Changeset b77f0e1 for libcfa/src

Timestamp:

Nov 14, 2022, 11:52:40 AM (2 years ago)

Author:

caparson <caparson@…>

Branches:

ADT, ast-experimental, master

Children:

63be3387

Parents:

bc899d6

Message:

cleaned up some lock stuff

File:

• libcfa/src/concurrency/locks.hfa (modified) (20 diffs)

libcfa/src/concurrency/locks.hfa

@@ -30 +30 @@
 #include "time.hfa"
 
+#include <fstream.hfa>
+
+
+// futex headers
+#include <linux/futex.h>      /* Definition of FUTEX_* constants */
+#include <sys/syscall.h>      /* Definition of SYS_* constants */
+#include <unistd.h>
+
 //-----------------------------------------------------------------------------
 // Semaphore
@@ -140 +148 @@
 
 //-----------------------------------------------------------------------------
+// futex_mutex
+
+// - No cond var support
+// - Kernel thd blocking alternative to the spinlock
+// - No ownership (will deadlock on reacq)
+struct futex_mutex {
+        // lock state any state other than UNLOCKED is locked
+        // enum LockState { UNLOCKED = 0, UNCONTENDED = 1, CONTENDED = 2 };
+        
+        // stores a lock state
+        int val; 
+};
+
+// to use for FUTEX_WAKE and FUTEX_WAIT (other futex calls will need more params)
+static int futex(int *uaddr, int futex_op, int val) {
+    return syscall(SYS_futex, uaddr, futex_op, val, NULL, NULL, 0);
+}
+
+static inline void  ?{}( futex_mutex & this ) with(this) { val = 0; }
+
+static inline bool internal_try_lock(futex_mutex & this, int & compare_val) with(this) {
+        return __atomic_compare_exchange_n((int*)&val, (int*)&compare_val, 1, false, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE);
+}
+
+static inline int internal_exchange(futex_mutex & this) with(this) {
+        return __atomic_exchange_n((int*)&val, 2, __ATOMIC_ACQUIRE);
+}
+
+// if this is called recursively IT WILL DEADLOCK!!!!!
+static inline void lock(futex_mutex & this) with(this) {
+        int state;
+
+        
+        // linear backoff
+        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();
+        }
+        // if (internal_try_lock(this, state)) return;
+        
+        // if not in contended state, set to be in contended state
+        if (state != 2) state = internal_exchange(this);
+
+        // block and spin until we win the lock
+        while (state != 0) {
+                futex((int*)&val, FUTEX_WAIT, 2); // if val is not 2 this returns with EWOULDBLOCK
+                state = internal_exchange(this);
+        }
+}
+
+static inline void unlock(futex_mutex & this) with(this) {
+        // 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);
+}
+
+static inline void on_notify( futex_mutex & f, thread$ * t){ unpark(t); }
+static inline size_t on_wait( futex_mutex & f ) {unlock(f); return 0;}
+
+// to set recursion count after getting signalled;
+static inline void on_wakeup( futex_mutex & f, size_t recursion ) {}
+
+//-----------------------------------------------------------------------------
 // CLH Spinlock
 // - No recursive acquisition
@@ -165 +242 @@
 }
 
+static inline void on_notify(clh_lock & this, struct thread$ * t ) { unpark(t); }
+static inline size_t on_wait(clh_lock & this) { unlock(this); return 0; }
+static inline void on_wakeup(clh_lock & this, size_t recursion ) {
+        #ifdef REACQ
+        lock(this);
+        #endif
+}
+
+
 //-----------------------------------------------------------------------------
 // Linear backoff Spinlock
@@ -171 +257 @@
         __spinlock_t spinlock;
 
-        // Current thread owning the lock
-        struct thread$ * owner;
-
         // List of blocked threads
         dlist( thread$ ) blocked_threads;
@@ -179 +262 @@
         // Used for comparing and exchanging
         volatile size_t lock_value;
-
-        // used for linear backoff spinning
-        int spin_start;
-        int spin_end;
-        int spin_count;
-
-        // after unsuccessful linear backoff yield this many times
-        int yield_count;
-};
-
-static inline void  ?{}( linear_backoff_then_block_lock & this, int spin_start, int spin_end, int spin_count, int yield_count ) {
+};
+
+static inline void  ?{}( linear_backoff_then_block_lock & this ) {
         this.spinlock{};
         this.blocked_threads{};
         this.lock_value = 0;
-        this.spin_start = spin_start;
-        this.spin_end = spin_end;
-        this.spin_count = spin_count;
-        this.yield_count = yield_count;
-}
-static inline void  ?{}( linear_backoff_then_block_lock & this ) { this{4, 1024, 16, 0}; }
+}
 static inline void ^?{}( linear_backoff_then_block_lock & this ) {}
-static inline void ?{}( linear_backoff_then_block_lock & this, linear_backoff_then_block_lock this2 ) = void;
-static inline void ?=?( linear_backoff_then_block_lock & this, linear_backoff_then_block_lock this2 ) = void;
+// static inline void ?{}( linear_backoff_then_block_lock & this, linear_backoff_then_block_lock this2 ) = void;
+// static inline void ?=?( linear_backoff_then_block_lock & this, linear_backoff_then_block_lock this2 ) = void;
 
