//
// Cforall Version 1.0.0 Copyright (C) 2019 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// ready_queue.cfa --
//
// Author           : Thierry Delisle
// Created On       : Mon Nov dd 16:29:18 2019
// Last Modified By :
// Last Modified On :
// Update Count     :
//

#define __cforall_thread__

#include "bits/defs.hfa"
#include "kernel_private.hfa"

#define _GNU_SOURCE
#include "stdlib.hfa"

static const size_t cache_line_size = 64;

static inline unsigned __max_processors_fallback() {
	#ifdef __CFA_MAX_PROCESSORS__
		return __CFA_MAX_PROCESSORS__;
	#else
		// No overriden function, no environment variable, no define
		// fall back to a magic number
		return 128;
	#endif
}

__attribute__((weak)) unsigned __max_processors() {
	const char * max_cores_s = getenv("CFA_MAX_PROCESSORS");
	if(!max_cores_s) {
		__cfaabi_dbg_print_nolock("No CFA_MAX_PROCESSORS in ENV");
		return __max_processors_fallback();
	}

	char * endptr = 0p;
	long int max_cores_l = strtol(max_cores_s, &endptr, 10);
	if(max_cores_l < 1 || max_cores_l > 65535) {
		__cfaabi_dbg_print_nolock("CFA_MAX_PROCESSORS out of range : %ld", max_cores_l);
		return __max_processors_fallback();
	}
	if('\0' != *endptr) {
		__cfaabi_dbg_print_nolock("CFA_MAX_PROCESSORS not a decimal number : %s", max_cores_s);
		return __max_processors_fallback();
	}

	return max_cores_l;
}

//=======================================================================
// Cluster wide reader-writer lock
//=======================================================================
void  ?{}(__clusterRWLock_t & this) {
	this.max   = __max_processors();
	this.alloc = 0;
	this.ready = 0;
	this.lock  = false;
	this.data  = alloc(this.max);

	/*paranoid*/ verify( 0 == (((uintptr_t)(this.data    )) % 64) );
	/*paranoid*/ verify( 0 == (((uintptr_t)(this.data + 1)) % 64) );
	/*paranoid*/ verify(__atomic_is_lock_free(sizeof(this.alloc), &this.alloc));
	/*paranoid*/ verify(__atomic_is_lock_free(sizeof(this.ready), &this.ready));

}
void ^?{}(__clusterRWLock_t & this) {
	free(this.data);
}

void ?{}( __processor_id & this, struct processor * proc ) {
	this.handle = proc;
	this.lock   = false;
}

//=======================================================================
// Lock-Free registering/unregistering of threads
unsigned doregister( struct cluster * cltr, struct processor * proc ) with(cltr->ready_lock) {
	// Step - 1 : check if there is already space in the data
	uint_fast32_t s = ready;

	// Check among all the ready
	for(uint_fast32_t i = 0; i < s; i++) {
		processor * null = 0p; // Re-write every loop since compare thrashes it
		if( __atomic_load_n(&data[i].handle, (int)__ATOMIC_RELAXED) == null
			&& __atomic_compare_exchange_n( &data[i].handle, &null, proc, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) {
			/*paranoid*/ verify(i < ready);
			/*paranoid*/ verify(__alignof__(data[i]) == cache_line_size);
			/*paranoid*/ verify((((uintptr_t)&data[i]) % cache_line_size) == 0);
			return i;
		}
	}

	if(max <= alloc) abort("Trying to create more than %ud processors", cltr->ready_lock.max);

	// Step - 2 : F&A to get a new spot in the array.
	uint_fast32_t n = __atomic_fetch_add(&alloc, 1, __ATOMIC_SEQ_CST);
	if(max <= n) abort("Trying to create more than %ud processors", cltr->ready_lock.max);

	// Step - 3 : Mark space as used and then publish it.
	__processor_id * storage = (__processor_id *)&data[n];
	(*storage){ proc };
	while(true) {
		unsigned copy = n;
		if( __atomic_load_n(&ready, __ATOMIC_RELAXED) == n
			&& __atomic_compare_exchange_n(&ready, &copy, n + 1, true, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
			break;
		asm volatile("pause");
	}

	// Return new spot.
	/*paranoid*/ verify(n < ready);
	/*paranoid*/ verify(__alignof__(data[n]) == cache_line_size);
	/*paranoid*/ verify((((uintptr_t)&data[n]) % cache_line_size) == 0);
	return n;
}

void unregister( struct cluster * cltr, struct processor * proc ) with(cltr->ready_lock) {
	unsigned id = proc->id;
	/*paranoid*/ verify(id < ready);
	/*paranoid*/ verify(proc == __atomic_load_n(&data[id].handle, __ATOMIC_RELAXED));
	__atomic_store_n(&data[id].handle, 0p, __ATOMIC_RELEASE);
}

//-----------------------------------------------------------------------
// Writer side : acquire when changing the ready queue, e.g. adding more
//  queues or removing them.
uint_fast32_t ready_mutate_lock( struct cluster & cltr ) with(cltr.ready_lock) {
	// Step 1 : lock global lock
	// It is needed to avoid processors that register mid Critical-Section
	//   to simply lock their own lock and enter.
	__atomic_acquire( &lock );

