port/gen/malloc.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*  Copyright (c) 1988 AT&T */
/*    All Rights Reserved   */

#pragma ident   "%Z%%M% %I% %E% SMI"

/*
 *  Memory management: malloc(), realloc(), free().
 *
 *  The following #-parameters may be redefined:
 *  SEGMENTED: if defined, memory requests are assumed to be
 *      non-contiguous across calls of GETCORE's.
 *  GETCORE: a function to get more core memory. If not SEGMENTED,
 *      GETCORE(0) is assumed to return the next available
 *      address. Default is 'sbrk'.
 *  ERRCORE: the error code as returned by GETCORE.
 *      Default is (char *)(-1).
 *  CORESIZE: a desired unit (measured in bytes) to be used
 *      with GETCORE. Default is (1024*ALIGN).
 *
 *  This algorithm is based on a  best fit strategy with lists of
 *  free elts maintained in a self-adjusting binary tree. Each list
 *  contains all elts of the same size. The tree is ordered by size.
 *  For results on self-adjusting trees, see the paper:
 *      Self-Adjusting Binary Trees,
 *      DD Sleator & RE Tarjan, JACM 1985.
 *
 *  The header of a block contains the size of the data part in bytes.
 *  Since the size of a block is 0%4, the low two bits of the header
 *  are free and used as follows:
 *
 *      BIT0:   1 for busy (block is in use), 0 for free.
 *      BIT1:   if the block is busy, this bit is 1 if the
 *          preceding block in contiguous memory is free.
 *          Otherwise, it is always 0.
 */

#include "lint.h"
#include "mallint.h"
#include "mtlib.h"

/*
 * Some abusers of the system (notably java1.2) acquire __malloc_lock
 * in order to prevent threads from holding it while they are being
 * suspended via thr_suspend() or thr_suspend_allmutators().
 * This never worked when alternate malloc() libraries were used
 * because they don't use __malloc_lock for their locking strategy.
 * We leave __malloc_lock as an external variable to satisfy these
 * old programs, but we define a new lock, private to libc, to do the
 * real locking: libc_malloc_lock.  This puts libc's malloc() package
 * on the same footing as all other malloc packages.
 */
mutex_t __malloc_lock = DEFAULTMUTEX;
mutex_t libc_malloc_lock = DEFAULTMUTEX;

static TREE *Root,      /* root of the free tree */
        *Bottom,    /* the last free chunk in the arena */
        *_morecore(size_t); /* function to get more core */

static char *Baddr;     /* current high address of the arena */
static char *Lfree;     /* last freed block with data intact */

static void t_delete(TREE *);
static void t_splay(TREE *);
static void realfree(void *);
static void cleanfree(void *);
static void *_malloc_unlocked(size_t);

#define FREESIZE (1<<5) /* size for preserving free blocks until next malloc */
#define FREEMASK FREESIZE-1

static void *flist[FREESIZE];   /* list of blocks to be freed on next malloc */
static int freeidx;     /* index of free blocks in flist % FREESIZE */

/*
 * Interfaces used only by atfork_init() functions.
 */
void
malloc_locks(void)
{
    (void) mutex_lock(&libc_malloc_lock);
}

void
malloc_unlocks(void)
{
    (void) mutex_unlock(&libc_malloc_lock);
}

/*
 *  Allocation of small blocks
 */
static TREE *List[MINSIZE/WORDSIZE-1]; /* lists of small blocks */

static void *
_smalloc(size_t size)
{
    TREE    *tp;
    size_t  i;

    ASSERT(size % WORDSIZE == 0);
    /* want to return a unique pointer on malloc(0) */
    if (size == 0)
        size = WORDSIZE;

    /* list to use */
    i = size / WORDSIZE - 1;

    if (List[i] == NULL) {
        TREE *np;
        int n;
        /* number of blocks to get at one time */
#define NPS (WORDSIZE*8)
        ASSERT((size + WORDSIZE) * NPS >= MINSIZE);

