//
// 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__

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

#define _GNU_SOURCE
#include "stdlib.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__ 128
#endif

// 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;
}

// Picks a random 1 bit in 'mask' according to random number 'rnum'.
static inline unsigned rand_bit(unsigned rnum, __cfa_readyQ_mask_t mask) {
#if defined( __i386 )
	static_assert(sizeof(mask) == 4);
	unsigned bit = mask ? rnum % __builtin_popcount(mask) : 0;
	#if !defined(__BMI2__)
		#error rand_bit not implemented for non __BMI2__ i386
	#else
		uint32_t picked = _pdep_u32(1ul << bit, mask);
		return picked ? __builtin_ctz(picked) : 0;
	#endif
#elif defined( __x86_64 )
	static_assert(sizeof(mask) == 8);
	unsigned bit = mask ? rnum % __builtin_popcountl(mask) : 0;
	#if !defined(__BMI2__)
		uint64_t v = mask;   // Input value to find position with rank r.
		unsigned int r = bit + 1;// Input: bit's desired rank [1-64].
		unsigned int s;      // Output: Resulting position of bit with rank r [1-64]
		uint64_t a, b, c, d; // Intermediate temporaries for bit count.
		unsigned int t;      // Bit count temporary.

		// Do a normal parallel bit count for a 64-bit integer,
		// but store all intermediate steps.
		a =  v - ((v >> 1) & ~0UL/3);
		b = (a & ~0UL/5) + ((a >> 2) & ~0UL/5);
		c = (b + (b >> 4)) & ~0UL/0x11;
		d = (c + (c >> 8)) & ~0UL/0x101;


		t = (d >> 32) + (d >> 48);
		// Now do branchless select!
		s  = 64;
		s -= ((t - r) & 256) >> 3; r -= (t & ((t - r) >> 8));
		t  = (d >> (s - 16)) & 0xff;
		s -= ((t - r) & 256) >> 4; r -= (t & ((t - r) >> 8));
		t  = (c >> (s - 8)) & 0xf;
		s -= ((t - r) & 256) >> 5; r -= (t & ((t - r) >> 8));
		t  = (b >> (s - 4)) & 0x7;
		s -= ((t - r) & 256) >> 6; r -= (t & ((t - r) >> 8));
		t  = (a >> (s - 2)) & 0x3;
		s -= ((t - r) & 256) >> 7; r -= (t & ((t - r) >> 8));
		t  = (v >> (s - 1)) & 0x1;
		s -= ((t - r) & 256) >> 8;
		return s - 1;
	#else
		uint64_t picked = _pdep_u64(1ul << bit, mask);
		return picked ? __builtin_ctzl(picked) : 0;
	#endif
#elif defined( __ARM_ARCH )
	#error rand_bit not implemented for arm
#else
	#error uknown hardware architecture
#endif
}


//-----------------------------------------------------------------------------
// Helpers used by extract
// (_mask_bitsidx() & X) returns a bit index valid for a __cfa_readyQ_mask_t, where X is any integer
static inline __cfa_readyQ_mask_t _mask_bitsidx () __attribute__ ((const)) { return (8 * sizeof(__cfa_readyQ_mask_t)) - 1; }

// (X >> _mask_shiftidx()) retuns an index into an array of __cfa_readyQ_mask_t
static inline __cfa_readyQ_mask_t _mask_shiftidx() __attribute__ ((const)) { return (8 * sizeof(__cfa_readyQ_mask_t)) - __builtin_clzl(_mask_bitsidx()); }


// Assuming a large bit mask represented as an array of __cfa_readyQ_mask_t
// Given an index into the large mask, returns the bit index and which __cfa_readyQ_mask_t index in the array
static inline [__cfa_readyQ_mask_t, __cfa_readyQ_mask_t] extract(__cfa_readyQ_mask_t idx) {
	__cfa_readyQ_mask_t word = idx >> _mask_shiftidx();
	__cfa_readyQ_mask_t bit  = idx &  _mask_bitsidx();
	return [bit, word];
}

