sal/rtl/alloc_arena.cxx

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
 * This file is part of the Collabora Office project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This file incorporates work covered by the following license notice:
 *
 *   Licensed to the Apache Software Foundation (ASF) under one or more
 *   contributor license agreements. See the NOTICE file distributed
 *   with this work for additional information regarding copyright
 *   ownership. The ASF licenses this file to you under the Apache
 *   License, Version 2.0 (the "License"); you may not use this file
 *   except in compliance with the License. You may obtain a copy of
 *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
 */

#include <sal/config.h>

#include "alloc_arena.hxx"

#include "alloc_impl.hxx"
#include <rtllifecycle.h>

#include <cassert>
#include <string.h>
#include <stdio.h>

#if defined(SAL_UNX)
#include <unistd.h>
#endif /* SAL_UNX */

namespace {

/**
    @internal
*/
struct rtl_arena_list_st
{
    rtl_memory_lock_type m_lock;
    rtl_arena_type       m_arena_head;
};

}

static rtl_arena_list_st g_arena_list;

/**
    provided for arena_type allocations, and hash_table resizing.

    @internal
*/
static rtl_arena_type * gp_arena_arena = nullptr;

/**
    Low level virtual memory (pseudo) arena
    (platform dependent implementation)

    @internal
 */
static rtl_arena_type * gp_machdep_arena = nullptr;

rtl_arena_type * gp_default_arena = nullptr;

namespace
{

void * rtl_machdep_alloc(
    rtl_arena_type * pArena,
    sal_Size *       pSize
);

void rtl_machdep_free(
    rtl_arena_type * pArena,
    void *           pAddr,
    sal_Size         nSize
);

sal_Size rtl_machdep_pagesize();

void rtl_arena_segment_constructor(void * obj)
{
    rtl_arena_segment_type * segment = static_cast<rtl_arena_segment_type*>(obj);

    QUEUE_START_NAMED(segment, s);
    QUEUE_START_NAMED(segment, f);
}

void rtl_arena_segment_destructor(void * obj)
{
    rtl_arena_segment_type * segment = static_cast< rtl_arena_segment_type * >(
        obj);
    assert(QUEUE_STARTED_NAMED(segment, s));
    assert(QUEUE_STARTED_NAMED(segment, f));
    (void) segment; // avoid warnings
}

/**
    @precond  arena->m_lock acquired.
 */
bool rtl_arena_segment_populate(rtl_arena_type * arena)
{
    rtl_arena_segment_type *span;
    sal_Size                size = rtl_machdep_pagesize();

    span = static_cast< rtl_arena_segment_type * >(
        rtl_machdep_alloc(gp_machdep_arena, &size));
    if (span)
    {
        rtl_arena_segment_type *first, *last, *head;
        sal_Size                count = size / sizeof(rtl_arena_segment_type);

        /* insert onto reserve span list */
        QUEUE_INSERT_TAIL_NAMED(&(arena->m_segment_reserve_span_head), span, s);
        QUEUE_START_NAMED(span, f);
        span->m_addr = reinterpret_cast<sal_uIntPtr>(span);
        span->m_size = size;
        span->m_type = RTL_ARENA_SEGMENT_TYPE_SPAN;

        /* insert onto reserve list */
        head  = &(arena->m_segment_reserve_head);
        for (first = span + 1, last = span + count; first < last; ++first)
        {
            QUEUE_INSERT_TAIL_NAMED(head, first, s);
            QUEUE_START_NAMED(first, f);
            first->m_addr = 0;
            first->m_size = 0;
            first->m_type = 0;
        }
    }
    return (span != nullptr);
}

/**
    @precond  arena->m_lock acquired.
    @precond  (*ppSegment == 0)
*/
void rtl_arena_segment_get(
    rtl_arena_type * arena,
    rtl_arena_segment_type ** ppSegment
)
{
    rtl_arena_segment_type * head;

    assert(!*ppSegment);

    head = &(arena->m_segment_reserve_head);
    if (head->m_snext != head || rtl_arena_segment_populate (arena))
    {
        (*ppSegment) = head->m_snext;
        QUEUE_REMOVE_NAMED(*ppSegment, s);
    }
}

