//
// 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__
// #define __CFA_DEBUG_PRINT_READY_QUEUE__

// #define USE_SNZI

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

#define _GNU_SOURCE
#include "stdlib.hfa"
#include "math.hfa"

#include <unistd.h>

#include "snzi.hfa"
#include "ready_subqueue.hfa"

static const size_t cache_line_size = 64;

// No overriden function, no environment variable, no define
// fall back to a magic number
#ifndef __CFA_MAX_PROCESSORS__
	#define __CFA_MAX_PROCESSORS__ 1024
#endif

#define BIAS 16

// returns the maximum number of processors the RWLock support
__attribute__((weak)) unsigned __max_processors() {
	const char * max_cores_s = getenv("CFA_MAX_PROCESSORS");
	if(!max_cores_s) {
		__cfadbg_print_nolock(ready_queue, "No CFA_MAX_PROCESSORS in ENV\n");
		return __CFA_MAX_PROCESSORS__;
	}

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

	return max_cores_l;
}

//=======================================================================
// Cluster wide reader-writer lock
//=======================================================================
void  ?{}(__scheduler_RWLock_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 ^?{}(__scheduler_RWLock_t & this) {
	free(this.data);
}

void ?{}( __scheduler_lock_id_t & this, __processor_id_t * proc ) {
	this.handle = proc;
	this.lock   = false;
	#ifdef __CFA_WITH_VERIFY__
		this.owned  = false;
	#endif
}

//=======================================================================
// Lock-Free registering/unregistering of threads
unsigned doregister( struct __processor_id_t * proc ) with(*__scheduler_lock) {
	__cfadbg_print_safe(ready_queue, "Kernel : Registering proc %p for RW-Lock\n", proc);

	// 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_id_t * 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(0 == (__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", __scheduler_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", __scheduler_lock->max);

	// Step - 3 : Mark space as used and then publish it.
	__scheduler_lock_id_t * storage = (__scheduler_lock_id_t *)&data[n];
	(*storage){ proc };
	while() {
		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;
		Pause();
	}

	__cfadbg_print_safe(ready_queue, "Kernel : Registering proc %p done, id %lu\n", proc, n);

	// Return new spot.
	/*paranoid*/ verify(n < ready);
	/*paranoid*/ verify(__alignof__(data[n]) == (2 * cache_line_size));
	/*paranoid*/ verify((((uintptr_t)&data[n]) % cache_line_size) == 0);
	return n;
}

void unregister( struct __processor_id_t * proc ) with(*__scheduler_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);

	__cfadbg_print_safe(ready_queue, "Kernel : Unregister proc %p\n", proc);
}

//-----------------------------------------------------------------------
// Writer side : acquire when changing the ready queue, e.g. adding more
//  queues or removing them.
uint_fast32_t ready_mutate_lock( void ) with(*__scheduler_lock) {
	/* paranoid */ verify( ! __preemption_enabled() );

	// 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 );
	}

	/* paranoid */ verify( ! __preemption_enabled() );
	return s;
}

void ready_mutate_unlock( uint_fast32_t last_s ) with(*__scheduler_lock) {
	/* paranoid */ verify( ! __preemption_enabled() );

	// 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);

	/* paranoid */ verify( ! __preemption_enabled() );
}

//=======================================================================
// Cforall Reqdy Queue used for scheduling
//=======================================================================
void ?{}(__ready_queue_t & this) with (this) {
	lanes.data  = 0p;
	lanes.count = 0;
}

void ^?{}(__ready_queue_t & this) with (this) {
	verify( 1 == lanes.count );
	#ifdef USE_SNZI
		verify( !query( snzi ) );
	#endif
	free(lanes.data);
}

//-----------------------------------------------------------------------
__attribute__((hot)) bool query(struct cluster * cltr) {
	#ifdef USE_SNZI
		return query(cltr->ready_queue.snzi);
	#endif
	return true;
}

static inline [unsigned, bool] idx_from_r(unsigned r, unsigned preferred) {
	unsigned i;
	bool local;
	#if defined(BIAS)
		unsigned rlow  = r % BIAS;
		unsigned rhigh = r / BIAS;
		if((0 != rlow) && preferred >= 0) {
			// (BIAS - 1) out of BIAS chances
			// Use perferred queues
			i = preferred + (rhigh % 4);
			local = true;
		}
		else {
			// 1 out of BIAS chances
			// Use all queues
			i = rhigh;
			local = false;
		}
	#else
		i = r;
		local = false;
	#endif
	return [i, local];
}

