impotent/table.h

#pragma once

#include<stdbool.h>
#include<stdint.h>
#include<stddef.h>
#include<ctype.h>
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<stdatomic.h>
#include<assert.h>

#include"value.h"
#include"lrwl.h"

typedef struct LTableEntry {
	LValue key;
	LValue val;
} LTableEntry;

typedef struct LTableBuckets {
	size_t capacity;
	LTableEntry data[];
} LTableBuckets;

typedef struct LTable {
	bool ref;
	LRWL lock;
	size_t border_hint;
	LTableBuckets *buckets;
} LTable;

static inline LTable *ltable_new(size_t capacity) {
	assert(capacity >= 8 && (capacity & (capacity - 1)) == 0);
	
	LTable *tbl = calloc(1, sizeof(*tbl));
	tbl->ref = false;
	tbl->buckets = calloc(1, sizeof(LTableBuckets) + sizeof(LTableEntry) * capacity);
	tbl->buckets->capacity = capacity;
	
	for(size_t i = 0; i < tbl->buckets->capacity; i++) {
		tbl->buckets->data[i] = (LTableEntry) {
			.key = {.u = LTAG_NIL},
			.val = {.u = LTAG_NIL},
		};
	}
	
	return tbl;
}


static bool ltablebuckets_set(LTableBuckets*, LValue, LValue);
// ltable_expand MUST BE CALLED DURING A WRITE LOCK
static void ltable_expand(LTable *self) {
	LTableBuckets *newb = calloc(1, sizeof(*newb) + sizeof(LTableEntry) * (self->buckets->capacity * 2));
	newb->capacity = self->buckets->capacity * 2;
	
	for(size_t i = 0; i < newb->capacity; i++) {
		newb->data[i] = (LTableEntry) {
			.key = {.u = LTAG_NIL},
			.val = {.u = LTAG_NIL},
		};
	}
	
	for(size_t i = 0; i < self->buckets->capacity; i++) {
		LTableEntry *e = &self->buckets->data[i];
		
		if(e->val.u == LTAG_NIL) {
			// Non-existent or tombstone.
		} else {
			assert(e->key.u != LTAG_NIL);
			if(!ltablebuckets_set(newb, e->key, e->val)) {
				// Must expand again.
				free(newb);
				ltable_expand(self);
				return;
			}
		}
	}
	
	LTableBuckets *oldb = self->buckets;
	self->buckets = newb;
	
	free(oldb);
}

static inline bool ltablebuckets_set(LTableBuckets *self, LValue key, LValue val) {
	size_t idx = lvalue_hash(key);

	int probe_limit = __builtin_ctz(self->capacity);
	probe_limit += probe_limit >> 1;

	LTableEntry *current = self->data;
	
	while(1) {
		idx &= self->capacity - 1;
		
		LValue prevKey = {.u = LTAG_NIL};
		atomic_compare_exchange_strong(&current[idx].key.u, &prevKey.u, key.u);
		
		if(prevKey.u == LTAG_NIL || lvalue_eq(prevKey, key)) {
			atomic_store(&current[idx].val.u, val.u);
			break;
		}
		
		idx++;

		probe_limit--;
		if(probe_limit == 0) {
			return false;
		}
	}

	return true;
}

#define L_MAX_SEQUENCE 0x7FFFFFFF
static inline void ltable_set(LTable *self, LValue key, LValue val) {
	if(lvalue_tag(key) == LTAG_FLOAT && nearbyint(key.f) == key.f && fabs(key.f) <= L_MAX_SEQUENCE) {
		intmax_t idx = nearbyint(key.f);
		key = lvalue_from_int32(idx);
	}
	
	// Yes, read lock. Setting itself is lock-free, but other operations may block us.
	lrwl_read_lock(&self->lock);
	bool success = ltablebuckets_set(self->buckets, key, val);
	lrwl_read_unlock(&self->lock);
	