/**
    @precond  arena->m_lock acquired.
    @postcond (*ppSegment == 0)
 */
void rtl_arena_segment_put(
    rtl_arena_type * arena,
    rtl_arena_segment_type ** ppSegment
)
{
    rtl_arena_segment_type * head;

    assert(QUEUE_STARTED_NAMED(*ppSegment, s));
    assert(QUEUE_STARTED_NAMED(*ppSegment, f));

    (*ppSegment)->m_addr = 0;
    (*ppSegment)->m_size = 0;

    assert((*ppSegment)->m_type != RTL_ARENA_SEGMENT_TYPE_HEAD);
    (*ppSegment)->m_type = 0;

    /* keep as reserve */
    head = &(arena->m_segment_reserve_head);
    QUEUE_INSERT_HEAD_NAMED(head, (*ppSegment), s);

    /* clear */
    (*ppSegment) = nullptr;
}

/**
    @precond arena->m_lock acquired.
*/
void rtl_arena_freelist_insert (
    rtl_arena_type * arena,
    rtl_arena_segment_type * segment
)
{
    rtl_arena_segment_type * head;
    const auto bit = highbit(segment->m_size);
    assert(bit > 0);
    head = &(arena->m_freelist_head[bit - 1]);
    QUEUE_INSERT_TAIL_NAMED(head, segment, f);

    arena->m_freelist_bitmap |= head->m_size;
}

/**
    @precond arena->m_lock acquired.
*/
void rtl_arena_freelist_remove(
    rtl_arena_type * arena,
    rtl_arena_segment_type * segment
)
{
    if (segment->m_fnext->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD &&
        segment->m_fprev->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD)
    {
        rtl_arena_segment_type * head;

        head = segment->m_fprev;
        assert(arena->m_freelist_bitmap & head->m_size);
        arena->m_freelist_bitmap ^= head->m_size;
    }
    QUEUE_REMOVE_NAMED(segment, f);
}

#define RTL_ARENA_HASH_INDEX_IMPL(a, s, q, m) \
     ((((a) + ((a) >> (s)) + ((a) >> ((s) << 1))) >> (q)) & (m))

#define RTL_ARENA_HASH_INDEX(arena, addr) \
    RTL_ARENA_HASH_INDEX_IMPL((addr), (arena)->m_hash_shift, (arena)->m_quantum_shift, ((arena)->m_hash_size - 1))

/**
   @precond arena->m_lock released.
*/
void rtl_arena_hash_rescale(
    rtl_arena_type * arena,
    sal_Size new_size
)
{
    assert(new_size != 0);

    rtl_arena_segment_type ** new_table;
    sal_Size                  new_bytes;

    new_bytes = new_size * sizeof(rtl_arena_segment_type*);
    new_table = static_cast<rtl_arena_segment_type **>(rtl_arena_alloc (gp_arena_arena, &new_bytes));

    if (new_table)
    {
        rtl_arena_segment_type ** old_table;
        sal_Size                  old_size, i;

        memset (new_table, 0, new_bytes);

        RTL_MEMORY_LOCK_ACQUIRE(&(arena->m_lock));

        old_table = arena->m_hash_table;
        old_size  = arena->m_hash_size;

        arena->m_hash_table = new_table;
        arena->m_hash_size  = new_size;
        arena->m_hash_shift = highbit(arena->m_hash_size) - 1;

        for (i = 0; i < old_size; i++)
        {
            rtl_arena_segment_type * curr = old_table[i];
            while (curr)
            {
                rtl_arena_segment_type  * next = curr->m_fnext;
                rtl_arena_segment_type ** head;

                head = &(arena->m_hash_table[RTL_ARENA_HASH_INDEX(arena, curr->m_addr)]);
                curr->m_fnext = (*head);
                (*head) = curr;

                curr = next;
            }
            old_table[i] = nullptr;
        }

        RTL_MEMORY_LOCK_RELEASE(&(arena->m_lock));

        if (old_table != arena->m_hash_table_0)
        {
            sal_Size old_bytes = old_size * sizeof(rtl_arena_segment_type*);
            rtl_arena_free (gp_arena_arena, old_table, old_bytes);
        }
    }
}

/**
    Insert arena hash, and update stats.
*/
void rtl_arena_hash_insert(
    rtl_arena_type * arena,
    rtl_arena_segment_type * segment
)
{
    rtl_arena_segment_type ** ppSegment;

    ppSegment = &(arena->m_hash_table[RTL_ARENA_HASH_INDEX(arena, segment->m_addr)]);

    segment->m_fnext = (*ppSegment);
    (*ppSegment) = segment;

    arena->m_stats.m_alloc     += 1;
    arena->m_stats.m_mem_alloc += segment->m_size;
}

