source: src/libcfa/bits/locks.h@ 6dfa2e1

//
// 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.h -- Fast internal locks.
//
// Author           : Thierry Delisle
// Created On       : Tue Oct 31 15:14:38 2017
// Last Modified By : --
// Last Modified On : --
// Update Count     : 0
//

#pragma once

#include "bits/debug.h"
#include "bits/defs.h"

// pause to prevent excess processor bus usage
#if defined( __sparc )
        #define Pause() __asm__ __volatile__ ( "rd %ccr,%g0" )
#elif defined( __i386 ) || defined( __x86_64 )
        #define Pause() __asm__ __volatile__ ( "pause" : : : )
#else
        #error unsupported architecture
#endif

#if defined( __i386 ) || defined( __x86_64 )
        // Intel recommendation
        #define __ALIGN__ __attribute__(( aligned (128) ))
#elif defined( __sparc )
        #define __ALIGN__ CALIGN
#else
        #error unsupported architecture
#endif

#if defined( __x86_64 )
        #define __lock_test_and_test_and_set( lock ) (lock) == 0 && __sync_lock_test_and_set_8( &(lock), 1 ) == 0
        #define __lock_release( lock ) __sync_lock_release_8( &(lock) );
#elif defined( __i386 )
        #define __lock_test_and_test_and_set( lock ) (lock) == 0 && __sync_lock_test_and_set_4( &(lock), 1 ) == 0
        #define __lock_release( lock ) __sync_lock_release_4( &(lock) );
#else
        #error unsupported architecture
#endif

struct __spinlock_t {
        __ALIGN__ volatile uintptr_t lock;
        #ifdef __CFA_DEBUG__
                const char * prev_name;
                void* prev_thrd;
        #endif
} __ALIGN__;

#ifdef __cforall
        extern void yield( unsigned int );
        extern thread_local struct thread_desc *    volatile this_thread;

        static inline void ?{}( __spinlock_t & this ) {
                this.lock = 0;
        }

        // Lock the spinlock, return false if already acquired
        static inline _Bool try_lock  ( __spinlock_t & this __cfaabi_dbg_ctx_param2 ) {
                _Bool result = __lock_test_and_test_and_set( this.lock );
                __cfaabi_dbg_debug_do(
                        if( result ) {
                                this.prev_name = caller;
                                this.prev_thrd = this_thread;
                        }
                )
                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

                for ( unsigned int i = 1;; i += 1 ) {
                        if ( __lock_test_and_test_and_set( this.lock ) ) break;
                        #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_debug_do(
                        this.prev_name = caller;
                        this.prev_thrd = this_thread;
                )
        }

        // Lock the spinlock, spin if already acquired
        static inline void lock_yield( __spinlock_t & this __cfaabi_dbg_ctx_param2 ) {
                for ( unsigned int i = 1;; i += 1 ) {
                        if ( __lock_test_and_test_and_set( this.lock ) ) break;
                        yield( i );
                }
                __cfaabi_dbg_debug_do(
                        this.prev_name = caller;
                        this.prev_thrd = this_thread;
                )
        }

        static inline void unlock( __spinlock_t & this ) {
                __lock_release( this.lock );
        }
#endif