//=======================================================================
// 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 doregister2( struct cluster * cltr, struct processor * proc ) with(cltr->ready_lock) {
	__cfadbg_print_safe(ready_queue, "Kernel : Registering proc %p with cluster %p\n", proc, cltr);

	// 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");
	}

	__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]) == cache_line_size);
	/*paranoid*/ verify((((uintptr_t)&data[n]) % cache_line_size) == 0);
	return n;
}

void unregister2( 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);

	__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( 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
//=======================================================================
// Get the head pointer (one before the first element) from the anchor
static inline $thread * head(const __intrusive_lane_t & this) {
	$thread * rhead = ($thread *)(
		(uintptr_t)( &this.before ) - offsetof( $thread, link )
	);
	/* paranoid */ verify(rhead);
	return rhead;
}

// Get the tail pointer (one after the last element) from the anchor
static inline $thread * tail(const __intrusive_lane_t & this) {
	$thread * rtail = ($thread *)(
		(uintptr_t)( &this.after ) - offsetof( $thread, link )
	);
	/* paranoid */ verify(rtail);
	return rtail;
}

// Ctor
void ?{}( __intrusive_lane_t & this ) {
	this.lock = false;
	#if defined(__CFA_WITH_VERIFY__)
		this.last_id = -1u;
		this.count = 0u;
	#endif

	this.before.link.prev = 0p;
	this.before.link.next = tail(this);
	this.before.link.ts   = 0;

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

	#if !defined(__CFA_NO_SCHED_STATS__)
		this.stat.diff = 0;
		this.stat.push = 0;
		this.stat.pop  = 0;
	#endif

	// We add a boat-load of assertions here because the anchor code is very fragile
	/* paranoid */ verify(((uintptr_t)( head(this) ) + offsetof( $thread, link )) == (uintptr_t)(&this.before));
	/* paranoid */ verify(((uintptr_t)( tail(this) ) + offsetof( $thread, link )) == (uintptr_t)(&this.after ));
	/* paranoid */ verify(head(this)->link.prev == 0p );
	/* paranoid */ verify(head(this)->link.next == tail(this) );
	/* paranoid */ verify(tail(this)->link.next == 0p );
	/* paranoid */ verify(tail(this)->link.prev == head(this) );
	/* paranoid */ verify(&head(this)->link.prev == &this.before.link.prev );
	/* paranoid */ verify(&head(this)->link.next == &this.before.link.next );
	/* paranoid */ verify(&tail(this)->link.prev == &this.after .link.prev );
	/* paranoid */ verify(&tail(this)->link.next == &this.after .link.next );
	/* paranoid */ verify(sizeof(__intrusive_lane_t) == 128);
	/* paranoid */ verify(sizeof(this) == 128);
	/* paranoid */ verify(__alignof__(__intrusive_lane_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));

	/* paranoid */ verifyf(_mask_shiftidx() == 6 , "%llu", _mask_shiftidx());
	/* paranoid */ verifyf(_mask_bitsidx () == 63, "%llu", _mask_bitsidx());
}

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

// Push a thread onto this lane
// returns true of lane was empty before push, false otherwise
bool push(__intrusive_lane_t & this, $thread * node) {
	#if defined(__CFA_WITH_VERIFY__)
		/* paranoid */ verify(this.lock);
		/* paranoid */ verify(node->link.ts != 0);
		/* paranoid */ verify(node->link.next == 0p);
		/* paranoid */ verify(node->link.prev == 0p);
		/* paranoid */ verify(tail(this)->link.next == 0p);
		/* paranoid */ verify(head(this)->link.prev == 0p);

		this.count++;

		if(this.before.link.ts == 0l) {
			/* paranoid */ verify(tail(this)->link.prev == head(this));
			/* paranoid */ verify(head(this)->link.next == tail(this));
		} else {
			/* paranoid */ verify(tail(this)->link.prev != head(this));
			/* paranoid */ verify(head(this)->link.next != tail(this));
		}
	#endif

	// Get the relevant nodes locally
	$thread * tail = tail(this);
	$thread * prev = tail->link.prev;