/**
    Remove arena hash, and update stats.
*/
rtl_arena_segment_type * rtl_arena_hash_remove(
    rtl_arena_type * arena,
    sal_uIntPtr addr,
    sal_Size size
)
{
    rtl_arena_segment_type *segment, **segpp;
    sal_Size lookups = 0;

    segpp = &(arena->m_hash_table[RTL_ARENA_HASH_INDEX(arena, addr)]);
    while ((segment = *segpp))
    {
        if (segment->m_addr == addr)
        {
            *segpp = segment->m_fnext;
            segment->m_fnext = segment->m_fprev = segment;
            break;
        }

        /* update lookup miss stats */
        lookups += 1;
        segpp = &(segment->m_fnext);
    }

    assert(segment); // bad free
    if (segment)
    {
        assert(segment->m_size == size);
        (void) size; // avoid warnings

        arena->m_stats.m_free      += 1;
        arena->m_stats.m_mem_alloc -= segment->m_size;

        if (lookups > 1)
        {
            sal_Size nseg = static_cast<sal_Size>(arena->m_stats.m_alloc - arena->m_stats.m_free);
            if (nseg > 4 * arena->m_hash_size)
            {
                if (!(arena->m_flags & RTL_ARENA_FLAG_RESCALE))
                {
                    sal_Size ave = nseg >> arena->m_hash_shift;
                    assert(ave != 0);
                    sal_Size new_size = arena->m_hash_size << (highbit(ave) - 1);

                    arena->m_flags |= RTL_ARENA_FLAG_RESCALE;
                    RTL_MEMORY_LOCK_RELEASE(&(arena->m_lock));
                    rtl_arena_hash_rescale (arena, new_size);
                    RTL_MEMORY_LOCK_ACQUIRE(&(arena->m_lock));
                    arena->m_flags &= ~RTL_ARENA_FLAG_RESCALE;
                }
            }
        }
    }

    return segment;
}

/**
    allocate (and remove) segment from freelist

    @precond arena->m_lock acquired
    @precond (*ppSegment == 0)
*/
bool rtl_arena_segment_alloc(
    rtl_arena_type * arena,
    sal_Size size,
    rtl_arena_segment_type ** ppSegment
)
{
    int index = 0;

    assert(!*ppSegment);
    if (!RTL_MEMORY_ISP2(size))
    {
        unsigned int msb = highbit(size);
        if (RTL_ARENA_FREELIST_SIZE == msb)
        {
            /* highest possible freelist: fall back to first fit */
            rtl_arena_segment_type *head, *segment;

            head = &(arena->m_freelist_head[msb - 1]);
            for (segment = head->m_fnext; segment != head; segment = segment->m_fnext)
            {
                if (segment->m_size >= size)
                {
                    /* allocate first fit segment */
                    (*ppSegment) = segment;
                    break;
                }
            }
            goto dequeue_and_leave;
        }

        /* roundup to next power of 2 */
        size = ((sal_Size(1)) << msb);
    }

    index = lowbit(RTL_MEMORY_P2ALIGN(arena->m_freelist_bitmap, size));
    if (index > 0)
    {
        /* instant fit: allocate first free segment */
        rtl_arena_segment_type *head;

        head = &(arena->m_freelist_head[index - 1]);
        (*ppSegment) = head->m_fnext;
        assert((*ppSegment) != head);
    }

dequeue_and_leave:
    if (*ppSegment)
    {
        /* remove from freelist */
        rtl_arena_freelist_remove (arena, (*ppSegment));
    }
    return (*ppSegment != nullptr);
}

/**
    import new (span) segment from source arena

    @precond arena->m_lock acquired
    @precond (*ppSegment == 0)
*/
bool rtl_arena_segment_create(
    rtl_arena_type * arena,
    sal_Size size,
    rtl_arena_segment_type ** ppSegment
)
{
    assert(!*ppSegment);
    if (arena->m_source_alloc)
    {
        rtl_arena_segment_get (arena, ppSegment);
        if (*ppSegment)
        {
            rtl_arena_segment_type * span = nullptr;
            rtl_arena_segment_get (arena, &span);
            if (span)
            {
                /* import new span from source arena */
                RTL_MEMORY_LOCK_RELEASE(&(arena->m_lock));

                span->m_size = size;
                span->m_addr = reinterpret_cast<sal_uIntPtr>(
                    (arena->m_source_alloc)(
                        arena->m_source_arena, &(span->m_size)));

