malloc_state
malloc_state/*Initialize a malloc_state struct.
This is called only from within malloc_consolidate, which needs
be called in the same contexts anyway.It is never called directly
outside of malloc_consolidate because some optimizing compilers try
to inline it at all call points, which turns out not to be an
optimization at all. (Inlining it in malloc_consolidate is fine though.)
*/
static void malloc_init_state(mstate av) {
int i;
mbinptr bin;
/* Establish circular links for normal bins */
for (i = 1; i < NBINS; ++i) {
bin = bin_at(av, i);
bin->fd = bin->bk = bin;
}
#if MORECORE_CONTIGUOUS
if (av != &main_arena)
#endif
set_noncontiguous(av);
if (av == &main_arena) set_max_fast(DEFAULT_MXFAST);
// 设置 flags 标记目前没有fast chunk
av->flags |= FASTCHUNKS_BIT;
// 就是 unsorted bin
av->top = initial_top(av);
}
malloc_consolidate该函数主要有两个功能
[*]若 fastbin 未初始化，即 global_max_fast 为 0，那就初始化 malloc_state。
[*]如果已经初始化的话，就合并 fastbin 中的 chunk。
基本的流程如下初始static void malloc_consolidate(mstate av) {
mfastbinptr *fb; /* current fastbin being consolidated */
mfastbinptr *maxfb; /* last fastbin (for loop control) */
mchunkptr p; /* current chunk being consolidated */
mchunkptr nextp; /* next chunk to consolidate */
mchunkptr unsorted_bin; /* bin header */
mchunkptr first_unsorted; /* chunk to link to */
/* These have same use as in free() */
mchunkptr nextchunk;
INTERNAL_SIZE_T size;
INTERNAL_SIZE_T nextsize;
INTERNAL_SIZE_T prevsize;
int nextinuse;
mchunkptr bck;
mchunkptr fwd;
合并chunk /*
If max_fast is 0, we know that av hasn't
yet been initialized, in which case do so below
*/
// 说明 fastbin 已经初始化
if (get_max_fast() != 0) {
// 清空 fastbin 标记
// 因为要合并 fastbin 中的 chunk 了。
clear_fastchunks(av);
//
unsorted_bin = unsorted_chunks(av);
/*
Remove each chunk from fast bin and consolidate it, placing it
then in unsorted bin. Among other reasons for doing this,
placing in unsorted bin avoids needing to calculate actual bins
until malloc is sure that chunks aren't immediately going to be
reused anyway.
*/
// 按照 fd 顺序遍历 fastbin 的每一个 bin，将 bin 中的每一个 chunk 合并掉。
maxfb = &fastbin(av, NFASTBINS - 1);
fb = &fastbin(av, 0);
do {
p = atomic_exchange_acq(fb, NULL);
if (p != 0) {
do {
check_inuse_chunk(av, p);
nextp = p->fd;
/* Slightly streamlined version of consolidation code in
* free() */
size = chunksize(p);
nextchunk = chunk_at_offset(p, size);
nextsize= chunksize(nextchunk);
if (!prev_inuse(p)) {
prevsize = prev_size(p);
size += prevsize;
p = chunk_at_offset(p, -((long) prevsize));
unlink(av, p, bck, fwd);
}
if (nextchunk != av->top) {
// 判断 nextchunk 是否是空闲的。
nextinuse = inuse_bit_at_offset(nextchunk, nextsize);
if (!nextinuse) {
size += nextsize;
unlink(av, nextchunk, bck, fwd);
} else
// 设置 nextchunk 的 prev inuse 为0，以表明可以合并当前 fast chunk。
clear_inuse_bit_at_offset(nextchunk, 0);
first_unsorted = unsorted_bin->fd;
unsorted_bin->fd = p;
first_unsorted->bk = p;
if (!in_smallbin_range(size)) {
p->fd_nextsize = NULL;
p->bk_nextsize = NULL;
}
set_head(p, size | PREV_INUSE);
p->bk = unsorted_bin;
p->fd = first_unsorted;
set_foot(p, size);
}
else {
size += nextsize;
set_head(p, size | PREV_INUSE);
av->top = p;
}
} while ((p = nextp) != 0);
}
} while (fb++ != maxfb);
初始化说明 fastbin 还没有初始化。 } else {
malloc_init_state(av);
// 在非调试情况下没有什么用，在调试情况下，做一些检测。
check_malloc_state(av);
}
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