Changes in libcfa/src/concurrency/locks.hfa [bd72c284:8a97248]

File:

• libcfa/src/concurrency/locks.hfa (modified) (10 diffs)

libcfa/src/concurrency/locks.hfa

@@ -32 +32 @@
 #include <fstream.hfa>
 
+
 // futex headers
 #include <linux/futex.h>      /* Definition of FUTEX_* constants */
@@ -154 +155 @@
 // futex_mutex
 
+// - No cond var support
 // - Kernel thd blocking alternative to the spinlock
 // - No ownership (will deadlock on reacq)
@@ -183 +185 @@
         int state;
 
-        for( int spin = 4; spin < 1024; spin += spin) {
-                state = 0;
-                // if unlocked, lock and return
-                if (internal_try_lock(this, state)) return;
-                if (2 == state) break;
-                for (int i = 0; i < spin; i++) Pause();
-        }
-
-        // // no contention try to acquire
-        // if (internal_try_lock(this, state)) return;
+        
+        // // linear backoff omitted for now
+        // for( int spin = 4; spin < 1024; spin += spin) {
+        //      state = 0;
+        //      // if unlocked, lock and return
+        //      if (internal_try_lock(this, state)) return;
+        //      if (2 == state) break;
+        //      for (int i = 0; i < spin; i++) Pause();
+        // }
+
+        // no contention try to acquire
+        if (internal_try_lock(this, state)) return;
         
         // if not in contended state, set to be in contended state
@@ -205 +209 @@
 
 static inline void unlock(futex_mutex & this) with(this) {
-        // if uncontended do atomic unlock and then return
-    if (__atomic_exchange_n(&val, 0, __ATOMIC_RELEASE) == 1) return;
+        // if uncontended do atomice unlock and then return
+        if (__atomic_fetch_sub(&val, 1, __ATOMIC_RELEASE) == 1) return; // TODO: try acq/rel
         
         // otherwise threads are blocked so we must wake one
+        __atomic_store_n((int *)&val, 0, __ATOMIC_RELEASE);
         futex((int *)&val, FUTEX_WAKE, 1);
 }
@@ -217 +222 @@
 // to set recursion count after getting signalled;
 static inline void on_wakeup( futex_mutex & f, size_t recursion ) {}
-
-//-----------------------------------------------------------------------------
-// go_mutex
-
-// - Kernel thd blocking alternative to the spinlock
-// - No ownership (will deadlock on reacq)
-// - Golang's flavour of mutex
-// - Impl taken from Golang: src/runtime/lock_futex.go
-struct go_mutex {
-        // lock state any state other than UNLOCKED is locked
-        // enum LockState { UNLOCKED = 0, LOCKED = 1, SLEEPING = 2 };
-        
-        // stores a lock state
-        int val; 
-};
-
-static inline void  ?{}( go_mutex & this ) with(this) { val = 0; }
-
-static inline bool internal_try_lock(go_mutex & this, int & compare_val, int new_val ) with(this) {
-        return __atomic_compare_exchange_n((int*)&val, (int*)&compare_val, new_val, false, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE);
-}
-
-static inline int internal_exchange(go_mutex & this, int swap ) with(this) {
-        return __atomic_exchange_n((int*)&val, swap, __ATOMIC_ACQUIRE);
-}
-
-// if this is called recursively IT WILL DEADLOCK!!!!!
-static inline void lock(go_mutex & this) with(this) {
-        int state, init_state;
-
-    // speculative grab
-    state = internal_exchange(this, 1);
-    if ( !state ) return; // state == 0
-    init_state = state;
-    for (;;) {
-        for( int i = 0; i < 4; i++ ) {
-            while( !val ) { // lock unlocked
-                state = 0;
-                if (internal_try_lock(this, state, init_state)) return;
-            }
-            for (int i = 0; i < 30; i++) Pause();
-        }
-
-        while( !val ) { // lock unlocked
-            state = 0;
-            if (internal_try_lock(this, state, init_state)) return;
-        }
-        sched_yield();
-        
-        // if not in contended state, set to be in contended state
-        state = internal_exchange(this, 2);
-        if ( !state ) return; // state == 0
-        init_state = 2;
-        futex((int*)&val, FUTEX_WAIT, 2); // if val is not 2 this returns with EWOULDBLOCK
-    }
-}
-
-static inline void unlock( go_mutex & this ) with(this) {
-        // if uncontended do atomic unlock and then return
-    if (__atomic_exchange_n(&val, 0, __ATOMIC_RELEASE) == 1) return;
-        
-        // otherwise threads are blocked so we must wake one
-        futex((int *)&val, FUTEX_WAKE, 1);
-}
-
-static inline void on_notify( go_mutex & f, thread$ * t){ unpark(t); }
-static inline size_t on_wait( go_mutex & f ) {unlock(f); return 0;}
-static inline void on_wakeup( go_mutex & f, size_t recursion ) {}
 