                RTL_MEMORY_LOCK_ACQUIRE(&(arena->m_lock));
                if (span->m_addr != 0)
                {
                    /* insert onto segment list, update stats */
                    span->m_type = RTL_ARENA_SEGMENT_TYPE_SPAN;
                    QUEUE_INSERT_HEAD_NAMED(&(arena->m_segment_head), span, s);
                    arena->m_stats.m_mem_total += span->m_size;

                    (*ppSegment)->m_addr = span->m_addr;
                    (*ppSegment)->m_size = span->m_size;
                    (*ppSegment)->m_type = RTL_ARENA_SEGMENT_TYPE_FREE;
                    QUEUE_INSERT_HEAD_NAMED(span, (*ppSegment), s);

                    /* report success */
                    return true;
                }
                rtl_arena_segment_put (arena, &span);
            }
            rtl_arena_segment_put (arena, ppSegment);
        }
    }
    return false; // failure
}

/**
    mark as free and join with adjacent free segment(s)

    @precond arena->m_lock acquired
    @precond segment marked 'used'
*/
void rtl_arena_segment_coalesce(
    rtl_arena_type * arena,
    rtl_arena_segment_type * segment
)
{
    rtl_arena_segment_type *next, *prev;

    /* mark segment free */
    assert(segment->m_type == RTL_ARENA_SEGMENT_TYPE_USED);
    segment->m_type = RTL_ARENA_SEGMENT_TYPE_FREE;

    /* try to merge w/ next segment */
    next = segment->m_snext;
    if (next->m_type == RTL_ARENA_SEGMENT_TYPE_FREE)
    {
        assert(segment->m_addr + segment->m_size == next->m_addr);
        segment->m_size += next->m_size;

        /* remove from freelist */
        rtl_arena_freelist_remove (arena, next);

        /* remove from segment list */
        QUEUE_REMOVE_NAMED(next, s);

        /* release segment descriptor */
        rtl_arena_segment_put (arena, &next);
    }

    /* try to merge w/ prev segment */
    prev = segment->m_sprev;
    if (prev->m_type == RTL_ARENA_SEGMENT_TYPE_FREE)
    {
        assert(prev->m_addr + prev->m_size == segment->m_addr);
        segment->m_addr  = prev->m_addr;
        segment->m_size += prev->m_size;

        /* remove from freelist */
        rtl_arena_freelist_remove (arena, prev);

        /* remove from segment list */
        QUEUE_REMOVE_NAMED(prev, s);

        /* release segment descriptor */
        rtl_arena_segment_put (arena, &prev);
    }
}

void rtl_arena_constructor(void * obj)
{
    rtl_arena_type * arena = static_cast<rtl_arena_type*>(obj);
    rtl_arena_segment_type * head;
    size_t i;

    memset (arena, 0, sizeof(rtl_arena_type));

    QUEUE_START_NAMED(arena, arena_);

    RTL_MEMORY_LOCK_INIT(&(arena->m_lock));

    head = &(arena->m_segment_reserve_span_head);
    rtl_arena_segment_constructor (head);
    head->m_type = RTL_ARENA_SEGMENT_TYPE_HEAD;

    head = &(arena->m_segment_reserve_head);
    rtl_arena_segment_constructor (head);
    head->m_type = RTL_ARENA_SEGMENT_TYPE_HEAD;

    head = &(arena->m_segment_head);
    rtl_arena_segment_constructor (head);
    head->m_type = RTL_ARENA_SEGMENT_TYPE_HEAD;

    for (i = 0; i < RTL_ARENA_FREELIST_SIZE; i++)
    {
        head = &(arena->m_freelist_head[i]);
        rtl_arena_segment_constructor (head);

        head->m_size = ((sal_Size(1)) << i);
        head->m_type = RTL_ARENA_SEGMENT_TYPE_HEAD;
    }

    arena->m_hash_table = arena->m_hash_table_0;
    arena->m_hash_size  = RTL_ARENA_HASH_SIZE;
    arena->m_hash_shift = highbit(arena->m_hash_size) - 1;
}

void rtl_arena_destructor(void * obj)
{
    rtl_arena_type * arena = static_cast<rtl_arena_type*>(obj);
    rtl_arena_segment_type * head;
    size_t i;

    assert(QUEUE_STARTED_NAMED(arena, arena_));