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

	// Update stats
	#if !defined(__CFA_NO_SCHED_STATS__)
		this.stat.diff++;
		this.stat.push++;
	#endif

	verify(node->link.next == tail(this));

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

// Pop a thread from this lane (must be non-empty)
// returns popped
// returns true of lane was empty before push, false otherwise
[$thread *, bool] pop(__intrusive_lane_t & this) {
	/* paranoid */ verify(this.lock);
	/* paranoid */ verify(this.before.link.ts != 0ul);

	// Get anchors locally
	$thread * head = head(this);
	$thread * tail = tail(this);

	// Get the relevant nodes locally
	$thread * node = head->link.next;
	$thread * next = node->link.next;

	#if defined(__CFA_WITH_VERIFY__)
		this.count--;
		/* paranoid */ verify(node != tail);
		/* paranoid */ verify(node);
	#endif

	// Do the pop
	head->link.next = next;
	next->link.prev = head;
	node->link.[next, prev] = 0p;

	// Update head time stamp
	this.before.link.ts = next->link.ts;

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

	// Check if we emptied list and return accordingly
	/* paranoid */ verify(tail(this)->link.next == 0p);
	/* paranoid */ verify(head(this)->link.prev == 0p);
	if(next == tail) {
		/* paranoid */ verify(this.before.link.ts == 0);
		/* paranoid */ verify(tail(this)->link.prev == head(this));
		/* paranoid */ verify(head(this)->link.next == tail(this));
		return [node, true];
	}
	else {
		/* paranoid */ verify(next->link.ts != 0);
		/* paranoid */ verify(tail(this)->link.prev != head(this));
		/* paranoid */ verify(head(this)->link.next != tail(this));
		/* paranoid */ verify(this.before.link.ts != 0);
		return [node, false];
	}
}

// Check whether or not list is empty
static inline bool is_empty(__intrusive_lane_t & this) {
	// Cannot verify here since it may not be locked
	return this.before.link.ts == 0;
}

// Return the timestamp
static inline unsigned long long ts(__intrusive_lane_t & this) {
	// Cannot verify here since it may not be locked
	return this.before.link.ts;
}

//=======================================================================
// Cforall Reqdy Queue used by ready queue
//=======================================================================

// Thread local mirror of ready queue statistics
#if !defined(__CFA_NO_STATISTICS__)
static __attribute__((aligned(128))) thread_local struct {
	struct {
		struct {
			size_t attempt;
			size_t success;
		} push;
		struct {
			size_t maskrds;
			size_t attempt;
			size_t success;
		} pop;
	} pick;
	struct {
		size_t value;
		size_t count;
	} used;
} tls = {
	/* pick */{
		/* push */{ 0, 0 },
		/* pop  */{ 0, 0, 0 },
	},
	/* used */{ 0, 0 }
};
#endif

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

void ?{}(__ready_queue_t & this) with (this) {
	used.count = 0;
	for( i ; __cfa_lane_mask_size ) {
		used.mask[i] = 0;
	}

	lanes.data = alloc(4);
	for( i; 4 ) {
		(lanes.data[i]){};
	}
	lanes.count = 4;

	#if !defined(__CFA_NO_STATISTICS__)
		global_stats.pick.push.attempt = 0;
		global_stats.pick.push.success = 0;
		global_stats.pick.pop .maskrds = 0;
		global_stats.pick.pop .attempt = 0;
		global_stats.pick.pop .success = 0;

		global_stats.used.value = 0;
		global_stats.used.count = 0;
	#endif
}

void ^?{}(__ready_queue_t & this) with (this) {
	verify( 4  == lanes.count );
	verify( 0  == used .count );

	for( i; 4 ) {
		^(lanes.data[i]){};
	}
	free(lanes.data);


	#if defined(__CFA_WITH_VERIFY__)
		for( i ; __cfa_lane_mask_size ) {
			assert( 0 == used.mask[i] );
		}
	#endif
}

//-----------------------------------------------------------------------
enum mask_strictness {
	STRICT,
	NOCHECK
};