        /* get NPS of these block types */
        if ((List[i] = _malloc_unlocked((size + WORDSIZE) * NPS)) == 0)
            return (0);

        /* make them into a link list */
        for (n = 0, np = List[i]; n < NPS; ++n) {
            tp = np;
            SIZE(tp) = size;
            np = NEXT(tp);
            AFTER(tp) = np;
        }
        AFTER(tp) = NULL;
    }

    /* allocate from the head of the queue */
    tp = List[i];
    List[i] = AFTER(tp);
    SETBIT0(SIZE(tp));
    return (DATA(tp));
}

void *
malloc(size_t size)
{
    void *ret;

    if (!primary_link_map) {
        errno = ENOTSUP;
        return (NULL);
    }
    assert_no_libc_locks_held();
    (void) mutex_lock(&libc_malloc_lock);
    ret = _malloc_unlocked(size);
    (void) mutex_unlock(&libc_malloc_lock);
    return (ret);
}

static void *
_malloc_unlocked(size_t size)
{
    size_t  n;
    TREE    *tp, *sp;
    size_t  o_bit1;

    COUNT(nmalloc);
    ASSERT(WORDSIZE == ALIGN);

    /* check for size that could overflow calculations */
    if (size > MAX_MALLOC) {
        errno = ENOMEM;
        return (NULL);
    }

    /* make sure that size is 0 mod ALIGN */
    ROUND(size);

    /* see if the last free block can be used */
    if (Lfree) {
        sp = BLOCK(Lfree);
        n = SIZE(sp);
        CLRBITS01(n);
        if (n == size) {
            /*
             * exact match, use it as is
             */
            freeidx = (freeidx + FREESIZE - 1) &
                FREEMASK; /* 1 back */
            flist[freeidx] = Lfree = NULL;
            return (DATA(sp));
        } else if (size >= MINSIZE && n > size) {
            /*
             * got a big enough piece
             */
            freeidx = (freeidx + FREESIZE - 1) &
                FREEMASK; /* 1 back */
            flist[freeidx] = Lfree = NULL;
            o_bit1 = SIZE(sp) & BIT1;
            SIZE(sp) = n;
            goto leftover;
        }
    }
    o_bit1 = 0;

    /* perform free's of space since last malloc */
    cleanfree(NULL);

    /* small blocks */
    if (size < MINSIZE)
        return (_smalloc(size));

    /* search for an elt of the right size */
    sp = NULL;
    n  = 0;
    if (Root) {
        tp = Root;
        for (;;) {
            /* branch left */
            if (SIZE(tp) >= size) {
                if (n == 0 || n >= SIZE(tp)) {
                    sp = tp;
                    n = SIZE(tp);
                }
                if (LEFT(tp))
                    tp = LEFT(tp);
                else
                    break;
            } else { /* branch right */
                if (RIGHT(tp))
                    tp = RIGHT(tp);
                else
                    break;
            }
        }

        if (sp) {
            t_delete(sp);
        } else if (tp != Root) {
            /* make the searched-to element the root */
            t_splay(tp);
            Root = tp;
        }
    }

    /* if found none fitted in the tree */
    if (!sp) {
        if (Bottom && size <= SIZE(Bottom)) {
            sp = Bottom;
            CLRBITS01(SIZE(sp));
        } else if ((sp = _morecore(size)) == NULL) /* no more memory */
            return (NULL);
    }

    /* tell the forward neighbor that we're busy */
    CLRBIT1(SIZE(NEXT(sp)));

    ASSERT(ISBIT0(SIZE(NEXT(sp))));

leftover:
    /* if the leftover is enough for a new free piece */
    if ((n = (SIZE(sp) - size)) >= MINSIZE + WORDSIZE) {
        n -= WORDSIZE;
        SIZE(sp) = size;
        tp = NEXT(sp);
        SIZE(tp) = n|BIT0;
        realfree(DATA(tp));
    } else if (BOTTOM(sp))
        Bottom = NULL;