    RTL_MEMORY_LOCK_DESTROY(&(arena->m_lock));

    head = &(arena->m_segment_reserve_span_head);
    assert(head->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD);
    rtl_arena_segment_destructor (head);

    head = &(arena->m_segment_reserve_head);
    assert(head->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD);
    rtl_arena_segment_destructor (head);

    head = &(arena->m_segment_head);
    assert(head->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD);
    rtl_arena_segment_destructor (head);

    for (i = 0; i < RTL_ARENA_FREELIST_SIZE; i++)
    {
        head = &(arena->m_freelist_head[i]);

        assert(head->m_size == ((sal_Size(1)) << i));
        assert(head->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD);

        rtl_arena_segment_destructor (head);
    }

    assert(arena->m_hash_table == arena->m_hash_table_0);
    assert(arena->m_hash_size  == RTL_ARENA_HASH_SIZE);
    assert(arena->m_hash_shift == highbit(arena->m_hash_size) - 1);
}

rtl_arena_type * rtl_arena_activate(
    rtl_arena_type * arena,
    const char *     name,
    sal_Size         quantum,
    rtl_arena_type * source_arena,
    void * (SAL_CALL * source_alloc)(rtl_arena_type *, sal_Size *),
    void   (SAL_CALL * source_free) (rtl_arena_type *, void *, sal_Size)
)
{
    assert(arena);
    if (arena)
    {
        (void) snprintf (arena->m_name, sizeof(arena->m_name), "%s", name);

        if (!RTL_MEMORY_ISP2(quantum))
        {
            /* roundup to next power of 2 */
            quantum = ((sal_Size(1)) << highbit(quantum));
        }

        arena->m_quantum = quantum;
        arena->m_quantum_shift = highbit(arena->m_quantum) - 1;

        arena->m_source_arena = source_arena;
        arena->m_source_alloc = source_alloc;
        arena->m_source_free  = source_free;

        /* insert into arena list */
        RTL_MEMORY_LOCK_ACQUIRE(&(g_arena_list.m_lock));
        QUEUE_INSERT_TAIL_NAMED(&(g_arena_list.m_arena_head), arena, arena_);
        RTL_MEMORY_LOCK_RELEASE(&(g_arena_list.m_lock));
    }
    return arena;
}

void rtl_arena_deactivate(rtl_arena_type * arena)
{
    rtl_arena_segment_type * head, * segment;

    /* remove from arena list */
    RTL_MEMORY_LOCK_ACQUIRE(&(g_arena_list.m_lock));
    QUEUE_REMOVE_NAMED(arena, arena_);
    RTL_MEMORY_LOCK_RELEASE(&(g_arena_list.m_lock));

    /* check for leaked segments */
    if (arena->m_stats.m_alloc > arena->m_stats.m_free)
    {
        sal_Size i, n;

        /* cleanup still used segment(s) */
        for (i = 0, n = arena->m_hash_size; i < n; i++)
        {
            while ((segment = arena->m_hash_table[i]))
            {
                /* pop from hash table */
                arena->m_hash_table[i] = segment->m_fnext;
                segment->m_fnext = segment->m_fprev = segment;

                /* coalesce w/ adjacent free segment(s) */
                rtl_arena_segment_coalesce (arena, segment);

                /* insert onto freelist */
                rtl_arena_freelist_insert (arena, segment);
            }
        }
    }

    /* cleanup hash table */
    if (arena->m_hash_table != arena->m_hash_table_0)
    {
        rtl_arena_free(
            gp_arena_arena,
            arena->m_hash_table,
            arena->m_hash_size * sizeof(rtl_arena_segment_type*));

        arena->m_hash_table = arena->m_hash_table_0;
        arena->m_hash_size = RTL_ARENA_HASH_SIZE;
        arena->m_hash_shift = highbit(arena->m_hash_size) - 1;
    }

