source: libcfa/src/bits/locks.hfa @ 9dc0836

//
// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// bits/locks.hfa -- Basic spinlocks that are reused in the system.
// Used for locks that aren't specific to cforall threads and can be used anywhere
//
//  *** Must not contain code specific to libcfathread ***
//
// Author           : Thierry Delisle
// Created On       : Tue Oct 31 15:14:38 2017
// Last Modified By : Peter A. Buhr
// Last Modified On : Wed Aug 12 14:18:07 2020
// Update Count     : 13
//

#pragma once

#include "bits/debug.hfa"
#include "bits/defs.hfa"
#include <assert.h>

struct __spinlock_t {
        // Wrap in struct to prevent false sharing with debug info
        volatile bool lock;
        #ifdef __CFA_DEBUG__
                // previous function to acquire the lock
                const char * prev_name;
                // previous thread to acquire the lock
                void* prev_thrd;
                // keep track of number of times we had to spin, just in case the number is unexpectedly huge
                size_t spin_count;
        #endif
};

#ifdef __cforall
        extern "C" {
                extern void disable_interrupts() OPTIONAL_THREAD;
                extern void enable_interrupts( bool poll = true ) OPTIONAL_THREAD;

                #ifdef __CFA_DEBUG__
                        void __cfaabi_dbg_record_lock(__spinlock_t & this, const char prev_name[]);
                #else
                        #define __cfaabi_dbg_record_lock(x, y)
                #endif
        }

        static inline void ?{}( __spinlock_t & this ) {
                this.lock = 0;
                #ifdef __CFA_DEBUG__
                        this.spin_count = 0;
                #endif
        }

        // Lock the spinlock, return false if already acquired
        static inline bool try_lock  ( __spinlock_t & this __cfaabi_dbg_ctx_param2 ) {
                disable_interrupts();
                bool result = (this.lock == 0) && (__atomic_test_and_set( &this.lock, __ATOMIC_ACQUIRE ) == 0);
                if( result ) {
                        __cfaabi_dbg_record_lock( this, caller );
                } else {
                        enable_interrupts( false );
                }
                return result;
        }

        // Lock the spinlock, spin if already acquired
        static inline void lock( __spinlock_t & this __cfaabi_dbg_ctx_param2 ) {
                #ifndef NOEXPBACK
                        enum { SPIN_START = 4, SPIN_END = 64 * 1024, };
                        unsigned int spin = SPIN_START;
                #endif

                disable_interrupts();
                for ( unsigned int i = 1;; i += 1 ) {
                        if ( (this.lock == 0) && (__atomic_test_and_set( &this.lock, __ATOMIC_ACQUIRE ) == 0) ) break;
                        #ifdef __CFA_DEBUG__
                                this.spin_count++;
                        #endif
                        #ifndef NOEXPBACK
                                // exponential spin
                                for ( volatile unsigned int s = 0; s < spin; s += 1 ) Pause();

                                // slowly increase by powers of 2
                                if ( i % 64 == 0 ) spin += spin;

                                // prevent overflow
                                if ( spin > SPIN_END ) spin = SPIN_START;
                        #else
                                Pause();
                        #endif
                }
                __cfaabi_dbg_record_lock( this, caller );
        }

        static inline void unlock( __spinlock_t & this ) {
                __atomic_clear( &this.lock, __ATOMIC_RELEASE );
                enable_interrupts( false );
        }
#endif