    /* return the allocated space */
    SIZE(sp) |= BIT0 | o_bit1;
    return (DATA(sp));
}


/*
 * realloc().
 *
 * If the block size is increasing, we try forward merging first.
 * This is not best-fit but it avoids some data recopying.
 */
void *
realloc(void *old, size_t size)
{
    TREE    *tp, *np;
    size_t  ts;
    char    *new;

    if (!primary_link_map) {
        errno = ENOTSUP;
        return (NULL);
    }

    assert_no_libc_locks_held();
    COUNT(nrealloc);

    /* check for size that could overflow calculations */
    if (size > MAX_MALLOC) {
        errno = ENOMEM;
        return (NULL);
    }

    /* pointer to the block */
    (void) mutex_lock(&libc_malloc_lock);
    if (old == NULL) {
        new = _malloc_unlocked(size);
        (void) mutex_unlock(&libc_malloc_lock);
        return (new);
    }

    /* perform free's of space since last malloc */
    cleanfree(old);

    /* make sure that size is 0 mod ALIGN */
    ROUND(size);

    tp = BLOCK(old);
    ts = SIZE(tp);

    /* if the block was freed, data has been destroyed. */
    if (!ISBIT0(ts)) {
        (void) mutex_unlock(&libc_malloc_lock);
        return (NULL);
    }

    /* nothing to do */
    CLRBITS01(SIZE(tp));
    if (size == SIZE(tp)) {
        SIZE(tp) = ts;
        (void) mutex_unlock(&libc_malloc_lock);
        return (old);
    }

    /* special cases involving small blocks */
    if (size < MINSIZE || SIZE(tp) < MINSIZE) {
        /* free is size is zero */
        if (size == 0) {
            SETOLD01(SIZE(tp), ts);
            _free_unlocked(old);
            (void) mutex_unlock(&libc_malloc_lock);
            return (NULL);
        } else {
            goto call_malloc;
        }
    }

    /* block is increasing in size, try merging the next block */
    if (size > SIZE(tp)) {
        np = NEXT(tp);
        if (!ISBIT0(SIZE(np))) {
            ASSERT(SIZE(np) >= MINSIZE);
            ASSERT(!ISBIT1(SIZE(np)));
            SIZE(tp) += SIZE(np) + WORDSIZE;
            if (np != Bottom)
                t_delete(np);
            else
                Bottom = NULL;
            CLRBIT1(SIZE(NEXT(np)));
        }

#ifndef SEGMENTED
        /* not enough & at TRUE end of memory, try extending core */
        if (size > SIZE(tp) && BOTTOM(tp) && GETCORE(0) == Baddr) {
            Bottom = tp;
            if ((tp = _morecore(size)) == NULL) {
                tp = Bottom;
                Bottom = NULL;
                }
        }
#endif
    }

    /* got enough space to use */
    if (size <= SIZE(tp)) {
        size_t n;

chop_big:
        if ((n = (SIZE(tp) - size)) >= MINSIZE + WORDSIZE) {
            n -= WORDSIZE;
            SIZE(tp) = size;
            np = NEXT(tp);
            SIZE(np) = n|BIT0;
            realfree(DATA(np));
        } else if (BOTTOM(tp))
            Bottom = NULL;

        /* the previous block may be free */
        SETOLD01(SIZE(tp), ts);
        (void) mutex_unlock(&libc_malloc_lock);
        return (old);
    }

    /* call malloc to get a new block */
call_malloc:
    SETOLD01(SIZE(tp), ts);
    if ((new = _malloc_unlocked(size)) != NULL) {
        CLRBITS01(ts);
        if (ts > size)
            ts = size;
        MEMCOPY(new, old, ts);
        _free_unlocked(old);
        (void) mutex_unlock(&libc_malloc_lock);
        return (new);
    }