    /* cleanup segment list */
    head = &(arena->m_segment_head);
    for (segment = head->m_snext; segment != head; segment = head->m_snext)
    {
        if (segment->m_type == RTL_ARENA_SEGMENT_TYPE_FREE)
        {
            /* remove from freelist */
            rtl_arena_freelist_remove (arena, segment);
        }
        else
        {
            /* can have only free and span segments here */
            assert(segment->m_type == RTL_ARENA_SEGMENT_TYPE_SPAN);
        }

        /* remove from segment list */
        QUEUE_REMOVE_NAMED(segment, s);

        /* release segment descriptor */
        rtl_arena_segment_put (arena, &segment);
    }

    /* cleanup segment reserve list */
    head = &(arena->m_segment_reserve_head);
    for (segment = head->m_snext; segment != head; segment = head->m_snext)
    {
        /* remove from segment list */
        QUEUE_REMOVE_NAMED(segment, s);
    }

    /* cleanup segment reserve span(s) */
    head = &(arena->m_segment_reserve_span_head);
    for (segment = head->m_snext; segment != head; segment = head->m_snext)
    {
        /* can have only span segments here */
        assert(segment->m_type == RTL_ARENA_SEGMENT_TYPE_SPAN);

        /* remove from segment list */
        QUEUE_REMOVE_NAMED(segment, s);

        /* return span to g_machdep_arena */
        rtl_machdep_free (gp_machdep_arena, reinterpret_cast<void*>(segment->m_addr), segment->m_size);
    }
}

} // namespace

rtl_arena_type * SAL_CALL rtl_arena_create(
    const char *       name,
    sal_Size           quantum,
    sal_Size,
    rtl_arena_type *   source_arena,
    void * (SAL_CALL * source_alloc)(rtl_arena_type *, sal_Size *),
    void   (SAL_CALL * source_free) (rtl_arena_type *, void *, sal_Size),
    SAL_UNUSED_PARAMETER int
) noexcept
{
    rtl_arena_type * result = nullptr;
    sal_Size         size   = sizeof(rtl_arena_type);

try_alloc:
    result = static_cast<rtl_arena_type*>(rtl_arena_alloc (gp_arena_arena, &size));
    if (result)
    {
        rtl_arena_type * arena = result;
        rtl_arena_constructor (arena);

        if (!source_arena)
        {
            assert(gp_default_arena);
            source_arena = gp_default_arena;
        }

        result = rtl_arena_activate (
            arena,
            name,
            quantum,
            source_arena,
            source_alloc,
            source_free
        );

        if (!result)
        {
            rtl_arena_deactivate (arena);
            rtl_arena_destructor (arena);
            rtl_arena_free (gp_arena_arena, arena, size);
        }
    }
    else if (!gp_arena_arena)
    {
        ensureArenaSingleton();
        if (gp_arena_arena)
        {
            /* try again */
            goto try_alloc;
        }
    }
    return result;
}

void SAL_CALL rtl_arena_destroy(rtl_arena_type * arena) noexcept
{
    if (arena)
    {
        rtl_arena_deactivate (arena);
        rtl_arena_destructor (arena);
        rtl_arena_free (gp_arena_arena, arena, sizeof(rtl_arena_type));
    }
}

void * SAL_CALL rtl_arena_alloc(
    rtl_arena_type * arena,
    sal_Size *       pSize
) noexcept
{
    void * addr = nullptr;

    if (arena && pSize)
    {
        sal_Size size;

        size = RTL_MEMORY_ALIGN(*pSize, arena->m_quantum);
        if (size > 0)
        {
            /* allocate from segment list */
            rtl_arena_segment_type *segment = nullptr;

            RTL_MEMORY_LOCK_ACQUIRE(&(arena->m_lock));
            if (rtl_arena_segment_alloc (arena, size, &segment) ||
                rtl_arena_segment_create(arena, size, &segment)    )
            {
                /* shrink to fit */
                sal_Size oversize;

                /* mark segment used */
                assert(segment->m_type == RTL_ARENA_SEGMENT_TYPE_FREE);
                segment->m_type = RTL_ARENA_SEGMENT_TYPE_USED;

                /* resize */
                assert(segment->m_size >= size);
                oversize = segment->m_size - size;
                if (oversize >= arena->m_quantum)
                {
                    rtl_arena_segment_type * remainder = nullptr;
                    rtl_arena_segment_get (arena, &remainder);
                    if (remainder)
                    {
                        segment->m_size = size;

