!/bin/sh
+
+# Detects OS we're compiling on and generates build_config.mk,
+# which in turn gets read while processing Makefile.
+
+# build_config.mk will set the following variables:
+# - PORT_CFLAGS will either set:
+#               -DLEVELDB_PLATFORM_POSIX if cstatomic is present
+#               -DLEVELDB_PLATFORM_NOATOMIC if it is not
+# - PLATFORM_CFLAGS with compiler flags for the platform
+# - PLATFORM_LDFLAGS with linker flags for the platform
+
+# Delete existing build_config.mk
+rm -f build_config.mk
+
+# Detect OS
+case `uname -s` in
+    Darwin)
+        PLATFORM=OS_MACOSX
+        echo "PLATFORM_CFLAGS=-pthread -DOS_MACOSX" >> build_config.mk
+        echo "PLATFORM_LDFLAGS=-lpthread"  >> build_config.mk
+        ;;
+    Linux)
+        PLATFORM=OS_LINUX
+        echo "PLATFORM_CFLAGS=-pthread -DOS_LINUX" >> build_config.mk
+        echo "PLATFORM_LDFLAGS=-lpthread"  >> build_config.mk
+        ;;
+    SunOS)
+        PLATFORM=OS_SOLARIS
+        echo "PLATFORM_CFLAGS=-D_REENTRANT -DOS_SOLARIS"  >> build_config.mk
+        echo "PLATFORM_LDFLAGS=-lpthread -lrt" >> build_config.mk
+        ;;
+    *)
+        echo "Unknown platform!"
+        exit 1
+esac
+
+echo "PLATFORM=$PLATFORM" >> build_config.mk
+
+# On GCC, use libc's memcmp, not GCC's memcmp
+PORT_CFLAGS="-fno-builtin-memcmp"
+
+# Detect C++0x -- this determines whether we'll use port_noatomic.h
+# or port_posix.h by:
+# 1. Rrying to compile with -std=c++0x and including <cstdatomic>.
+# 2. If g++ returns error code, we know to use port_posix.h
+g++ $CFLAGS -std=c++0x -x c++ - -o /dev/null 2>/dev/null  <<EOF
+  #include <cstdatomic>
+  int main() {}
+EOF
+if [ "$?" = 0 ]; then
+    PORT_CFLAGS+=" -DLEVELDB_PLATFORM_POSIX -DLEVELDB_CSTDATOMIC_PRESENT -std=c++0x"
+else
+    PORT_CFLAGS+=" -DLEVELDB_PLATFORM_POSIX"
+fi
+
+# Test whether Snappy library is installed
+# http://code.google.com/p/snappy/
+g++ $CFLAGS -x c++ - -o /dev/null 2>/dev/null  <<EOF
+  #include <snappy.h>
+  int main() {}
+EOF
+if [ "$?" = 0 ]; then
+    echo "SNAPPY=1" >> build_config.mk
+else
+    echo "SNAPPY=0" >> build_config.mk
+fi
+
+echo "PORT_CFLAGS=$PORT_CFLAGS" >> build_config.mk