    /*
     * Attempt special case recovery allocations since malloc() failed:
     *
     * 1. size <= SIZE(tp) < MINSIZE
     *  Simply return the existing block
     * 2. SIZE(tp) < size < MINSIZE
     *  malloc() may have failed to allocate the chunk of
     *  small blocks. Try asking for MINSIZE bytes.
     * 3. size < MINSIZE <= SIZE(tp)
     *  malloc() may have failed as with 2.  Change to
     *  MINSIZE allocation which is taken from the beginning
     *  of the current block.
     * 4. MINSIZE <= SIZE(tp) < size
     *  If the previous block is free and the combination of
     *  these two blocks has at least size bytes, then merge
     *  the two blocks copying the existing contents backwards.
     */
    CLRBITS01(SIZE(tp));
    if (SIZE(tp) < MINSIZE) {
        if (size < SIZE(tp)) {          /* case 1. */
            SETOLD01(SIZE(tp), ts);
            (void) mutex_unlock(&libc_malloc_lock);
            return (old);
        } else if (size < MINSIZE) {        /* case 2. */
            size = MINSIZE;
            goto call_malloc;
        }
    } else if (size < MINSIZE) {            /* case 3. */
        size = MINSIZE;
        goto chop_big;
    } else if (ISBIT1(ts) &&
        (SIZE(np = LAST(tp)) + SIZE(tp) + WORDSIZE) >= size) {
        ASSERT(!ISBIT0(SIZE(np)));
        t_delete(np);
        SIZE(np) += SIZE(tp) + WORDSIZE;
        /*
         * Since the copy may overlap, use memmove() if available.
         * Otherwise, copy by hand.
         */
        (void) memmove(DATA(np), old, SIZE(tp));
        old = DATA(np);
        tp = np;
        CLRBIT1(ts);
        goto chop_big;
    }
    SETOLD01(SIZE(tp), ts);
    (void) mutex_unlock(&libc_malloc_lock);
    return (NULL);
}


/*
 * realfree().
 *
 * Coalescing of adjacent free blocks is done first.
 * Then, the new free block is leaf-inserted into the free tree
 * without splaying. This strategy does not guarantee the amortized
 * O(nlogn) behaviour for the insert/delete/find set of operations
 * on the tree. In practice, however, free is much more infrequent
 * than malloc/realloc and the tree searches performed by these
 * functions adequately keep the tree in balance.
 */
static void
realfree(void *old)
{
    TREE    *tp, *sp, *np;
    size_t  ts, size;

    COUNT(nfree);

    /* pointer to the block */
    tp = BLOCK(old);
    ts = SIZE(tp);
    if (!ISBIT0(ts))
        return;
    CLRBITS01(SIZE(tp));

    /* small block, put it in the right linked list */
    if (SIZE(tp) < MINSIZE) {
        ASSERT(SIZE(tp) / WORDSIZE >= 1);
        ts = SIZE(tp) / WORDSIZE - 1;
        AFTER(tp) = List[ts];
        List[ts] = tp;
        return;
    }

    /* see if coalescing with next block is warranted */
    np = NEXT(tp);
    if (!ISBIT0(SIZE(np))) {
        if (np != Bottom)
            t_delete(np);
        SIZE(tp) += SIZE(np) + WORDSIZE;
    }

    /* the same with the preceding block */
    if (ISBIT1(ts)) {
        np = LAST(tp);
        ASSERT(!ISBIT0(SIZE(np)));
        ASSERT(np != Bottom);
        t_delete(np);
        SIZE(np) += SIZE(tp) + WORDSIZE;
        tp = np;
    }

    /* initialize tree info */
    PARENT(tp) = LEFT(tp) = RIGHT(tp) = LINKFOR(tp) = NULL;

    /* the last word of the block contains self's address */
    *(SELFP(tp)) = tp;