	// Step 2 : lock per-proc lock
	// Processors that are currently being registered aren't counted
	//   but can't be in read_lock or in the critical section.
	// All other processors are counted
	uint_fast32_t s = ready;
	for(uint_fast32_t i = 0; i < s; i++) {
		__atomic_acquire( &data[i].lock );
	}

	return s;
}

void ready_mutate_unlock( struct cluster & cltr, uint_fast32_t last_s ) with(cltr.ready_lock) {
	// Step 1 : release local locks
	// This must be done while the global lock is held to avoid
	//   threads that where created mid critical section
	//   to race to lock their local locks and have the writer
	//   immidiately unlock them
	// Alternative solution : return s in write_lock and pass it to write_unlock
	for(uint_fast32_t i = 0; i < last_s; i++) {
		verify(data[i].lock);
		__atomic_store_n(&data[i].lock, (bool)false, __ATOMIC_RELEASE);
	}

	// Step 2 : release global lock
	/*paranoid*/ assert(true == lock);
	__atomic_store_n(&lock, (bool)false, __ATOMIC_RELEASE);
}

//=======================================================================
// Intrusive Queue used by ready queue
//=======================================================================
static const size_t fields_offset = offsetof( thread_desc, next );

// Get the head pointer (one before the first element) from the anchor
static inline thread_desc * head(const __intrusive_ready_queue_t & this) {
	thread_desc * rhead = (thread_desc *)(
		(uintptr_t)( &this.before ) - fields_offset
	);
	/* paranoid */ verify(rhead);
	return rhead;
}

// Get the tail pointer (one after the last element) from the anchor
static inline thread_desc * tail(const __intrusive_ready_queue_t & this) {
	thread_desc * rtail = (thread_desc *)(
		(uintptr_t)( &this.after ) - fields_offset
	);
	/* paranoid */ verify(rtail);
	return rtail;
}

// Ctor
void ?{}( __intrusive_ready_queue_t & this ) {
	this.before.prev = 0p;
	this.before.next = tail(this);

	this.after .prev = head(this);
	this.after .next = 0p;

	// We add a boat-load of assertions here because the anchor code is very fragile
	/* paranoid */ verify(((uintptr_t)( head(this) ) + fields_offset) == (uintptr_t)(&this.before));
	/* paranoid */ verify(((uintptr_t)( tail(this) ) + fields_offset) == (uintptr_t)(&this.after ));
	/* paranoid */ verify(head(this)->prev == 0p );
	/* paranoid */ verify(head(this)->next == tail(this) );
	/* paranoid */ verify(tail(this)->next == 0p );
	/* paranoid */ verify(tail(this)->prev == head(this) );
	/* paranoid */ verify(&head(this)->prev == &this.before.prev );
	/* paranoid */ verify(&head(this)->next == &this.before.next );
	/* paranoid */ verify(&tail(this)->prev == &this.after .prev );
	/* paranoid */ verify(&tail(this)->next == &this.after .next );
	/* paranoid */ verify(sizeof(__intrusive_ready_queue_t) == 128);
	/* paranoid */ verify(sizeof(this) == 128);
	/* paranoid */ verify(__alignof__(__intrusive_ready_queue_t) == 128);
	/* paranoid */ verify(__alignof__(this) == 128);
	/* paranoid */ verifyf(((intptr_t)(&this) % 128) == 0, "Expected address to be aligned %p %% 128 == %zd", &this, ((intptr_t)(&this) % 128));
}

// Dtor is trivial
void ^?{}( __intrusive_ready_queue_t & this ) {
	// Make sure the list is empty
	/* paranoid */ verify(head(this)->prev == 0p );
	/* paranoid */ verify(head(this)->next == tail(this) );
	/* paranoid */ verify(tail(this)->next == 0p );
	/* paranoid */ verify(tail(this)->prev == head(this) );
}



bool push(__intrusive_ready_queue_t & this, thread_desc * node) {
	verify(this.lock);
	verify(node->ts != 0);
	verify(node->next == 0p);
	verify(node->prev == 0p);


	// Get the relevant nodes locally
	thread_desc * tail = tail(this);
	thread_desc * prev = tail->prev;

	// Do the push
	node->next = tail;
	node->prev = prev;
	prev->next = node;
	tail->prev = node;

	// Update stats
	#ifndef __CFA_NO_SCHED_STATS__
		this.stat.diff++;
		this.stat.push++;
	#endif

	// Check if the queue used to be empty
	if(this.before.ts == 0l) {
		this.before.ts = node->ts;
		verify(node->prev == head(this));
		return true;
	}
	return false;
}

[thread_desc *, bool] pop(__intrusive_ready_queue_t & this) {
	verify(this.lock);
	thread_desc * head = head(this);
	thread_desc * tail = tail(this);

	thread_desc * node = head->next;
	thread_desc * next = node->next;
	if(node == tail) return [0p, false];

	/* paranoid */ verify(node);

	head->next = next;
	next->prev = head;

	#ifndef __CFA_NO_SCHED_STATS__
		this.stat.diff--;
		this.stat.pop ++;
	#endif

	if(next == tail) {
		this.before.ts = 0ul;
		node->[next, prev] = 0p;
		return [node, true];
	}
	else {
		verify(next->ts != 0);
		this.before.ts = next->ts;
		verify(this.before.ts != 0);
		node->[next, prev] = 0p;
		return [node, false];
	}
}

static inline unsigned long long ts(__intrusive_ready_queue_t & this) {
	return this.before.ts;
}