source: src/libcfa/bits/locks.h@ 387c9a1

//
// 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 : Peter A. Buhr
// Last Modified On : Fri Mar 30 18:18:13 2018
// Update Count     : 9
//

#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" : : : )
#elif defined( __ARM_ARCH )
        #define Pause() __asm__ __volatile__ ( "nop" : : : )
#else
        #error unsupported architecture
#endif

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

#if __SIZEOF_SIZE_T__ == 8
        #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 __SIZEOF_SIZE_T__ == 4
        #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 size_t lock;
        #ifdef __CFA_DEBUG__
                const char * prev_name;
                void* prev_thrd;
        #endif
} __ALIGN__;

#ifdef __cforall
        extern "C" {
                extern void disable_interrupts();
                extern void enable_interrupts_noPoll();
        }

        extern void yield( unsigned int );

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


        #ifdef __CFA_DEBUG__
                void __cfaabi_dbg_record(__spinlock_t & this, const char * prev_name);
        #else
                #define __cfaabi_dbg_record(x, y)
        #endif

        // 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 );
                if( result ) {
                        disable_interrupts();
                        __cfaabi_dbg_record( this, caller );
                }
                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
                }
                disable_interrupts();
                __cfaabi_dbg_record( this, caller );
        }

        // // Lock the spinlock, yield 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 );
        //      }
        //      disable_interrupts();
        //      __cfaabi_dbg_debug_do(
        //              this.prev_name = caller;
        //              this.prev_thrd = this_thread;
        //      )
        // }

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