    /* set bottom block, or insert in the free tree */
    if (BOTTOM(tp))
        Bottom = tp;
    else {
        /* search for the place to insert */
        if (Root) {
            size = SIZE(tp);
            np = Root;
            for (;;) {
                if (SIZE(np) > size) {
                    if (LEFT(np))
                        np = LEFT(np);
                    else {
                        LEFT(np) = tp;
                        PARENT(tp) = np;
                        break;
                    }
                } else if (SIZE(np) < size) {
                    if (RIGHT(np))
                        np = RIGHT(np);
                    else {
                        RIGHT(np) = tp;
                        PARENT(tp) = np;
                        break;
                    }
                } else {
                    if ((sp = PARENT(np)) != NULL) {
                        if (np == LEFT(sp))
                            LEFT(sp) = tp;
                        else
                            RIGHT(sp) = tp;
                        PARENT(tp) = sp;
                    } else
                        Root = tp;

                    /* insert to head of list */
                    if ((sp = LEFT(np)) != NULL)
                        PARENT(sp) = tp;
                    LEFT(tp) = sp;

                    if ((sp = RIGHT(np)) != NULL)
                        PARENT(sp) = tp;
                    RIGHT(tp) = sp;

                    /* doubly link list */
                    LINKFOR(tp) = np;
                    LINKBAK(np) = tp;
                    SETNOTREE(np);

                    break;
                }
            }
        } else
            Root = tp;
    }

    /* tell next block that this one is free */
    SETBIT1(SIZE(NEXT(tp)));

    ASSERT(ISBIT0(SIZE(NEXT(tp))));
}

/*
 * Get more core. Gaps in memory are noted as busy blocks.
 */
static TREE *
_morecore(size_t size)
{
    TREE    *tp;
    ssize_t n, offset;
    char    *addr;
    ssize_t nsize;

    /* compute new amount of memory to get */
    tp = Bottom;
    n = (ssize_t)size + 2 * WORDSIZE;
    addr = GETCORE(0);

    if (addr == ERRCORE)
        return (NULL);

    /* need to pad size out so that addr is aligned */
    if ((((uintptr_t)addr) % ALIGN) != 0)
        offset = ALIGN - (uintptr_t)addr % ALIGN;
    else
        offset = 0;

#ifndef SEGMENTED
    /* if not segmented memory, what we need may be smaller */
    if (addr == Baddr) {
        n -= WORDSIZE;
        if (tp != NULL)
            n -= SIZE(tp);
    }
#endif

    /* get a multiple of CORESIZE */
    n = ((n - 1) / CORESIZE + 1) * CORESIZE;
    nsize = n + offset;

    /* check if nsize request could overflow in GETCORE */
    if ((size_t)nsize > MAX_MALLOC - (uintptr_t)addr) {
        errno = ENOMEM;
        return (NULL);
    }

    if ((size_t)nsize <= MAX_GETCORE) {
        if (GETCORE(nsize) == ERRCORE)
            return (NULL);
    } else {
        intptr_t    delta;
        /*
         * the value required is too big for GETCORE() to deal with
         * in one go, so use GETCORE() at most 2 times instead.
         * Argument to GETCORE() must be multiple of ALIGN.
         * If not, GETCORE(-MAX_GETCORE) will not return brk point
         * to previous value, but will be ALIGN more.
         * This would leave a small hole.
         */
        delta = MAX_GETCORE;
        while (delta > 0) {
            if (GETCORE(delta) == ERRCORE) {
                if (addr != GETCORE(0))
                    (void) GETCORE(-MAX_GETCORE);
                return (NULL);
            }
            nsize -= MAX_GETCORE;
            delta = nsize;
        }
    }

    /* contiguous memory */
    if (addr == Baddr) {
        ASSERT(offset == 0);
        if (tp) {
            addr = (char *)tp;
            n += SIZE(tp) + 2 * WORDSIZE;
        } else {
            addr = Baddr - WORDSIZE;
            n += WORDSIZE;
        }
    } else
        addr += offset;

    /* new bottom address */
    Baddr = addr + n;

    /* new bottom block */
    tp = (TREE *)(uintptr_t)addr;
    SIZE(tp) = n - 2 * WORDSIZE;
    ASSERT((SIZE(tp) % ALIGN) == 0);