// Set a given bit in the bit mask array
// strictness determines of the bit had to be cleared before
static inline void mask_set(__cfa_readyQ_mask_t * mask, unsigned index, mask_strictness strict) {
	// Extract the array and bit indexes
	__cfa_readyQ_mask_t word;
	__cfa_readyQ_mask_t bit;
	[bit, word] = extract(index);

	__cfadbg_print_safe(ready_queue, "Kernel : Ready queue extracted index %u as [bit %llu, word %llu]\n", index, bit, word);

	// Conditional check
	verifyf(
		strict != STRICT || // Conditional check if it was expected to be cleared
		((mask[word] & (1ull << bit)) == 0),
		"Before set %llu:%llu (%u), %llx & %llx", word, bit, index, mask[word], (1ull << bit)
	);

	// Atomically set the bit
	__attribute__((unused)) bool ret = __atomic_bts(&mask[word], bit);

	// Conditional check
	verifyf(
		strict != STRICT || // Conditional check if it was expected to be cleared
		!ret,
		"Bit was not set but bts returned true"
	);

	// Unconditional check
	verifyf(
		(mask[word] & (1ull << bit)) != 0,
		"After set %llu:%llu (%u), %llx & %llx", word, bit, index, mask[word], (1ull << bit)
	);
}

static inline void mask_clear(__cfa_readyQ_mask_t * mask, unsigned index, mask_strictness strict) {
	// Extract the array and bit indexes
	__cfa_readyQ_mask_t word;
	__cfa_readyQ_mask_t bit;
	[bit, word] = extract(index);

	// Conditional check
	verifyf(
		strict != STRICT || // Conditional check if it was expected to be set
		((mask[word] & (1ull << bit)) != 0),
		"Before clear %llu:%llu (%u), %llx & %llx", word, bit, index, mask[word], (1ull << bit)
	);

	// Atomically clear the bit
	__attribute__((unused)) bool ret = __atomic_btr(&mask[word], bit);

	// Conditional check
	verifyf(
		strict != STRICT || // Conditional check if it was expected to be cleared
		ret,
		"Bit was set but btr returned false"
	);

	// Unconditional check
	verifyf(
		(mask[word] & (1ull << bit)) == 0,
		"After clear %llu:%llu (%u), %llx & %llx", word, bit, index, mask[word], (1ull << bit)
	);
}

//-----------------------------------------------------------------------
__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 (mask %llu)\n", thrd, cltr, used.mask[0]);

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

	// Try to pick a lane and lock it
	unsigned i;
	do {
		// Pick the index of a lane
		i = __tls_rand() % lanes.count;

		#if !defined(__CFA_NO_STATISTICS__)
			tls.pick.push.attempt++;
		#endif

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

	#if defined(__CFA_WITH_VERIFY__)
		/* paranoid */ verify(lanes.data[i].last_id == -1u);
		/* paranoid */ lanes.data[i].last_id = kernelTLS.this_processor->id;
	#endif

	__attribute__((unused)) size_t num = __atomic_load_n( &used.count, __ATOMIC_RELAXED );
	bool first = false;

	// Actually push it
	bool lane_first = push(lanes.data[i], thrd);

	// If this lane used to be empty we need to do more
	if(lane_first) {
		// Update the bit mask
		mask_set((__cfa_readyQ_mask_t *)used.mask, i, STRICT);

		// Update the global count
		size_t ret = __atomic_fetch_add( &used.count, 1z, __ATOMIC_SEQ_CST);

		// Check if the entire queue used to be empty
		first = (ret == 0);
	}

	#if defined(__CFA_WITH_VERIFY__)
		/* paranoid */ verifyf( used.count <= lanes.count, "Non-empty count (%zu) exceeds actual count (%zu)\n", used.count, lanes.count );
		/* paranoid */ verifyf( lanes.data[i].last_id == kernelTLS.this_processor->id, "Expected last processor to lock queue %u to be %u, was %u\n", i, lanes.data[i].last_id, kernelTLS.this_processor->id );
		/* paranoid */ verifyf( lanes.data[i].lock, "List %u is not locked\n", i );
		/* paranoid */ lanes.data[i].last_id = -1u;
	#endif

