Changeset 5a46e09 for libcfa/src/concurrency

Timestamp:

Jun 29, 2021, 5:33:38 PM (3 years ago)

Author:

caparsons <caparson@…>

Branches:

ADT, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, master, new-ast-unique-expr, pthread-emulation, qualifiedEnum

Children:

660665f

Parents:

bae0d35

Message:

Added Martins SpinCondLock? as linear_backoff_then_block lock

File:

• libcfa/src/concurrency/locks.hfa (modified) (2 diffs)

libcfa/src/concurrency/locks.hfa

@@ -18 +18 @@
 
 #include <stdbool.h>
+#include <stdio.h>
 
 #include "bits/weakso_locks.hfa"
@@ -237 +238 @@
 }
 
+struct linear_backoff_then_block_lock {
+        // Spin lock used for mutual exclusion
+        __spinlock_t spinlock;
+
+        // Current thread owning the lock
+        struct $thread * owner;
+
+        // List of blocked threads
+        dlist( $thread ) blocked_threads;
+
+        // 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 ) {
+        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 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;
+        }
+        return false;
+}
+
+static inline bool try_lock(linear_backoff_then_block_lock & this) { size_t compare_val = 0; return internal_try_lock(this, compare_val); }
+
+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;
+        }
+        return false;
+}
+
+static inline bool block(linear_backoff_then_block_lock & this) with(this) {
+        lock( spinlock __cfaabi_dbg_ctx2 );
+        if (lock_value != 2) {
+                unlock( spinlock );
+                return true;
+        }
+        insert_last( blocked_threads, *active_thread() );
+        unlock( spinlock );
+        park( );
+        return true;
+}
+
+static inline bool lock(linear_backoff_then_block_lock & this) with(this) {
+        // if owner just return
+        if (active_thread() == owner) return true;
+        size_t compare_val = 0;
+        int spin = spin_start;
+        // linear backoff
+        for( ;; ) {
+                compare_val = 0;
+                if (internal_try_lock(this, compare_val)) return true;
+                if (2 == compare_val) break;
+                for (int i = 0; i < spin; i++) Pause();
+                if (spin >= spin_end) break;
+                spin += spin;
+        }
+
+        // linear backoff bounded by spin_count
+        spin = spin_start;
+        int spin_counter = 0;
+        int yield_counter = 0;
+        for ( ;; ) {
+                if(try_lock_contention(this)) return true;
+                if(spin_counter < spin_count) {
+                        for (int i = 0; i < spin; i++) Pause();
+                        if (spin < spin_end) spin += spin;
+                        else spin_counter++;
+                } else if (yield_counter < yield_count) {
+                        // after linear backoff yield yield_count times
+                        yield_counter++;
+                        yield();
+                } else { break; }
+        }
+
+        // block until signalled
+        while (block(this)) if(try_lock_contention(this)) return true;
+        
+        // this should never be reached as block(this) always returns true
+        return false;
+}
+
+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 );
+        $thread * t = &try_pop_front( blocked_threads );
+        unlock( spinlock );
+        unpark( t );
+}
+
+
+void on_notify(linear_backoff_then_block_lock & this, struct $thread * t ) { unpark(t); }
+size_t on_wait(linear_backoff_then_block_lock & this) { unlock(this); return 0; }
+void on_wakeup(linear_backoff_then_block_lock & this, size_t recursion ) { lock(this); }
+
 //-----------------------------------------------------------------------------
 // is_blocking_lock