	// Intuitively, it would seem like you should upgrade the RW-lock from read
	// mode to write mode if you need to resize, but I'm pretty sure that's
	// unnecessary? If we fail above, then nothing changes in the table.
	// To the outside, it would look as though this thread happened to set the value a bit later.
	// TODO: Am I correct?
	if(!success) {
		lrwl_write_lock(&self->lock);
		ltable_expand(self);
		ltablebuckets_set(self->buckets, key, val);
		lrwl_write_unlock(&self->lock);
	}
}
static inline void ltable_set_nolock(LTable *self, LValue key, LValue val) {
	if(lvalue_tag(key) == LTAG_FLOAT && nearbyint(key.f) == key.f && fabs(key.f) <= L_MAX_SEQUENCE) {
		intmax_t idx = nearbyint(key.f);
		key = lvalue_from_int32(idx);
	}
	
	if(!ltablebuckets_set(self->buckets, key, val)) {
		ltable_expand(self);
		assert(ltablebuckets_set(self->buckets, key, val));
	}
}

/*static inline bool ltable_set_no_overwrite(LTable *tbl, LValue key, LValue val) {
	LTableBuckets *self = tbl->buckets;
	
	size_t idx = lvalue_hash(key);
	LTableEntry *current = self->data;
	while(1) {
		idx &= self->capacity - 1;
		
		LValue prevKey = {.u = LTAG_NIL};
		atomic_compare_exchange_strong(&current[idx].key.u, &prevKey.u, key.u);
		
		if(prevKey.u == LTAG_NIL) {
			atomic_store(&current[idx].val.u, val.u);
			return true;
		} else if(lvalue_eq(prevKey, key)) {
			return false;
		}
		
		idx++;
	}
}*/

static inline LValue ltablebuckets_get(LTableBuckets *self, LValue key) {
	size_t idx = lvalue_hash(key);
	
	size_t tries = self->capacity;
	
	while(1) {
		idx &= self->capacity - 1;
		
		LValue foundKey;
		foundKey.u = atomic_load(&self->data[idx].key.u);
		
		if(lvalue_eq(foundKey, key)) {
			return (LValue) {.u = atomic_load(&self->data[idx].val.u)};
		} else if(--tries == 0) {
			return (LValue) {.u = LTAG_NIL};
		}
		
		idx++;
	}
}

static inline LValue ltable_get(LTable *self, LValue key) {
	if(lvalue_tag(key) == LTAG_FLOAT && nearbyint(key.f) == key.f && fabs(key.f) <= L_MAX_SEQUENCE) {
		intmax_t idx = nearbyint(key.f);
		key = lvalue_from_int32(idx);
	}
	
	lrwl_read_lock(&self->lock);
	LValue ret = ltablebuckets_get(self->buckets, key);
	lrwl_read_unlock(&self->lock);
	
	return ret;
}
static inline LValue ltable_get_nolock(LTable *self, LValue key) {
	if(lvalue_tag(key) == LTAG_FLOAT && nearbyint(key.f) == key.f && fabs(key.f) <= L_MAX_SEQUENCE) {
		intmax_t idx = nearbyint(key.f);
		key = lvalue_from_int32(idx);
	}
	
	LValue ret = ltablebuckets_get(self->buckets, key);
	
	return ret;
}

static inline size_t ltable_len_nolock(LTable *self) {
	size_t border = self->border_hint;
	if(border == 0 || ltable_get_nolock(self, lvalue_from_int32(border)).u != LTAG_NIL) {
		do {
			border++;
		} while(ltable_get_nolock(self, lvalue_from_int32(border)).u != LTAG_NIL);
		border--;
	} else if(ltable_get_nolock(self, lvalue_from_int32(border)).u == LTAG_NIL) {
		do {
			border--;
		} while(ltable_get_nolock(self, lvalue_from_int32(border)).u == LTAG_NIL);
	}
	self->border_hint = border;
	return border;
}

static inline size_t ltable_len(LTable *self) {
	// As it turns out, finding the length cannot be atomic, and especially cannot be lock-free.
	// Therefore we do a WRITE lock
	lrwl_write_lock(&self->lock);
	size_t ret = ltable_len_nolock(self);
	lrwl_write_unlock(&self->lock);
	return ret;
}

static inline void ltable_insert(LTable *self, LValue val, size_t index) {
	lrwl_write_lock(&self->lock);
	index = ltable_len_nolock(self) + 1;
	ltable_set_nolock(self, lvalue_from_int32(index), val);
	lrwl_write_unlock(&self->lock);
}