Simplify locking with C++11 atomics (#2382)

src/s3fs.cpp

@@ -19,6 +19,7 @@
  */
 
 #include <algorithm>
+#include <atomic>
 #include <cerrno>
 #include <cstdio>
 #include <cstdlib>
@@ -205,15 +206,13 @@ static int s3fs_removexattr(const char* path, const char* name);
 class MpStatFlag
 {
     private:
-        mutable pthread_mutex_t flag_lock;
-        bool                    is_lock_init = false;
-        bool                    has_mp_stat = false;
+        std::atomic<bool>       has_mp_stat;
 
     public:
-        MpStatFlag();
+        MpStatFlag() = default;
         MpStatFlag(const MpStatFlag&) = delete;
         MpStatFlag(MpStatFlag&&) = delete;
-        ~MpStatFlag();
+        ~MpStatFlag() = default;
         MpStatFlag& operator=(const MpStatFlag&) = delete;
         MpStatFlag& operator=(MpStatFlag&&) = delete;
 
@@ -221,46 +220,14 @@ class MpStatFlag
         bool Set(bool flag);
 };
 
-MpStatFlag::MpStatFlag()
-{
-    pthread_mutexattr_t attr;
-    pthread_mutexattr_init(&attr);
-#if S3FS_PTHREAD_ERRORCHECK
-    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK);
-#endif
-
-    int result;
-    if(0 != (result = pthread_mutex_init(&flag_lock, &attr))){
-        S3FS_PRN_CRIT("failed to init flag_lock: %d", result);
-        abort();
-    }
-    is_lock_init = true;
-}
-
-MpStatFlag::~MpStatFlag()
-{
-    if(is_lock_init){
-        int result;
-        if(0 != (result = pthread_mutex_destroy(&flag_lock))){
-            S3FS_PRN_CRIT("failed to destroy flag_lock: %d", result);
-            abort();
-        }
-        is_lock_init = false;
-    }
-}
-
 bool MpStatFlag::Get()
 {
-    AutoLock auto_lock(&flag_lock);
     return has_mp_stat;
 }
 
 bool MpStatFlag::Set(bool flag)
 {
-    AutoLock auto_lock(&flag_lock);
-    bool old    = has_mp_stat;
-    has_mp_stat = flag;
-    return old;
+    return has_mp_stat.exchange(flag);
 }
 
 // whether the stat information file for mount point exists

src/threadpoolman.cpp

@@ -117,7 +117,7 @@ void* ThreadPoolMan::Worker(void* arg)
 //------------------------------------------------
 // ThreadPoolMan methods
 //------------------------------------------------
-ThreadPoolMan::ThreadPoolMan(int count) : is_exit(false), thpoolman_sem(0), is_lock_init(false), is_exit_flag_init(false)
+ThreadPoolMan::ThreadPoolMan(int count) : is_exit(false), thpoolman_sem(0), is_lock_init(false)
 {
     if(count < 1){
         S3FS_PRN_CRIT("Failed to creating singleton for Thread Manager, because thread count(%d) is under 1.", count);
@@ -141,12 +141,6 @@ ThreadPoolMan::ThreadPoolMan(int count) : is_exit(false), thpoolman_sem(0), is_l
     }
     is_lock_init = true;
 
-    if(0 != (result = pthread_mutex_init(&thread_exit_flag_lock, &attr))){
-        S3FS_PRN_CRIT("failed to init thread_exit_flag_lock: %d", result);
-        abort();
-    }
-    is_exit_flag_init = true;
-
     // create threads
     if(!StartThreads(count)){
         S3FS_PRN_ERR("Failed starting threads at initializing.");
@@ -166,25 +160,15 @@ ThreadPoolMan::~ThreadPoolMan()
         }
         is_lock_init = false;
     }
-    if(is_exit_flag_init ){
-        int result;
-        if(0 != (result = pthread_mutex_destroy(&thread_exit_flag_lock))){
-            S3FS_PRN_CRIT("failed to destroy thread_exit_flag_lock: %d", result);
-            abort();
-        }
-        is_exit_flag_init  = false;
-    }
 }
 
 bool ThreadPoolMan::IsExit() const
 {
-    AutoLock auto_lock(&thread_exit_flag_lock);
     return is_exit;
 }
 
 void ThreadPoolMan::SetExitFlag(bool exit_flag)
 {
-    AutoLock auto_lock(&thread_exit_flag_lock);
     is_exit = exit_flag;
 }
 

src/threadpoolman.h

@@ -21,6 +21,7 @@
 #ifndef S3FS_THREADPOOLMAN_H_
 #define S3FS_THREADPOOLMAN_H_
 
+#include <atomic>
 #include <list>
 #include <memory>
 #include <vector>
@@ -64,7 +65,7 @@ class ThreadPoolMan
     private:
         static ThreadPoolMan* singleton;
 
-        bool                  is_exit;
+        std::atomic<bool>     is_exit;
         Semaphore             thpoolman_sem;
 
         bool                  is_lock_init;
@@ -73,9 +74,6 @@ class ThreadPoolMan
 
         thpoolman_params_t    instruction_list;
 
-        bool                  is_exit_flag_init;
-        mutable pthread_mutex_t thread_exit_flag_lock;
-
     private:
         static void* Worker(void* arg);