                        remainder->m_addr = segment->m_addr + segment->m_size;
                        remainder->m_size = oversize;
                        remainder->m_type = RTL_ARENA_SEGMENT_TYPE_FREE;
                        QUEUE_INSERT_HEAD_NAMED(segment, remainder, s);

                        rtl_arena_freelist_insert (arena, remainder);
                    }
                }

                rtl_arena_hash_insert (arena, segment);

                (*pSize) = segment->m_size;
                addr = reinterpret_cast<void*>(segment->m_addr);
            }
            RTL_MEMORY_LOCK_RELEASE(&(arena->m_lock));
        }
    }
    return addr;
}

void SAL_CALL rtl_arena_free (
    rtl_arena_type * arena,
    void *           addr,
    sal_Size         size
) noexcept
{
    if (arena)
    {
        size = RTL_MEMORY_ALIGN(size, arena->m_quantum);
        if (size > 0)
        {
            /* free to segment list */
            rtl_arena_segment_type * segment;

            RTL_MEMORY_LOCK_ACQUIRE(&(arena->m_lock));

            segment = rtl_arena_hash_remove (arena, reinterpret_cast<sal_uIntPtr>(addr), size);
            if (segment)
            {
                rtl_arena_segment_type *next, *prev;

                /* coalesce w/ adjacent free segment(s) */
                rtl_arena_segment_coalesce (arena, segment);

                /* determine (new) next and prev segment */
                next = segment->m_snext;
                prev = segment->m_sprev;

                /* entire span free when prev is a span, and next is either a span or a list head */
                if (prev->m_type == RTL_ARENA_SEGMENT_TYPE_SPAN &&
                    ((next->m_type == RTL_ARENA_SEGMENT_TYPE_SPAN)  ||
                     (next->m_type == RTL_ARENA_SEGMENT_TYPE_HEAD)))
                {
                    assert(
                        prev->m_addr == segment->m_addr
                        && prev->m_size == segment->m_size);

                    if (arena->m_source_free)
                    {
                        addr = reinterpret_cast<void*>(prev->m_addr);
                        size = prev->m_size;

                        /* remove from segment list */
                        QUEUE_REMOVE_NAMED(segment, s);

                        /* release segment descriptor */
                        rtl_arena_segment_put (arena, &segment);

                        /* remove from segment list */
                        QUEUE_REMOVE_NAMED(prev, s);

                        /* release (span) segment descriptor */
                        rtl_arena_segment_put (arena, &prev);

                        /* update stats, return span to source arena */
                        arena->m_stats.m_mem_total -= size;
                        RTL_MEMORY_LOCK_RELEASE(&(arena->m_lock));

                        (arena->m_source_free)(arena->m_source_arena, addr, size);
                        return;
                    }
                }

                /* insert onto freelist */
                rtl_arena_freelist_insert (arena, segment);
            }

            RTL_MEMORY_LOCK_RELEASE(&(arena->m_lock));
        }
    }
}

void rtl_arena_foreach (rtl_arena_type *arena, ArenaForeachFn foreachFn)
{
    /* used segments */
    for (int i = 0, n = arena->m_hash_size; i < n; i++)
    {
        for (rtl_arena_segment_type *segment = arena->m_hash_table[i];
             segment != nullptr; segment = segment->m_fnext)
        {
            foreachFn(reinterpret_cast<void *>(segment->m_addr),
                      segment->m_size);
        }
    }
}

#if defined(SAL_UNX)
#include <sys/mman.h>
#elif defined(_WIN32)
#define MAP_FAILED nullptr
#endif /* SAL_UNX || _WIN32 */

namespace
{

void * rtl_machdep_alloc(
    rtl_arena_type * pArena,
    sal_Size *       pSize
)
{
    void *   addr;
    sal_Size size = *pSize;

    assert(pArena == gp_machdep_arena);

#if defined(__sun) && defined(SPARC)
    /* see @ mmap(2) man pages */
    size += (pArena->m_quantum + pArena->m_quantum); /* "red-zone" pages */
    if (size > (4 << 20))
        size = RTL_MEMORY_P2ROUNDUP(size, (4 << 20));
    else if (size > (512 << 10))
        size = RTL_MEMORY_P2ROUNDUP(size, (512 << 10));
    else
        size = RTL_MEMORY_P2ROUNDUP(size, (64 << 10));
    size -= (pArena->m_quantum + pArena->m_quantum); /* "red-zone" pages */
#else
    /* default allocation granularity */
    if (pArena->m_quantum < (64 << 10))
    {
        size = RTL_MEMORY_P2ROUNDUP(size, (64 << 10));
    }
    else
    {
        size = RTL_MEMORY_P2ROUNDUP(size, pArena->m_quantum);
    }
#endif