//-----------------------------------------------------------------------
__attribute__((hot)) bool push(struct cluster * cltr, struct $thread * thrd) with (cltr->ready_queue) {
	__cfadbg_print_safe(ready_queue, "Kernel : Pushing %p on cluster %p\n", thrd, cltr);

	// write timestamp
	thrd->link.ts = rdtscl();

	__attribute__((unused)) bool local;
	__attribute__((unused)) int preferred;
	#if defined(BIAS)
		preferred =
			//*
			kernelTLS().this_processor ? kernelTLS().this_processor->id * 4 : -1;
			/*/
			thrd->link.preferred * 4;
			//*/
	#endif

	// Try to pick a lane and lock it
	unsigned i;
	do {
		// Pick the index of a lane
		// unsigned r = __tls_rand();
		unsigned r = __tls_rand_fwd();
		[i, local] = idx_from_r(r, preferred);

		#if !defined(__CFA_NO_STATISTICS__)
			if(local) {
				__tls_stats()->ready.pick.push.local++;
			}
		#endif

		i %= __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );

		#if !defined(__CFA_NO_STATISTICS__)
			__tls_stats()->ready.pick.push.attempt++;
		#endif

		// If we can't lock it retry
	} while( !__atomic_try_acquire( &lanes.data[i].lock ) );

	bool first = false;

	// Actually push it
	#ifdef USE_SNZI
		bool lane_first =
	#endif

	push(lanes.data[i], thrd);

	#ifdef USE_SNZI
		// If this lane used to be empty we need to do more
		if(lane_first) {
			// Check if the entire queue used to be empty
			first = !query(snzi);

			// Update the snzi
			arrive( snzi, i );
		}
	#endif

	__tls_rand_advance_bck();

	// Unlock and return
	__atomic_unlock( &lanes.data[i].lock );

	__cfadbg_print_safe(ready_queue, "Kernel : Pushed %p on cluster %p (idx: %u, mask %llu, first %d)\n", thrd, cltr, i, used.mask[0], lane_first);

	// Update statistics
	#if !defined(__CFA_NO_STATISTICS__)
		#if defined(BIAS)
			if( local ) __tls_stats()->ready.pick.push.lsuccess++;
		#endif
		__tls_stats()->ready.pick.push.success++;
	#endif

	// return whether or not the list was empty before this push
	return first;
}

static struct $thread * try_pop(struct cluster * cltr, unsigned i, unsigned j);
static struct $thread * try_pop(struct cluster * cltr, unsigned i);

// Pop from the ready queue from a given cluster
__attribute__((hot)) $thread * pop(struct cluster * cltr) with (cltr->ready_queue) {
	/* paranoid */ verify( lanes.count > 0 );
	unsigned count = __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );
	int preferred;
	#if defined(BIAS)
		// Don't bother trying locally too much
		int local_tries = 8;
		preferred = kernelTLS().this_processor->id * 4;
	#endif


	// As long as the list is not empty, try finding a lane that isn't empty and pop from it
	#ifdef USE_SNZI
		while( query(snzi) ) {
	#else
		for(25) {
	#endif
		// Pick two lists at random
		// unsigned ri = __tls_rand();
		// unsigned rj = __tls_rand();
		unsigned ri = __tls_rand_bck();
		unsigned rj = __tls_rand_bck();

		unsigned i, j;
		__attribute__((unused)) bool locali, localj;
		[i, locali] = idx_from_r(ri, preferred);
		[j, localj] = idx_from_r(rj, preferred);

		#if !defined(__CFA_NO_STATISTICS__)
			if(locali) {
				__tls_stats()->ready.pick.pop.local++;
			}
			if(localj) {
				__tls_stats()->ready.pick.pop.local++;
			}
		#endif

		i %= count;
		j %= count;

		// try popping from the 2 picked lists
		struct $thread * thrd = try_pop(cltr, i, j);
		if(thrd) {
			#if defined(BIAS) && !defined(__CFA_NO_STATISTICS__)
				if( locali || localj ) __tls_stats()->ready.pick.pop.lsuccess++;
			#endif
			return thrd;
		}
	}