    /* reserved the last word to head any noncontiguous memory */
    SETBIT0(SIZE(NEXT(tp)));

    /* non-contiguous memory, free old bottom block */
    if (Bottom && Bottom != tp) {
        SETBIT0(SIZE(Bottom));
        realfree(DATA(Bottom));
    }

    return (tp);
}


/*
 * Tree rotation functions (BU: bottom-up, TD: top-down)
 */

#define LEFT1(x, y)     \
            if ((RIGHT(x) = LEFT(y)) != NULL) PARENT(RIGHT(x)) = x;\
            if ((PARENT(y) = PARENT(x)) != NULL)\
                if (LEFT(PARENT(x)) == x) LEFT(PARENT(y)) = y;\
                else RIGHT(PARENT(y)) = y;\
            LEFT(y) = x; PARENT(x) = y

#define RIGHT1(x, y)        \
            if ((LEFT(x) = RIGHT(y)) != NULL) PARENT(LEFT(x)) = x;\
            if ((PARENT(y) = PARENT(x)) != NULL)\
                if (LEFT(PARENT(x)) == x) LEFT(PARENT(y)) = y;\
                else RIGHT(PARENT(y)) = y;\
            RIGHT(y) = x; PARENT(x) = y

#define BULEFT2(x, y, z)    \
            if ((RIGHT(x) = LEFT(y)) != NULL) PARENT(RIGHT(x)) = x;\
            if ((RIGHT(y) = LEFT(z)) != NULL) PARENT(RIGHT(y)) = y;\
            if ((PARENT(z) = PARENT(x)) != NULL)\
                if (LEFT(PARENT(x)) == x) LEFT(PARENT(z)) = z;\
                else RIGHT(PARENT(z)) = z;\
            LEFT(z) = y; PARENT(y) = z; LEFT(y) = x; PARENT(x) = y

#define BURIGHT2(x, y, z)   \
            if ((LEFT(x) = RIGHT(y)) != NULL) PARENT(LEFT(x)) = x;\
            if ((LEFT(y) = RIGHT(z)) != NULL) PARENT(LEFT(y)) = y;\
            if ((PARENT(z) = PARENT(x)) != NULL)\
                if (LEFT(PARENT(x)) == x) LEFT(PARENT(z)) = z;\
                else RIGHT(PARENT(z)) = z;\
            RIGHT(z) = y; PARENT(y) = z; RIGHT(y) = x; PARENT(x) = y

#define TDLEFT2(x, y, z)    \
            if ((RIGHT(y) = LEFT(z)) != NULL) PARENT(RIGHT(y)) = y;\
            if ((PARENT(z) = PARENT(x)) != NULL)\
                if (LEFT(PARENT(x)) == x) LEFT(PARENT(z)) = z;\
                else RIGHT(PARENT(z)) = z;\
            PARENT(x) = z; LEFT(z) = x;

#define TDRIGHT2(x, y, z)   \
            if ((LEFT(y) = RIGHT(z)) != NULL) PARENT(LEFT(y)) = y;\
            if ((PARENT(z) = PARENT(x)) != NULL)\
                if (LEFT(PARENT(x)) == x) LEFT(PARENT(z)) = z;\
                else RIGHT(PARENT(z)) = z;\
            PARENT(x) = z; RIGHT(z) = x;

/*
 * Delete a tree element
 */
static void
t_delete(TREE *op)
{
    TREE    *tp, *sp, *gp;

    /* if this is a non-tree node */
    if (ISNOTREE(op)) {
        tp = LINKBAK(op);
        if ((sp = LINKFOR(op)) != NULL)
            LINKBAK(sp) = tp;
        LINKFOR(tp) = sp;
        return;
    }

    /* make op the root of the tree */
    if (PARENT(op))
        t_splay(op);

    /* if this is the start of a list */
    if ((tp = LINKFOR(op)) != NULL) {
        PARENT(tp) = NULL;
        if ((sp = LEFT(op)) != NULL)
            PARENT(sp) = tp;
        LEFT(tp) = sp;

        if ((sp = RIGHT(op)) != NULL)
            PARENT(sp) = tp;
        RIGHT(tp) = sp;

