Remove static initializer; fix endian-ness detection; fix build on

various platforms; improve android port speed.

Avoid static initializer by using a new portability interface for
thread-safe lazy initialization.  Custom ports will need to be
extended to implement InitOnce/OnceType/LEVELDB_ONCE_INIT.

Fix endian-ness detection (fixes Powerpc builds).

Build related fixes:
- Support platforms that have unversioned shared libraries.
- Fix IOS build rules.

Android improvements
- Speed up atomic pointers
- Share more code with port_posix.

Do not spin in a tight loop attempting compactions if the file system
is inaccessible (e.g., if kerberos tickets have expired or if it is out
of space).

5 files changed, 51 insertions, 16 deletions

diff --git a/port/atomic_pointer.h b/port/atomic_pointer.h
index 35ae550..c58bffb 100644
--- a/port/atomic_pointer.h
+++ b/port/atomic_pointer.h
@@ -73,13 +73,21 @@ inline void MemoryBarrier() {
 }
 #define LEVELDB_HAVE_MEMORY_BARRIER
 
-// ARM
-#elif defined(ARCH_CPU_ARM_FAMILY)
+// ARM Linux
+#elif defined(ARCH_CPU_ARM_FAMILY) && defined(__linux__)
 typedef void (*LinuxKernelMemoryBarrierFunc)(void);
-LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
-    (LinuxKernelMemoryBarrierFunc) 0xffff0fa0;
+// The Linux ARM kernel provides a highly optimized device-specific memory
+// barrier function at a fixed memory address that is mapped in every
+// user-level process.
+//
+// This beats using CPU-specific instructions which are, on single-core
+// devices, un-necessary and very costly (e.g. ARMv7-A "dmb" takes more
+// than 180ns on a Cortex-A8 like the one on a Nexus One). Benchmarking
+// shows that the extra function call cost is completely negligible on
+// multi-core devices.
+//
 inline void MemoryBarrier() {
-  pLinuxKernelMemoryBarrier();
+  (*(LinuxKernelMemoryBarrierFunc)0xffff0fa0)();
 }
 #define LEVELDB_HAVE_MEMORY_BARRIER
 
diff --git a/port/port.h b/port/port.h
index 816826b..e667db4 100644
--- a/port/port.h
+++ b/port/port.h
@@ -14,8 +14,6 @@
 #  include "port/port_posix.h"
 #elif defined(LEVELDB_PLATFORM_CHROMIUM)
 #  include "port/port_chromium.h"
-#elif defined(LEVELDB_PLATFORM_ANDROID)
-#  include "port/port_android.h"
 #endif
 
 #endif  // STORAGE_LEVELDB_PORT_PORT_H_
diff --git a/port/port_example.h b/port/port_example.h
index 036c7d1..ab9e489 100644
--- a/port/port_example.h
+++ b/port/port_example.h
@@ -60,6 +60,16 @@ class CondVar {
   void SignallAll();
 };
 
+// Thread-safe initialization.
+// Used as follows:
+//      static port::OnceType init_control = LEVELDB_ONCE_INIT;
+//      static void Initializer() { ... do something ...; }
+//      ...
+//      port::InitOnce(&init_control, &Initializer);
+typedef intptr_t OnceType;
+#define LEVELDB_ONCE_INIT 0
+extern void InitOnce(port::OnceType*, void (*initializer)());
+
 // A type that holds a pointer that can be read or written atomically
 // (i.e., without word-tearing.)
 class AtomicPointer {
diff --git a/port/port_posix.cc b/port/port_posix.cc
index c44cc99..5ba127a 100644
--- a/port/port_posix.cc
+++ b/port/port_posix.cc
@@ -46,5 +46,9 @@ void CondVar::SignalAll() {
   PthreadCall("broadcast", pthread_cond_broadcast(&cv_));
 }
 
+void InitOnce(OnceType* once, void (*initializer)()) {
+  PthreadCall("once", pthread_once(once, initializer));
+}
+
 }  // namespace port
 }  // namespace leveldb
diff --git a/port/port_posix.h b/port/port_posix.h
index 485ad10..654a4b9 100644
--- a/port/port_posix.h
+++ b/port/port_posix.h
@@ -7,17 +7,22 @@
 #ifndef STORAGE_LEVELDB_PORT_PORT_POSIX_H_
 #define STORAGE_LEVELDB_PORT_PORT_POSIX_H_
 
+#undef PLATFORM_IS_LITTLE_ENDIAN
 #if defined(OS_MACOSX)
   #include <machine/endian.h>
+  #if defined(__DARWIN_LITTLE_ENDIAN) && defined(__DARWIN_BYTE_ORDER)
+    #define PLATFORM_IS_LITTLE_ENDIAN \
+        (__DARWIN_BYTE_ORDER == __DARWIN_LITTLE_ENDIAN)
+  #endif
 #elif defined(OS_SOLARIS)
   #include <sys/isa_defs.h>
   #ifdef _LITTLE_ENDIAN
-    #define LITTLE_ENDIAN
+    #define PLATFORM_IS_LITTLE_ENDIAN true
   #else
-    #define BIG_ENDIAN
+    #define PLATFORM_IS_LITTLE_ENDIAN false
   #endif
 #elif defined(OS_FREEBSD) || defined(OS_OPENBSD) || defined(OS_NETBSD) ||\
-      defined(OS_DRAGONFLYBSD)
+      defined(OS_DRAGONFLYBSD) || defined(OS_ANDROID)
   #include <sys/types.h>
   #include <sys/endian.h>
 #else
@@ -31,14 +36,13 @@
 #include <string>
 #include "port/atomic_pointer.h"
 
-#ifdef LITTLE_ENDIAN
-#define IS_LITTLE_ENDIAN true
-#else
-#define IS_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
+#ifndef PLATFORM_IS_LITTLE_ENDIAN
+#define PLATFORM_IS_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
 #endif
 
 #if defined(OS_MACOSX) || defined(OS_SOLARIS) || defined(OS_FREEBSD) ||\
-    defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_DRAGONFLYBSD)
+    defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_DRAGONFLYBSD) ||\
+    defined(OS_ANDROID)
 // Use fread/fwrite/fflush on platforms without _unlocked variants
 #define fread_unlocked fread
 #define fwrite_unlocked fwrite
@@ -51,10 +55,17 @@
 #define fdatasync fsync
 #endif
 
+#if defined(OS_ANDROID) && __ANDROID_API__ < 9
+// fdatasync() was only introduced in API level 9 on Android. Use fsync()
+// when targetting older platforms.
+#define fdatasync fsync
+#endif
+
 namespace leveldb {
 namespace port {
 
-static const bool kLittleEndian = IS_LITTLE_ENDIAN;
+static const bool kLittleEndian = PLATFORM_IS_LITTLE_ENDIAN;
+#undef PLATFORM_IS_LITTLE_ENDIAN
 
 class CondVar;
 
@@ -88,6 +99,10 @@ class CondVar {
   Mutex* mu_;
 };
 
+typedef pthread_once_t OnceType;
+#define LEVELDB_ONCE_INIT PTHREAD_ONCE_INIT
+extern void InitOnce(OnceType* once, void (*initializer)());
+
 inline bool Snappy_Compress(const char* input, size_t length,
                             ::std::string* output) {
 #ifdef SNAPPY