//
// 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;
	#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;
	}

	// 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;
			#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