 static inline bool internal_try_lock(linear_backoff_then_block_lock & this, size_t & compare_val) with(this) {
         if (__atomic_compare_exchange_n(&lock_value, &compare_val, 1, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
-                owner = active_thread();
                 return true;
         }
@@ -215 +284 @@
 static inline bool try_lock_contention(linear_backoff_then_block_lock & this) with(this) {
         if (__atomic_exchange_n(&lock_value, 2, __ATOMIC_ACQUIRE) == 0) {
-                owner = active_thread();
                 return true;
         }
@@ -234 +302 @@
 
 static inline void lock(linear_backoff_then_block_lock & this) with(this) {
-        // if owner just return
-        if (active_thread() == owner) return;
         size_t compare_val = 0;
-        int spin = spin_start;
+        int spin = 4;
         // linear backoff
         for( ;; ) {
@@ -244 +310 @@
                 if (2 == compare_val) break;
                 for (int i = 0; i < spin; i++) Pause();
-                if (spin >= spin_end) break;
+                if (spin >= 1024) break;
                 spin += spin;
         }
@@ -254 +320 @@
 
 static inline void unlock(linear_backoff_then_block_lock & this) with(this) {
-        verify(lock_value > 0);
-    owner = 0p;
     if (__atomic_exchange_n(&lock_value, 0, __ATOMIC_RELEASE) == 1) return;
         lock( spinlock __cfaabi_dbg_ctx2 );
@@ -265 +329 @@
 static inline void on_notify(linear_backoff_then_block_lock & this, struct thread$ * t ) { unpark(t); }
 static inline size_t on_wait(linear_backoff_then_block_lock & this) { unlock(this); return 0; }
-static inline void on_wakeup(linear_backoff_then_block_lock & this, size_t recursion ) { lock(this); }
+static inline void on_wakeup(linear_backoff_then_block_lock & this, size_t recursion ) { 
+        #ifdef REACQ
+        lock(this);
+        #endif
+}
 
 //-----------------------------------------------------------------------------
@@ -306 +374 @@
         assert(!(held && owner == active_thread()));
         #endif
-        if (held) {
+        if ( held ) {
                 insert_last( blocked_threads, *active_thread() );
                 unlock( lock );
@@ -331 +399 @@
 }
 
-static inline void on_notify(fast_block_lock & this, struct thread$ * t ) { unpark(t); }
+static inline void on_notify(fast_block_lock & this, struct thread$ * t ) with(this) {
+        #ifdef REACQ
+                lock( lock __cfaabi_dbg_ctx2 );
+                insert_last( blocked_threads, *t );
+                unlock( lock );
+        #else
+                unpark(t);
+        #endif
+}
 static inline size_t on_wait(fast_block_lock & this) { unlock(this); return 0; }
 static inline void on_wakeup(fast_block_lock & this, size_t recursion ) { }
@@ -412 +488 @@
         if ( owner != 0p ) {
                 insert_last( blocked_threads, *t );
-                unlock( lock );
         }
         // lock not held
@@ -419 +494 @@
                 recursion_count = 1;
                 unpark( t );
-                unlock( lock );
-        }
+        }
+        unlock( lock );
 }
 
@@ -474 +549 @@
 static inline void lock(spin_queue_lock & this) with(this) {
         mcs_spin_node node;
-        #ifdef __CFA_DEBUG__
-        assert(!(held && owner == active_thread()));
-        #endif
         lock( lock, node );
         while(__atomic_load_n(&held, __ATOMIC_SEQ_CST)) Pause();
         __atomic_store_n(&held, true, __ATOMIC_SEQ_CST);
         unlock( lock, node );
-        #ifdef __CFA_DEBUG__
-        owner = active_thread();
-        #endif
 }
 
 static inline void unlock(spin_queue_lock & this) with(this) {
-        #ifdef __CFA_DEBUG__
-        owner = 0p;
-        #endif
         __atomic_store_n(&held, false, __ATOMIC_RELEASE);
 }
 