	// All lanes where empty return 0p
	return 0p;
}

__attribute__((hot)) struct $thread * pop_slow(struct cluster * cltr) with (cltr->ready_queue) {
	/* paranoid */ verify( lanes.count > 0 );
	unsigned count = __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );
	unsigned offset = __tls_rand();
	for(i; count) {
		unsigned idx = (offset + i) % count;
		struct $thread * thrd = try_pop(cltr, idx);
		if(thrd) {
			return thrd;
		}
	}

	// All lanes where empty return 0p
	return 0p;
}


//-----------------------------------------------------------------------
// Given 2 indexes, pick the list with the oldest push an try to pop from it
static inline struct $thread * try_pop(struct cluster * cltr, unsigned i, unsigned j) with (cltr->ready_queue) {
	#if !defined(__CFA_NO_STATISTICS__)
		__tls_stats()->ready.pick.pop.attempt++;
	#endif

	// Pick the bet list
	int w = i;
	if( __builtin_expect(!is_empty(lanes.data[j]), true) ) {
		w = (ts(lanes.data[i]) < ts(lanes.data[j])) ? i : j;
	}

	return try_pop(cltr, w);
}

static inline struct $thread * try_pop(struct cluster * cltr, unsigned w) with (cltr->ready_queue) {
	// Get relevant elements locally
	__intrusive_lane_t & lane = lanes.data[w];

	// If list looks empty retry
	if( is_empty(lane) ) return 0p;

	// If we can't get the lock retry
	if( !__atomic_try_acquire(&lane.lock) ) return 0p;


	// If list is empty, unlock and retry
	if( is_empty(lane) ) {
		__atomic_unlock(&lane.lock);
		return 0p;
	}

	// Actually pop the list
	struct $thread * thrd;
	thrd = pop(lane);

	/* paranoid */ verify(thrd);
	/* paranoid */ verify(lane.lock);

	#ifdef USE_SNZI
		// If this was the last element in the lane
		if(emptied) {
			depart( snzi, w );
		}
	#endif

	// Unlock and return
	__atomic_unlock(&lane.lock);

	// Update statistics
	#if !defined(__CFA_NO_STATISTICS__)
		__tls_stats()->ready.pick.pop.success++;
	#endif

	// Update the thread bias
	thrd->link.preferred = w / 4;

	// return the popped thread
	return thrd;
}
//-----------------------------------------------------------------------

bool remove_head(struct cluster * cltr, struct $thread * thrd) with (cltr->ready_queue) {
	for(i; lanes.count) {
		__intrusive_lane_t & lane = lanes.data[i];

		bool removed = false;

		__atomic_acquire(&lane.lock);
			if(head(lane)->link.next == thrd) {
				$thread * pthrd;
				pthrd = pop(lane);

				/* paranoid */ verify( pthrd == thrd );

				removed = true;
				#ifdef USE_SNZI
					if(emptied) {
						depart( snzi, i );
					}
				#endif
			}
		__atomic_unlock(&lane.lock);

		if( removed ) return true;
	}
	return false;
}

//-----------------------------------------------------------------------

static void check( __ready_queue_t & q ) with (q) {
	#if defined(__CFA_WITH_VERIFY__)
		{
			for( idx ; lanes.count ) {
				__intrusive_lane_t & sl = lanes.data[idx];
				assert(!lanes.data[idx].lock);

				assert(head(sl)->link.prev == 0p );
				assert(head(sl)->link.next->link.prev == head(sl) );
				assert(tail(sl)->link.next == 0p );
				assert(tail(sl)->link.prev->link.next == tail(sl) );

				if(sl.before.link.ts == 0l) {
					assert(tail(sl)->link.prev == head(sl));
					assert(head(sl)->link.next == tail(sl));
				} else {
					assert(tail(sl)->link.prev != head(sl));
					assert(head(sl)->link.next != tail(sl));
				}
			}
		}
	#endif
}

// Call this function of the intrusive list was moved using memcpy
// fixes the list so that the pointers back to anchors aren't left dangling
static inline void fix(__intrusive_lane_t & ll) {
	// if the list is not empty then follow he pointer and fix its reverse
	if(!is_empty(ll)) {
		head(ll)->link.next->link.prev = head(ll);
		tail(ll)->link.prev->link.next = tail(ll);
	}
	// Otherwise just reset the list
	else {
		verify(tail(ll)->link.next == 0p);
		tail(ll)->link.prev = head(ll);
		head(ll)->link.next = tail(ll);
		verify(head(ll)->link.prev == 0p);
	}
}