port/atomic_pointer.h

@@ -0,0 +1,213 @@
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+// AtomicPointer provides storage for a lock-free pointer.
+// Platform-dependent implementation of AtomicPointer:
+// - If cstdatomic is present (on newer versions of gcc, it is), we use
+//   a cstdatomic-based AtomicPointer
+// - If it is not, we define processor-dependent AtomicWord operations,
+//   and then use them to build AtomicPointer
+//
+// This code is based on atomicops-internals-* in Google's perftools:
+// http://code.google.com/p/google-perftools/source/browse/#svn%2Ftrunk%2Fsrc%2Fbase
+
+#ifndef PORT_ATOMIC_POINTER_H_
+#define PORT_ATOMIC_POINTER_H_
+
+#ifdef LEVELDB_CSTDATOMIC_PRESENT
+
+///////////////////////////////////////////////////////////////////////////////
+// WE HAVE <cstdatomic>
+// Use a <cstdatomic>-based AtomicPointer
+
+#include <cstdatomic>
+#include <stdint.h>
+
+namespace leveldb {
+namespace port {
+
+// Storage for a lock-free pointer
+class AtomicPointer {
+ private:
+  std::atomic<void*> rep_;
+ public:
+  AtomicPointer() { }
+  explicit AtomicPointer(void* v) : rep_(v) { }
+  inline void* Acquire_Load() const {
+    return rep_.load(std::memory_order_acquire);
+  }
+  inline void Release_Store(void* v) {
+    rep_.store(v, std::memory_order_release);
+  }
+  inline void* NoBarrier_Load() const {
+    return rep_.load(std::memory_order_relaxed);
+  }
+  inline void NoBarrier_Store(void* v) {
+    rep_.store(v, std::memory_order_relaxed);
+  }
+};
+
+} // namespace leveldb::port
+} // namespace leveldb
+
+#else
+///////////////////////////////////////////////////////////////////////////////
+// NO <cstdatomic>
+// The entire rest of this file covers that case
+
+#if defined(_M_X64) || defined(__x86_64__)
+#define ARCH_CPU_X86_FAMILY 1
+#elif defined(_M_IX86) || defined(__i386__) || defined(__i386)
+#define ARCH_CPU_X86_FAMILY 1
+#elif defined(__ARMEL__)
+#define ARCH_CPU_ARM_FAMILY 1
+#else
+#warning Please add support for your architecture in atomicpointer.h
+#endif
+
+namespace leveldb {
+namespace port {
+namespace internal {
+
+// AtomicWord is a machine-sized pointer.
+typedef intptr_t AtomicWord;
+
+} // namespace leveldb::port::internal
+} // namespace leveldb::port
+} // namespace leveldb
+
+// Include our platform specific implementation.
+///////////////////////////////////////////////////////////////////////////////
+// Windows on x86
+#if defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY)
+
+// void MemoryBarrier(void) macro is defined in windows.h:
+// http://msdn.microsoft.com/en-us/library/ms684208(v=vs.85).aspx
+// Including windows.h here; MemoryBarrier() gets used below.
+#include <windows.h>
+
+///////////////////////////////////////////////////////////////////////////////
+// Mac OS on x86
+#elif defined(OS_MACOSX) && defined(ARCH_CPU_X86_FAMILY)
+
+#include <libkern/OSAtomic.h>
+
+namespace leveldb {
+namespace port {
+namespace internal {
+
+inline void MemoryBarrier() {
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+  // See http://gcc.gnu.org/ml/gcc/2003-04/msg01180.html for a discussion on
+  // this idiom. Also see http://en.wikipedia.org/wiki/Memory_ordering.
+  __asm__ __volatile__("" : : : "memory");
+#else
+  OSMemoryBarrier();
+#endif
+}
+
+} // namespace leveldb::port::internal
+} // namespace leveldb::port
+} // namespace leveldb
+
+///////////////////////////////////////////////////////////////////////////////
+// Any x86 CPU
+#elif defined(ARCH_CPU_X86_FAMILY)
+
+namespace leveldb {
+namespace port {
+namespace internal {
+
+inline void MemoryBarrier() {
+  __asm__ __volatile__("" : : : "memory");
+}
+
+} // namespace leveldb::port::internal
+} // namespace leveldb::port
+} // namespace leveldb
+
+#undef ATOMICOPS_COMPILER_BARRIER
+
+///////////////////////////////////////////////////////////////////////////////
+// ARM
+#elif defined(ARCH_CPU_ARM_FAMILY)
+
+namespace leveldb {
+namespace port {
+namespace internal {
+
+typedef void (*LinuxKernelMemoryBarrierFunc)(void);
+LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
+    (LinuxKernelMemoryBarrierFunc) 0xffff0fa0;
+
+inline void MemoryBarrier() {
+  pLinuxKernelMemoryBarrier();
+}
+
+} // namespace leveldb::port::internal
+} // namespace leveldb::port
+} // namespace leveldb
+
+#else
+#error "Atomic operations are not supported on your platform"
+#endif
+
+///////////////////////////////////////////////////////////////////////////////
+// Implementation of AtomicPointer based on MemoryBarriers above
+
+namespace leveldb {
+namespace port {
+namespace internal {
+
+// Atomic operations using per-system MemoryBarrier()s
+
+inline AtomicWord Acquire_Load(volatile const AtomicWord* ptr) {
+  AtomicWord value = *ptr;
+  MemoryBarrier();
+  return value;
+}
+
+inline void Release_Store(volatile AtomicWord* ptr, AtomicWord value) {
+  MemoryBarrier();
+  *ptr = value;
+}
+
+inline AtomicWord NoBarrier_Load(volatile const AtomicWord* ptr) {
+  return *ptr;
+}
+
+inline void NoBarrier_Store(volatile AtomicWord* ptr, AtomicWord value) {
+  *ptr = value;
+}
+
+} // namespace leveldb::port::internal
+
+// AtomicPointer definition for systems without <cstdatomic>.
+class AtomicPointer {
+ private:
+  typedef internal::AtomicWord Rep;
+  Rep rep_;
+ public:
+  AtomicPointer() { }
+  explicit AtomicPointer(void* p) : rep_(reinterpret_cast<Rep>(p)) {}
+  inline void* Acquire_Load() const {
+    return reinterpret_cast<void*>(internal::Acquire_Load(&rep_));
+  }
+  inline void Release_Store(void* v) {
+    internal::Release_Store(&rep_, reinterpret_cast<Rep>(v));
+  }
+  inline void* NoBarrier_Load() const {
+    return reinterpret_cast<void*>(internal::NoBarrier_Load(&rep_));
+  }
+  inline void NoBarrier_Store(void* v) {
+    internal::NoBarrier_Store(&rep_, reinterpret_cast<Rep>(v));
+  }
+};
+
+} // namespace leveldb::port
+} // namespace leveldb
+
+#endif // LEVELDB_CSTDATOMIC_PRESENT
+
+#endif  // PORT_ATOMIC_POINTER_H_

port/port.h

@@ -16,8 +16,6 @@
 #  include "port/port_chromium.h"
 #elif defined(LEVELDB_PLATFORM_ANDROID)
 #  include "port/port_android.h"
-#elif defined(LEVELDB_PLATFORM_OSX)
-#  include "port/port_osx.h"
 #endif
 
 #endif  // STORAGE_LEVELDB_PORT_PORT_H_