-static inline void on_notify(spin_queue_lock & this, struct thread$ * t ) { unpark(t); }
+static inline void on_notify(spin_queue_lock & this, struct thread$ * t ) {
+        unpark(t);
+}
 static inline size_t on_wait(spin_queue_lock & this) { unlock(this); return 0; }
-static inline void on_wakeup(spin_queue_lock & this, size_t recursion ) { }
+static inline void on_wakeup(spin_queue_lock & this, size_t recursion ) {
+        #ifdef REACQ
+        lock(this);
+        #endif
+}
 
 
@@ -511 +583 @@
         // flag showing if lock is held
         volatile bool held;
-
-        #ifdef __CFA_DEBUG__
-        // for deadlock detection
-        struct thread$ * owner;
-        #endif
 };
 
@@ -529 +596 @@
 static inline void lock(mcs_block_spin_lock & this) with(this) {
         mcs_node node;
-        #ifdef __CFA_DEBUG__
-        assert(!(held && owner == active_thread()));
-        #endif
         lock( lock, node );
         while(__atomic_load_n(&held, __ATOMIC_SEQ_CST)) Pause();
         __atomic_store_n(&held, true, __ATOMIC_SEQ_CST);
         unlock( lock, node );
-        #ifdef __CFA_DEBUG__
-        owner = active_thread();
-        #endif
 }
 
 static inline void unlock(mcs_block_spin_lock & this) with(this) {
-        #ifdef __CFA_DEBUG__
-        owner = 0p;
-        #endif
         __atomic_store_n(&held, false, __ATOMIC_SEQ_CST);
 }
@@ -550 +608 @@
 static inline void on_notify(mcs_block_spin_lock & this, struct thread$ * t ) { unpark(t); }
 static inline size_t on_wait(mcs_block_spin_lock & this) { unlock(this); return 0; }
-static inline void on_wakeup(mcs_block_spin_lock & this, size_t recursion ) { }
+static inline void on_wakeup(mcs_block_spin_lock & this, size_t recursion ) {
+        #ifdef REACQ
+        lock(this);
+        #endif
+}
 
 //-----------------------------------------------------------------------------
@@ -565 +627 @@
         // flag showing if lock is held
         volatile bool held;
-
-        #ifdef __CFA_DEBUG__
-        // for deadlock detection
-        struct thread$ * owner;
-        #endif
 };
 
@@ -582 +639 @@
 // if this is called recursively IT WILL DEADLOCK!!!!!
 static inline void lock(block_spin_lock & this) with(this) {
-        #ifdef __CFA_DEBUG__
-        assert(!(held && owner == active_thread()));
-        #endif
         lock( lock );
         while(__atomic_load_n(&held, __ATOMIC_SEQ_CST)) Pause();
         __atomic_store_n(&held, true, __ATOMIC_RELEASE);
         unlock( lock );
+}
+
+static inline void unlock(block_spin_lock & this) with(this) {
+        __atomic_store_n(&held, false, __ATOMIC_RELEASE);
+}
+
+static inline void on_notify(block_spin_lock & this, struct thread$ * t ) with(this.lock) {
+  #ifdef REACQ
+        // first we acquire internal fast_block_lock
+        lock( lock __cfaabi_dbg_ctx2 );
+        if ( held ) { // if internal fast_block_lock is held
+                insert_last( blocked_threads, *t );
+                unlock( lock );
+                return;
+        }
+        // if internal fast_block_lock is not held
+        held = true;
         #ifdef __CFA_DEBUG__
-        owner = active_thread();
-        #endif
-}
-
-static inline void unlock(block_spin_lock & this) with(this) {
-        #ifdef __CFA_DEBUG__
-        owner = 0p;
-        #endif
-        __atomic_store_n(&held, false, __ATOMIC_RELEASE);
-}
-
-static inline void on_notify(block_spin_lock & this, struct thread$ * t ) { unpark(t); }
+        owner = t;
+        #endif
+        unlock( lock );
+
+  #endif
+        unpark(t);
+        
+}
 static inline size_t on_wait(block_spin_lock & this) { unlock(this); return 0; }
-static inline void on_wakeup(block_spin_lock & this, size_t recursion ) { }
+static inline void on_wakeup(block_spin_lock & this, size_t recursion ) with(this) {
+  #ifdef REACQ
+        // now we acquire the entire block_spin_lock upon waking up
+        while(__atomic_load_n(&held, __ATOMIC_SEQ_CST)) Pause();
+        __atomic_store_n(&held, true, __ATOMIC_RELEASE);
+        unlock( lock ); // Now we release the internal fast_spin_lock
+  #endif
+}
 
 //-----------------------------------------------------------------------------