 //-----------------------------------------------------------------------------
@@ -316 +253 @@
 static inline void on_wakeup(clh_lock & this, size_t recursion ) { lock(this); }
 
+
 //-----------------------------------------------------------------------------
 // Exponential backoff then block lock
@@ -334 +272 @@
         this.lock_value = 0;
 }
-
-static inline void  ^?{}( exp_backoff_then_block_lock & this ){}
+static inline void ^?{}( exp_backoff_then_block_lock & this ) {}
+// static inline void ?{}( exp_backoff_then_block_lock & this, exp_backoff_then_block_lock this2 ) = void;
+// static inline void ?=?( exp_backoff_then_block_lock & this, exp_backoff_then_block_lock this2 ) = void;
 
 static inline bool internal_try_lock(exp_backoff_then_block_lock & this, size_t & compare_val) with(this) {
-        return __atomic_compare_exchange_n(&lock_value, &compare_val, 1, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
+        if (__atomic_compare_exchange_n(&lock_value, &compare_val, 1, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
+                return true;
+        }
+        return false;
 }
 
@@ -344 +286 @@
 
 static inline bool try_lock_contention(exp_backoff_then_block_lock & this) with(this) {
-        return !__atomic_exchange_n(&lock_value, 2, __ATOMIC_ACQUIRE);
+        if (__atomic_exchange_n(&lock_value, 2, __ATOMIC_ACQUIRE) == 0) {
+                return true;
+        }
+        return false;
 }
 
 static inline bool block(exp_backoff_then_block_lock & this) with(this) {
-    lock( spinlock __cfaabi_dbg_ctx2 );
-    if (__atomic_load_n( &lock_value, __ATOMIC_SEQ_CST) != 2) {
-        unlock( spinlock );
-        return true;
-    }
-    insert_last( blocked_threads, *active_thread() );
-    unlock( spinlock );
+        lock( spinlock __cfaabi_dbg_ctx2 ); // TODO change to lockfree queue (MPSC)
+        if (lock_value != 2) {
+                unlock( spinlock );
+                return true;
+        }
+        insert_last( blocked_threads, *active_thread() );
+        unlock( spinlock );
         park( );
         return true;
@@ -362 +307 @@
         size_t compare_val = 0;
         int spin = 4;
-
         // linear backoff
         for( ;; ) {
@@ -380 +324 @@
 static inline void unlock(exp_backoff_then_block_lock & this) with(this) {
     if (__atomic_exchange_n(&lock_value, 0, __ATOMIC_RELEASE) == 1) return;
-    lock( spinlock __cfaabi_dbg_ctx2 );
-    thread$ * t = &try_pop_front( blocked_threads );
-    unlock( spinlock );
-    unpark( t );
+        lock( spinlock __cfaabi_dbg_ctx2 );
+        thread$ * t = &try_pop_front( blocked_threads );
+        unlock( spinlock );
+        unpark( t );
 }