//
// 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;
}

static inline unsigned rand_bit(unsigned rnum, size_t mask) {
	verify(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
}

static inline __cfa_readyQ_mask_t readyQ_mask_full       () { return (8 * sizeof(__cfa_readyQ_mask_t)) - 1; }
static inline __cfa_readyQ_mask_t readyQ_mask_shit_length() { return (8 * sizeof(__cfa_readyQ_mask_t)) - __builtin_clzl(readyQ_mask_full()); }

static inline [__cfa_readyQ_mask_t, __cfa_readyQ_mask_t] extract(__cfa_readyQ_mask_t idx) {
	__cfa_readyQ_mask_t word = idx >> readyQ_mask_shit_length();
	__cfa_readyQ_mask_t bit  = idx &  readyQ_mask_full();
	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 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
//=======================================================================
// 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 ) - offsetof( thread_desc, link )
	);
	/* 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 ) - offsetof( thread_desc, link )
	);
	/* paranoid */ verify(rtail);
	return rtail;
}

// Ctor
void ?{}( __intrusive_ready_queue_t & this ) {
	this.lock = false;
	this.last_id = -1u;

	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_desc, link )) == (uintptr_t)(&this.before));
	/* paranoid */ verify(((uintptr_t)( tail(this) ) + offsetof( thread_desc, 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_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));

	/* paranoid */ verifyf(readyQ_mask_shit_length() == 6 , "%zu", readyQ_mask_shit_length());
	/* paranoid */ verifyf(readyQ_mask_full()        == 63, "%zu", readyQ_mask_full());
}

// Dtor is trivial
void ^?{}( __intrusive_ready_queue_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) );
}



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

	if(this.before.link.ts == 0l) {
		verify(tail(this)->link.next == 0p);
		verify(tail(this)->link.prev == head(this));
		verify(head(this)->link.next == tail(this));
		verify(head(this)->link.prev == 0p);
	}

	// Get the relevant nodes locally
	thread_desc * tail = tail(this);
	thread_desc * 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
	#ifndef __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;
		verify(node->link.prev == head(this));
		return true;
	}
	return false;
}

[thread_desc *, bool] pop(__intrusive_ready_queue_t & this) {
	verify(this.lock);
	verify(this.before.link.ts != 0ul);
	thread_desc * head = head(this);
	thread_desc * tail = tail(this);

	thread_desc * node = head->link.next;
	thread_desc * next = node->link.next;
	if(node == tail) {
		verify(false);
		verify(this.before.link.ts == 0ul);
		verify(tail(this)->link.next == 0p);
		verify(tail(this)->link.prev == head(this));
		verify(head(this)->link.next == tail(this));
		verify(head(this)->link.prev == 0p);
		return [0p, false];
	}

	/* paranoid */ verify(node);

	head->link.next = next;
	next->link.prev = head;

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

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

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

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

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;
	} full;
} tls = {
	/* pick */{
		/* push */{ 0, 0 },
		/* pop  */{ 0, 0, 0 },
	},
	/* full */{ 0, 0 }
};

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

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

	list.data = alloc(4);
	for( i; 4 ) {
		(list.data[i]){};
	}
	list.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.full.value = 0;
		global_stats.full.count = 0;
	#endif
}

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

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


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

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

__attribute__((hot)) bool push(struct cluster * cltr, struct thread_desc * thrd) with (cltr->ready_queue) {
	thrd->link.ts = rdtscl();

	while(true) {
		// Pick a random list
		unsigned i = tls_rand() % list.count;

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

		// If we can't lock it retry
		if( !__atomic_try_acquire( &list.data[i].lock ) ) continue;
		verify(list.data[i].last_id == -1u);
		list.data[i].last_id = kernelTLS.this_processor->id;

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

		verify( list.data[i].last_id == kernelTLS.this_processor->id );
		verify( list.data[i].lock );
		// Actually push it
		if(push(list.data[i], thrd)) {
			size_t ret = __atomic_fetch_add( &empty.count, 1z, __ATOMIC_SEQ_CST);
			first = (ret == 0);