// Grow the ready queue
void ready_queue_grow  (struct cluster * cltr, int target) {
	/* paranoid */ verify( ready_mutate_islocked() );
	__cfadbg_print_safe(ready_queue, "Kernel : Growing ready queue\n");

	// Make sure that everything is consistent
	/* paranoid */ check( cltr->ready_queue );

	// grow the ready queue
	with( cltr->ready_queue ) {
		#ifdef USE_SNZI
			^(snzi){};
		#endif

		// Find new count
		// Make sure we always have atleast 1 list
		size_t ncount = target >= 2 ? target * 4: 1;

		// Allocate new array (uses realloc and memcpies the data)
		lanes.data = alloc( ncount, lanes.data`realloc );

		// Fix the moved data
		for( idx; (size_t)lanes.count ) {
			fix(lanes.data[idx]);
		}

		// Construct new data
		for( idx; (size_t)lanes.count ~ ncount) {
			(lanes.data[idx]){};
		}

		// Update original
		lanes.count = ncount;

		#ifdef USE_SNZI
			// Re-create the snzi
			snzi{ log2( lanes.count / 8 ) };
			for( idx; (size_t)lanes.count ) {
				if( !is_empty(lanes.data[idx]) ) {
					arrive(snzi, idx);
				}
			}
		#endif
	}

	// Make sure that everything is consistent
	/* paranoid */ check( cltr->ready_queue );

	__cfadbg_print_safe(ready_queue, "Kernel : Growing ready queue done\n");

	/* paranoid */ verify( ready_mutate_islocked() );
}

// Shrink the ready queue
void ready_queue_shrink(struct cluster * cltr, int target) {
	/* paranoid */ verify( ready_mutate_islocked() );
	__cfadbg_print_safe(ready_queue, "Kernel : Shrinking ready queue\n");

	// Make sure that everything is consistent
	/* paranoid */ check( cltr->ready_queue );

	with( cltr->ready_queue ) {
		#ifdef USE_SNZI
			^(snzi){};
		#endif

		// Remember old count
		size_t ocount = lanes.count;

		// Find new count
		// Make sure we always have atleast 1 list
		lanes.count = target >= 2 ? target * 4: 1;
		/* paranoid */ verify( ocount >= lanes.count );
		/* paranoid */ verify( lanes.count == target * 4 || target < 2 );

		// for printing count the number of displaced threads
		#if defined(__CFA_DEBUG_PRINT__) || defined(__CFA_DEBUG_PRINT_READY_QUEUE__)
			__attribute__((unused)) size_t displaced = 0;
		#endif

		// redistribute old data
		for( idx; (size_t)lanes.count ~ ocount) {
			// Lock is not strictly needed but makes checking invariants much easier
			__attribute__((unused)) bool locked = __atomic_try_acquire(&lanes.data[idx].lock);
			verify(locked);

			// As long as we can pop from this lane to push the threads somewhere else in the queue
			while(!is_empty(lanes.data[idx])) {
				struct $thread * thrd;
				thrd = pop(lanes.data[idx]);

				push(cltr, thrd);

				// for printing count the number of displaced threads
				#if defined(__CFA_DEBUG_PRINT__) || defined(__CFA_DEBUG_PRINT_READY_QUEUE__)
					displaced++;
				#endif
			}

			// Unlock the lane
			__atomic_unlock(&lanes.data[idx].lock);

			// TODO print the queue statistics here

			^(lanes.data[idx]){};
		}

		__cfadbg_print_safe(ready_queue, "Kernel : Shrinking ready queue displaced %zu threads\n", displaced);

		// Allocate new array (uses realloc and memcpies the data)
		lanes.data = alloc( lanes.count, lanes.data`realloc );

		// Fix the moved data
		for( idx; (size_t)lanes.count ) {
			fix(lanes.data[idx]);
		}

		#ifdef USE_SNZI
			// Re-create the snzi
			snzi{ log2( lanes.count / 8 ) };
			for( idx; (size_t)lanes.count ) {
				if( !is_empty(lanes.data[idx]) ) {
					arrive(snzi, idx);
				}
			}
		#endif
	}

	// Make sure that everything is consistent
	/* paranoid */ check( cltr->ready_queue );

	__cfadbg_print_safe(ready_queue, "Kernel : Shrinking ready queue done\n");
	/* paranoid */ verify( ready_mutate_islocked() );
}