#if defined(SAL_UNX)
    addr = mmap (nullptr, static_cast<size_t>(size), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
#elif defined(_WIN32)
    addr = VirtualAlloc (nullptr, static_cast<SIZE_T>(size), MEM_COMMIT, PAGE_READWRITE);
#endif /* (SAL_UNX || _WIN32) */

    if (addr != MAP_FAILED)
    {
        pArena->m_stats.m_alloc += 1;
        pArena->m_stats.m_mem_total += size;
        pArena->m_stats.m_mem_alloc += size;

        (*pSize) = size;
        return addr;
    }
    return nullptr;
}

void rtl_machdep_free(
    rtl_arena_type * pArena,
    void *           pAddr,
    sal_Size         nSize
)
{
    assert(pArena == gp_machdep_arena);

    pArena->m_stats.m_free += 1;
    pArena->m_stats.m_mem_total -= nSize;
    pArena->m_stats.m_mem_alloc -= nSize;

#if defined(SAL_UNX)
    (void) munmap(pAddr, nSize);
#elif defined(_WIN32)
    (void) VirtualFree (pAddr, SIZE_T(0), MEM_RELEASE);
#endif /* (SAL_UNX || _WIN32) */
}

sal_Size rtl_machdep_pagesize()
{
#if defined(SAL_UNX)
#if defined(FREEBSD) || defined(NETBSD) || defined(DRAGONFLY)
    return (sal_Size)getpagesize();
#else  /* POSIX */
    return static_cast<sal_Size>(sysconf(_SC_PAGESIZE));
#endif /* xBSD || POSIX */
#elif defined(_WIN32)
    SYSTEM_INFO info;
    GetSystemInfo (&info);
    return static_cast<sal_Size>(info.dwPageSize);
#endif /* (SAL_UNX || _WIN32) */
}

} //namespace

void rtl_arena_init()
{
    {
        /* list of arenas */
        RTL_MEMORY_LOCK_INIT(&(g_arena_list.m_lock));
        rtl_arena_constructor (&(g_arena_list.m_arena_head));
    }
    {
        /* machdep (pseudo) arena */
        static rtl_arena_type g_machdep_arena;

        assert(!gp_machdep_arena);
        rtl_arena_constructor (&g_machdep_arena);

        gp_machdep_arena = rtl_arena_activate (
            &g_machdep_arena,
            "rtl_machdep_arena",
            rtl_machdep_pagesize(),
            nullptr, nullptr, nullptr  /* no source */
        );
        assert(gp_machdep_arena);
    }
    {
        /* default arena */
        static rtl_arena_type g_default_arena;

        assert(!gp_default_arena);
        rtl_arena_constructor (&g_default_arena);

        gp_default_arena = rtl_arena_activate (
            &g_default_arena,
            "rtl_default_arena",
            rtl_machdep_pagesize(),
            gp_machdep_arena,  /* source */
            rtl_machdep_alloc,
            rtl_machdep_free
        );
        assert(gp_default_arena);
    }
    {
        /* arena internal arena */
        static rtl_arena_type g_arena_arena;

        assert(!gp_arena_arena);
        rtl_arena_constructor (&g_arena_arena);

        gp_arena_arena = rtl_arena_activate(
            &g_arena_arena,
            "rtl_arena_internal_arena",
            64,                /* quantum */
            gp_default_arena,  /* source */
            rtl_arena_alloc,
            rtl_arena_free
        );
        assert(gp_arena_arena);
    }
}

void rtl_arena_fini()
{
    if (gp_arena_arena)
    {
        rtl_arena_type * arena, * head;

        RTL_MEMORY_LOCK_ACQUIRE(&(g_arena_list.m_lock));
        head = &(g_arena_list.m_arena_head);

        for (arena = head->m_arena_next; arena != head; arena = arena->m_arena_next)
        {
            // noop
        }
        RTL_MEMORY_LOCK_RELEASE(&(g_arena_list.m_lock));
    }
}

/* vim:set shiftwidth=4 softtabstop=4 expandtab: */