        Root = tp;
        return;
    }

    /* if op has a non-null left subtree */
    if ((tp = LEFT(op)) != NULL) {
        PARENT(tp) = NULL;

        if (RIGHT(op)) {
            /* make the right-end of the left subtree its root */
            while ((sp = RIGHT(tp)) != NULL) {
                if ((gp = RIGHT(sp)) != NULL) {
                    TDLEFT2(tp, sp, gp);
                    tp = gp;
                } else {
                    LEFT1(tp, sp);
                    tp = sp;
                }
            }

            /* hook the right subtree of op to the above elt */
            RIGHT(tp) = RIGHT(op);
            PARENT(RIGHT(tp)) = tp;
        }
    } else if ((tp = RIGHT(op)) != NULL)    /* no left subtree */
        PARENT(tp) = NULL;

    Root = tp;
}

/*
 * Bottom up splaying (simple version).
 * The basic idea is to roughly cut in half the
 * path from Root to tp and make tp the new root.
 */
static void
t_splay(TREE *tp)
{
    TREE    *pp, *gp;

    /* iterate until tp is the root */
    while ((pp = PARENT(tp)) != NULL) {
        /* grandparent of tp */
        gp = PARENT(pp);

        /* x is a left child */
        if (LEFT(pp) == tp) {
            if (gp && LEFT(gp) == pp) {
                BURIGHT2(gp, pp, tp);
            } else {
                RIGHT1(pp, tp);
            }
        } else {
            ASSERT(RIGHT(pp) == tp);
            if (gp && RIGHT(gp) == pp) {
                BULEFT2(gp, pp, tp);
            } else {
                LEFT1(pp, tp);
            }
        }
    }
}


/*
 *  free().
 *  Performs a delayed free of the block pointed to
 *  by old. The pointer to old is saved on a list, flist,
 *  until the next malloc or realloc. At that time, all the
 *  blocks pointed to in flist are actually freed via
 *  realfree(). This allows the contents of free blocks to
 *  remain undisturbed until the next malloc or realloc.
 */
void
free(void *old)
{
    if (!primary_link_map) {
        errno = ENOTSUP;
        return;
    }
    assert_no_libc_locks_held();
    (void) mutex_lock(&libc_malloc_lock);
    _free_unlocked(old);
    (void) mutex_unlock(&libc_malloc_lock);
}


void
_free_unlocked(void *old)
{
    int i;

    if (old == NULL)
        return;

    /*
     * Make sure the same data block is not freed twice.
     * 3 cases are checked.  It returns immediately if either
     * one of the conditions is true.
     *  1. Last freed.
     *  2. Not in use or freed already.
     *  3. In the free list.
     */
    if (old == Lfree)
        return;
    if (!ISBIT0(SIZE(BLOCK(old))))
        return;
    for (i = 0; i < freeidx; i++)
        if (old == flist[i])
            return;

    if (flist[freeidx] != NULL)
        realfree(flist[freeidx]);
    flist[freeidx] = Lfree = old;
    freeidx = (freeidx + 1) & FREEMASK; /* one forward */
}

/*
 * cleanfree() frees all the blocks pointed to be flist.
 *
 * realloc() should work if it is called with a pointer
 * to a block that was freed since the last call to malloc() or
 * realloc(). If cleanfree() is called from realloc(), ptr
 * is set to the old block and that block should not be
 * freed since it is actually being reallocated.
 */
static void
cleanfree(void *ptr)
{
    char    **flp;

    flp = (char **)&(flist[freeidx]);
    for (;;) {
        if (flp == (char **)&(flist[0]))
            flp = (char **)&(flist[FREESIZE]);
        if (*--flp == NULL)
            break;
        if (*flp != ptr)
            realfree(*flp);
        *flp = NULL;
    }
    freeidx = 0;
    Lfree = NULL;
}