	// 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__)
		tls.pick.push.success++;
		tls.used.value += num;
		tls.used.count += 1;
	#endif

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

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

	// 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 defined(__CFA_WITH_VERIFY__)
		/* paranoid */ verify(lane.last_id == -1u);
		/* paranoid */ lane.last_id = kernelTLS.this_processor->id;
	#endif


	// If list is empty, unlock and retry
	if( is_empty(lane) ) {
		#if defined(__CFA_WITH_VERIFY__)
			/* paranoid */ verify(lane.last_id == kernelTLS.this_processor->id);
			/* paranoid */ lane.last_id = -1u;
		#endif

		__atomic_unlock(&lane.lock);
		return 0p;
	}

	// Actually pop the list
	struct $thread * thrd;
	bool emptied;
	[thrd, emptied] = pop(lane);

	/* paranoid */ verify(thrd);
	/* paranoid */ verify(lane.last_id == kernelTLS.this_processor->id);
	/* paranoid */ verify(lane.lock);

	// If this was the last element in the lane
	if(emptied) {
		// Update the global count
		__atomic_fetch_sub( &used.count, 1z, __ATOMIC_SEQ_CST);

		// Update the bit mask
		mask_clear((__cfa_readyQ_mask_t *)used.mask, w, STRICT);
	}

	#if defined(__CFA_WITH_VERIFY__)
		/* paranoid */ verify(lane.last_id == kernelTLS.this_processor->id);
		/* paranoid */ lane.last_id = -1u;
	#endif

	// For statistics, check the count before we release the lock
	#if !defined(__CFA_NO_STATISTICS__)
		int num = __atomic_load_n( &used.count, __ATOMIC_RELAXED );
	#endif

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

	// Update statistics
	#if !defined(__CFA_NO_STATISTICS__)
		tls.pick.pop.success++;
		tls.used.value += num;
		tls.used.count += 1;
	#endif

	// return the popped thread
	return thrd;
}

// 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 );

	// As long as the list is not empty, try finding a lane that isn't empty and pop from it
	while( __atomic_load_n( &used.count, __ATOMIC_RELAXED ) != 0) {
		#if !defined(__CFA_READQ_NO_BITMASK__)
			// If using bit masks
			#if !defined(__CFA_NO_SCHED_STATS__)
				tls.pick.pop.maskrds++;
			#endif

			// Pick two lists at random
			unsigned ri = __tls_rand();
			unsigned rj = __tls_rand();

			// Find which __cfa_readyQ_mask_t the two lists belong
			unsigned num = ((__atomic_load_n( &lanes.count, __ATOMIC_RELAXED ) - 1) >> 6) + 1;
			unsigned wdxi = (ri >> 6u) % num;
			unsigned wdxj = (rj >> 6u) % num;

			// Get the actual __cfa_readyQ_mask_t
			size_t maski = __atomic_load_n( &used.mask[wdxi], __ATOMIC_RELAXED );
			size_t maskj = __atomic_load_n( &used.mask[wdxj], __ATOMIC_RELAXED );

			// If both of these masks are empty, retry
			if(maski == 0 && maskj == 0) continue;

			// Pick one of the non-zero bits in the masks and get the bit indexes
			unsigned bi = rand_bit(ri, maski);
			unsigned bj = rand_bit(rj, maskj);

			// some checks
			/* paranoid */ verifyf(bi < 64, "%zu %u", maski, bi);
			/* paranoid */ verifyf(bj < 64, "%zu %u", maskj, bj);

			// get the general list index
			unsigned i = bi | (wdxi << 6);
			unsigned j = bj | (wdxj << 6);

			// some more checks
			/* paranoid */ verifyf(i < lanes.count, "%u", wdxi << 6);
			/* paranoid */ verifyf(j < lanes.count, "%u", wdxj << 6);

			// try popping from the 2 picked lists
			struct $thread * thrd = try_pop(cltr, i, j);
			if(thrd) return thrd;
		#else
			// Pick two lists at random
			int i = __tls_rand() % __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );
			int j = __tls_rand() % __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );

			// try popping from the 2 picked lists
			struct $thread * thrd = try_pop(cltr, i, j);
			if(thrd) return thrd;
		#endif
	}

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

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

static void check( __ready_queue_t & q ) with (q) {
	#if defined(__CFA_WITH_VERIFY__)
		{
			int idx = 0;
			for( w ; __cfa_lane_mask_size ) {
				for( b ; 8 * sizeof(__cfa_readyQ_mask_t) ) {
					bool is_empty = idx < lanes.count ? (ts(lanes.data[idx]) == 0) : true;
					bool should_be_empty = 0 == (used.mask[w] & (1z << b));
					assertf(should_be_empty == is_empty, "Inconsistent list %d, mask expect : %d, actual is got %d", idx, should_be_empty, (bool)is_empty);
					assert(__cfa_max_lanes > idx);
					idx++;
				}
			}
		}

		{
			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) {
	// Lock the RWlock so no-one pushes/pops while we are changing the queue
	uint_fast32_t last_size = ready_mutate_lock( *cltr );

	__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 ) {
		size_t ncount = lanes.count;

		// Check that we have some space left
		if(ncount + 4 >= __cfa_max_lanes) abort("Program attempted to create more than maximum number of Ready Queues (%zu)", __cfa_max_lanes);

		// increase count
		ncount += 4;

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

		// 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;

		// fields in 'used' don't need to change when growing
	}

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

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

	// Unlock the RWlock
	ready_mutate_unlock( *cltr, last_size );
}

// Shrink the ready queue
void ready_queue_shrink(struct cluster * cltr) {
	// Lock the RWlock so no-one pushes/pops while we are changing the queue
	uint_fast32_t last_size = ready_mutate_lock( *cltr );

	__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 ) {
		// Make sure that the total thread count stays the same
		#if defined(__CFA_WITH_VERIFY__)
			size_t nthreads = 0;
			for( idx; (size_t)lanes.count ) {
				nthreads += lanes.data[idx].count;
			}
		#endif

		size_t ocount = lanes.count;
		// Check that we have some space left
		if(ocount < 8) abort("Program attempted to destroy more Ready Queues than were created");

		// reduce the actual count so push doesn't use the old queues
		lanes.count -= 4;
		verify(ocount > lanes.count);

		// 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;
				__attribute__((unused)) bool _;
				[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
			}

			mask_clear((__cfa_readyQ_mask_t *)used.mask, idx, NOCHECK);

			// 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);

		// recompute the used.count instead of maintaining it
		used.count = 0;
		for( i ; __cfa_lane_mask_size ) {
			used.count += __builtin_popcountl(used.mask[i]);
		}

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

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

		// Make sure that the total thread count stayed the same
		#if defined(__CFA_WITH_VERIFY__)
			for( idx; (size_t)lanes.count ) {
				nthreads -= lanes.data[idx].count;
			}
			verifyf(nthreads == 0, "Shrinking changed number of threads");
		#endif
	}

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

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

	// Unlock the RWlock
	ready_mutate_unlock( *cltr, last_size );
}

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

#if !defined(__CFA_NO_STATISTICS__)
void stats_tls_tally(struct cluster * cltr) with (cltr->ready_queue) {
	__atomic_fetch_add( &global_stats.pick.push.attempt, tls.pick.push.attempt, __ATOMIC_SEQ_CST );
	__atomic_fetch_add( &global_stats.pick.push.success, tls.pick.push.success, __ATOMIC_SEQ_CST );
	__atomic_fetch_add( &global_stats.pick.pop .maskrds, tls.pick.pop .maskrds, __ATOMIC_SEQ_CST );
	__atomic_fetch_add( &global_stats.pick.pop .attempt, tls.pick.pop .attempt, __ATOMIC_SEQ_CST );
	__atomic_fetch_add( &global_stats.pick.pop .success, tls.pick.pop .success, __ATOMIC_SEQ_CST );

	__atomic_fetch_add( &global_stats.used.value, tls.used.value, __ATOMIC_SEQ_CST );
	__atomic_fetch_add( &global_stats.used.count, tls.used.count, __ATOMIC_SEQ_CST );
}
#endif