			__cfa_readyQ_mask_t word;
			__cfa_readyQ_mask_t bit;
			[bit, word] = extract(i);
			verifyf((empty.mask[word] & (1ull << bit)) == 0, "Before set %llu:%llu (%u), %llx & %llx", word, bit, i, empty.mask[word], (1ull << bit));
			__attribute__((unused)) bool ret = bts(&empty.mask[word], bit);
			verify(!(bool)ret);
			verifyf((empty.mask[word] & (1ull << bit)) != 0, "After set %llu:%llu (%u), %llx & %llx", word, bit, i, empty.mask[word], (1ull << bit));
		}
		verify(empty.count <= (int)list.count);
		verify( list.data[i].last_id == kernelTLS.this_processor->id );
		verify( list.data[i].lock );

		// Unlock and return
		list.data[i].last_id = -1u;
		__atomic_unlock( &list.data[i].lock );

		#if !defined(__CFA_NO_STATISTICS__)
			tls.pick.push.success++;
			tls.full.value += num;
			tls.full.count += 1;
		#endif
		return first;
	}
}

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

static struct thread_desc * 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(ts(list.data[j]) != 0, true) ) {
		w = (ts(list.data[i]) < ts(list.data[j])) ? i : j;
	}

	__intrusive_ready_queue_t & list = list.data[w];
	// If list looks empty retry
	if( ts(list) == 0 ) return 0p;

	// If we can't get the lock retry
	if( !__atomic_try_acquire(&list.lock) ) return 0p;
	verify(list.last_id == -1u);
	list.last_id = kernelTLS.this_processor->id;

	verify(list.last_id == kernelTLS.this_processor->id);

	__attribute__((unused)) int num = __atomic_load_n( &empty.count, __ATOMIC_RELAXED );


	// If list is empty, unlock and retry
	if( ts(list) == 0 ) {
		list.last_id = -1u;
		__atomic_unlock(&list.lock);
		return 0p;
	}
	{
		__cfa_readyQ_mask_t word;
		__cfa_readyQ_mask_t bit;
		[bit, word] = extract(w);
		verify((empty.mask[word] & (1ull << bit)) != 0);
	}

	verify(list.last_id == kernelTLS.this_processor->id);
	verify(list.lock);

	// Actually pop the list
	struct thread_desc * thrd;
	bool emptied;
	[thrd, emptied] = pop(list);
	verify(thrd);

	verify(list.last_id == kernelTLS.this_processor->id);
	verify(list.lock);

	if(emptied) {
		__atomic_fetch_sub( &empty.count, 1z, __ATOMIC_SEQ_CST);

		__cfa_readyQ_mask_t word;
		__cfa_readyQ_mask_t bit;
		[bit, word] = extract(w);
		verify((empty.mask[word] & (1ull << bit)) != 0);
		__attribute__((unused)) bool ret = btr(&empty.mask[word], bit);
		verify(ret);
		verify((empty.mask[word] & (1ull << bit)) == 0);
	}

	verify(list.lock);

	// Unlock and return
	list.last_id = -1u;
	__atomic_unlock(&list.lock);
	verify(empty.count >= 0);

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

	return thrd;
}

__attribute__((hot)) thread_desc * pop(struct cluster * cltr) with (cltr->ready_queue) {
	verify( list.count > 0 );
	while( __atomic_load_n( &empty.count, __ATOMIC_RELAXED ) != 0) {
		#if !defined(__CFA_READQ_NO_BITMASK__)
			tls.pick.pop.maskrds++;
			unsigned i, j;
			{
				#if !defined(__CFA_NO_SCHED_STATS__)
					tls.pick.pop.maskrds++;
				#endif

				// Pick two lists at random
				unsigned num = ((__atomic_load_n( &list.count, __ATOMIC_RELAXED ) - 1) >> 6) + 1;

				unsigned ri = tls_rand();
				unsigned rj = tls_rand();

				unsigned wdxi = (ri >> 6u) % num;
				unsigned wdxj = (rj >> 6u) % num;

				size_t maski = __atomic_load_n( &empty.mask[wdxi], __ATOMIC_RELAXED );
				size_t maskj = __atomic_load_n( &empty.mask[wdxj], __ATOMIC_RELAXED );

				if(maski == 0 && maskj == 0) continue;

				unsigned bi = rand_bit(ri, maski);
				unsigned bj = rand_bit(rj, maskj);

				verifyf(bi < 64, "%zu %u", maski, bi);
				verifyf(bj < 64, "%zu %u", maskj, bj);

				i = bi | (wdxi << 6);
				j = bj | (wdxj << 6);

