[RocksDB] Introduce Fast Mutex option

Summary:
This diff adds an option to specify whether PTHREAD_MUTEX_ADAPTIVE_NP will be enabled for the rocksdb single big kernel lock. db_bench also have this option now.
Quickly tested 8 thread cpu bound 100 byte random read.
No fast mutex: ~750k/s ops
With fast mutex: ~880k/s ops

Test Plan: make check; db_bench; db_stress

Reviewers: dhruba

CC: MarkCallaghan, leveldb

Differential Revision: https://reviews.facebook.net/D11031

port/port_posix.cc

@@ -19,7 +19,24 @@ static void PthreadCall(const char* label, int result) {
   }
 }
 
-Mutex::Mutex() { PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL)); }
+Mutex::Mutex(bool adaptive) {
+#ifdef OS_LINUX
+  if (!adaptive) {
+    PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL));
+  } else {
+    pthread_mutexattr_t mutex_attr;
+    PthreadCall("init mutex attr", pthread_mutexattr_init(&mutex_attr));
+    PthreadCall("set mutex attr",
+                pthread_mutexattr_settype(&mutex_attr,
+                                          PTHREAD_MUTEX_ADAPTIVE_NP));
+    PthreadCall("init mutex", pthread_mutex_init(&mu_, &mutex_attr));
+    PthreadCall("destroy mutex attr",
+                pthread_mutexattr_destroy(&mutex_attr));
+  }
+#else // ignore adaptive for non-linux platform
+  PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL));
+#endif // OS_LINUX
+}
 
 Mutex::~Mutex() { PthreadCall("destroy mutex", pthread_mutex_destroy(&mu_)); }
 

port/port_posix.h

@@ -82,7 +82,7 @@ class CondVar;
 
 class Mutex {
  public:
-  Mutex();
+  Mutex(bool adaptive = false);
   ~Mutex();
 
   void Lock();