/*-
 * Copyright (c) 2015 The FreeBSD Foundation
 *
 * This software was developed by Konstantin Belousov
 * under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/queue.h>
#include "namespace.h"
#include <stdlib.h>
#include "un-namespace.h"

#include "thr_private.h"

struct psh {
        LIST_ENTRY(psh) link;
        void *key;
        void *val;
};

LIST_HEAD(pshared_hash_head, psh);
#define HASH_SIZE       128
static struct pshared_hash_head pshared_hash[HASH_SIZE];
#define PSHARED_KEY_HASH(key)   (((unsigned long)(key) >> 8) % HASH_SIZE)
/* XXXKIB: lock could be split to per-hash chain, if appears contested */
static struct urwlock pshared_lock = DEFAULT_URWLOCK;
static int page_size;

void
__thr_pshared_init(void)
{
        int i;

        page_size = getpagesize();
        THR_ASSERT(page_size >= THR_PAGE_SIZE_MIN,
            "THR_PAGE_SIZE_MIN is too large");

        _thr_urwlock_init(&pshared_lock);
        for (i = 0; i < HASH_SIZE; i++)
                LIST_INIT(&pshared_hash[i]);
}

static void
pshared_rlock(struct pthread *curthread)
{

        curthread->locklevel++;
        _thr_rwl_rdlock(&pshared_lock);
}

static void
pshared_wlock(struct pthread *curthread)
{

        curthread->locklevel++;
        _thr_rwl_wrlock(&pshared_lock);
}

static void
pshared_unlock(struct pthread *curthread)
{

        _thr_rwl_unlock(&pshared_lock);
        curthread->locklevel--;
        _thr_ast(curthread);
}

/*
 * Among all processes sharing a lock only one executes
 * pthread_lock_destroy().  Other processes still have the hash and
 * mapped off-page.
 *
 * Mitigate the problem by checking the liveness of all hashed keys
 * periodically.  Right now this is executed on each
 * pthread_lock_destroy(), but may be done less often if found to be
 * too time-consuming.
 */
static void
pshared_gc(struct pthread *curthread)
{
        struct pshared_hash_head *hd;
        struct psh *h, *h1;
        int error, i;

        pshared_wlock(curthread);
        for (i = 0; i < HASH_SIZE; i++) {
                hd = &pshared_hash[i];
                LIST_FOREACH_SAFE(h, hd, link, h1) {
                        error = _umtx_op(NULL, UMTX_OP_SHM, UMTX_SHM_ALIVE,
                            h->val, NULL);
                        if (error == 0)
                                continue;
                        LIST_REMOVE(h, link);
                        munmap(h->val, page_size);
                        free(h);
                }
        }
        pshared_unlock(curthread);
}

static void *
pshared_lookup(void *key)
{
        struct pshared_hash_head *hd;
        struct psh *h;

        hd = &pshared_hash[PSHARED_KEY_HASH(key)];
        LIST_FOREACH(h, hd, link) {
                if (h->key == key)
                        return (h->val);
        }
        return (NULL);
}

static int
pshared_insert(void *key, void **val)
{
        struct pshared_hash_head *hd;
        struct psh *h;

        hd = &pshared_hash[PSHARED_KEY_HASH(key)];
        LIST_FOREACH(h, hd, link) {
                /*
                 * When the key already exists in the hash, we should
                 * return either the new (just mapped) or old (hashed)
                 * val, and the other val should be unmapped to avoid
                 * address space leak.
                 *
                 * If two threads perform lock of the same object
                 * which is not yet stored in the pshared_hash, then
                 * the val already inserted by the first thread should
                 * be returned, and the second val freed (order is by
                 * the pshared_lock()).  Otherwise, if we unmap the
                 * value obtained from the hash, the first thread
                 * might operate on an unmapped off-page object.
                 *
                 * There is still an issue: if hashed key was unmapped
                 * and then other page is mapped at the same key
                 * address, the hash would return the old val.  I
                 * decided to handle the race of simultaneous hash
                 * insertion, leaving the unlikely remap problem
                 * unaddressed.
                 */
                if (h->key == key) {
                        if (h->val != *val) {
                                munmap(*val, page_size);
                                *val = h->val;
                        }
                        return (1);
                }
        }

        h = malloc(sizeof(*h));
        if (h == NULL)
                return (0);
        h->key = key;
        h->val = *val;
        LIST_INSERT_HEAD(hd, h, link);
        return (1);
}

static void *
pshared_remove(void *key)
{
        struct pshared_hash_head *hd;
        struct psh *h;
        void *val;

        hd = &pshared_hash[PSHARED_KEY_HASH(key)];
        LIST_FOREACH(h, hd, link) {
                if (h->key == key) {
                        LIST_REMOVE(h, link);
                        val = h->val;
                        free(h);
                        return (val);
                }
        }
        return (NULL);
}

static void
pshared_clean(void *key, void *val)
{

        if (val != NULL)
                munmap(val, page_size);
        _umtx_op(NULL, UMTX_OP_SHM, UMTX_SHM_DESTROY, key, NULL);
}

static void
pshared_destroy(struct pthread *curthread, void *key)
{
        void *val;

        pshared_wlock(curthread);
        val = pshared_remove(key);
        pshared_unlock(curthread);
        pshared_clean(key, val);
}

void *
__thr_pshared_offpage(void *key, int doalloc)
{
        struct pthread *curthread;
        void *res;
        int fd, ins_done;

        curthread = _get_curthread();
        if (doalloc) {
                pshared_destroy(curthread, key);
                res = NULL;
        } else {
                pshared_rlock(curthread);
                res = pshared_lookup(key);
                pshared_unlock(curthread);
                if (res != NULL)
                        return (res);
        }
        fd = _umtx_op(NULL, UMTX_OP_SHM, doalloc ? UMTX_SHM_CREAT :
            UMTX_SHM_LOOKUP, key, NULL);
        if (fd == -1)
                return (NULL);
        res = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
        close(fd);
        if (res == MAP_FAILED)
                return (NULL);
        pshared_wlock(curthread);
        ins_done = pshared_insert(key, &res);
        pshared_unlock(curthread);
        if (!ins_done) {
                pshared_clean(key, res);
                res = NULL;
        }
        return (res);
}

void
__thr_pshared_destroy(void *key)
{
        struct pthread *curthread;

        curthread = _get_curthread();
        pshared_destroy(curthread, key);
        pshared_gc(curthread);
}

void
__thr_pshared_atfork_pre(void)
{

        _thr_rwl_rdlock(&pshared_lock);
}

void
__thr_pshared_atfork_post(void)
{

        _thr_rwl_unlock(&pshared_lock);
}