				verifyf(i < list.count, "%u", wdxi << 6);
				verifyf(j < list.count, "%u", wdxj << 6);
			}

			struct thread_desc * thrd = try_pop(cltr, i, j);
			if(thrd) return thrd;
		#else
			// Pick two lists at random
			int i = tls_rand() % __atomic_load_n( &list.count, __ATOMIC_RELAXED );
			int j = tls_rand() % __atomic_load_n( &list.count, __ATOMIC_RELAXED );

			struct thread_desc * thrd = try_pop(cltr, i, j);
			if(thrd) return thrd;
		#endif
	}

	return 0p;
}

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

static void check( __ready_queue_t & q ) with (q) {
	#if defined(__CFA_WITH_VERIFY__)
		{
			int idx = 0;
			for( w ; __cfa_readyQ_mask_size ) {
				for( b ; 8 * sizeof(__cfa_readyQ_mask_t) ) {
					bool is_empty = idx < list.count ? (ts(list.data[idx]) == 0) : true;
					bool should_be_empty = 0 == (empty.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_readyQs > idx);
					idx++;
				}
			}
		}

		{
			for( idx ; list.count ) {
				__intrusive_ready_queue_t & sl = list.data[idx];
				assert(!list.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.next == 0p);
					assert(tail(sl)->link.prev == head(sl));
					assert(head(sl)->link.next == tail(sl));
					assert(head(sl)->link.prev == 0p);
				}
			}
		}
	#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_ready_queue_t & ll) {
	// if the list is not empty then follow he pointer
	// and fix its reverse
	if(ll.before.link.ts != 0l) {
		head(ll)->link.next->link.prev = head(ll);
		tail(ll)->link.prev->link.next = tail(ll);
	}
	// Otherwise just reset the list
	else {
		tail(ll)->link.next = 0p;
		tail(ll)->link.prev = head(ll);
		head(ll)->link.next = tail(ll);
		head(ll)->link.prev = 0p;
	}
}

void ready_queue_grow  (struct cluster * cltr) {
	uint_fast32_t last_size = ready_mutate_lock( *cltr );
	check( cltr->ready_queue );

	with( cltr->ready_queue ) {
		size_t ncount = list.count;

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

		ncount += 4;

		// Allocate new array
		list.data = alloc(list.data, ncount);

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

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

		// Update original
		list.count = ncount;
		// fields in empty don't need to change
	}

	// Make sure that everything is consistent
	check( cltr->ready_queue );
	ready_mutate_unlock( *cltr, last_size );
}

void ready_queue_shrink(struct cluster * cltr) {
	uint_fast32_t last_size = ready_mutate_lock( *cltr );
	with( cltr->ready_queue ) {
		size_t ocount = list.count;
		// Check that we have some space left
		if(ocount < 8) abort("Program attempted to destroy more Ready Queues than were created");

		list.count -= 4;

		// redistribute old data
		verify(ocount > list.count);
		for( idx; (size_t)list.count ~ ocount) {
			// This is not strictly needed but makes checking invariants much easier
			bool locked = __atomic_try_acquire(&list.data[idx].lock);
			verify(locked);
			while(0 != ts(list.data[idx])) {
				struct thread_desc * thrd;
				__attribute__((unused)) bool _;
				[thrd, _] = pop(list.data[idx]);
				verify(thrd);
				push(cltr, thrd);
			}

			__atomic_unlock(&list.data[idx].lock);

			// TODO print the queue statistics here

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

		// clear the now unused masks
		{
			__cfa_readyQ_mask_t fword, fbit, lword, lbit;
			[fbit, fword] = extract(ocount);
			[lbit, lword] = extract(list.count);

			// For now assume that all queues where coverd by the same bitmask
			// This is highly probable as long as grow and shrink use groups of 4
			// exclusively
			verify(fword == lword);
			__cfa_readyQ_mask_t clears = ~0;

			for( b ; fbit ~ lbit ) {
				clears ^= 1 << b;
			}

			empty.mask[fword] &= clears;
		}

		// Allocate new array
		list.data = alloc(list.data, list.count);

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

	// Make sure that everything is consistent
	check( cltr->ready_queue );
	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.full.value, tls.full.value, __ATOMIC_SEQ_CST );
	__atomic_fetch_add( &global_stats.full.count, tls.full.count, __ATOMIC_SEQ_CST );
}
#endif