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multi: xfer table/bitset, handle limits

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* calculate capacity growth on multi's xfer table and bitsets to
  work correctly when approaching UINT_MAX
* uint-bset: track the first 64bit slot used. This avoids slot scans
  on empty sets.
* uint-tbl: remove restriction to grow ot UINT_MAX, it is multi's
  job to enforce limits suitable for its use
* test751: use curl_mfprintf() for error messages

Closes #17731
This commit is contained in:
Stefan Eissing 2025-06-24 12:57:04 +02:00 • committed by Daniel Stenberg
parent 65f8253336
commit e80c893254
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5 changed files with 60 additions and 29 deletions
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63
lib/multi.c
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@ -339,35 +339,58 @@ static void multi_warn_debug(struct Curl_multi *multi, struct Curl_easy *data)
static CURLMcode multi_xfers_add(struct Curl_multi *multi,
struct Curl_easy *data)
{
/* We want `multi->xfers` to have "sufficient" free rows, so that we do
* have to reuse the `mid` from a just removed easy right away.
* Since uint_tbl and uint_bset is quite memory efficient,
* regard less than 25% free as insufficient.
* (for low capacities, e.g. multi_easy, 4 or less). */
unsigned int capacity = Curl_uint_tbl_capacity(&multi->xfers);
unsigned int unused = capacity - Curl_uint_tbl_count(&multi->xfers);
unsigned int min_unused = CURLMAX(capacity >> 2, 4);
unsigned int new_size = 0;
/* Prepare to make this into a CURLMOPT_MAX_TRANSFERS, because some
* applications may want to prevent a run-away of their memory use. */
/* UINT_MAX is our "invalid" id, do not let the table grow up to that. */
const unsigned int max_capacity = UINT_MAX - 1;
if(unused <= min_unused) {
/* make it a 64 multiple, since our bitsets frow by that and
* small (easy_multi) grows to at least 64 on first resize. */
unsigned int newsize = (((capacity + min_unused) + 63) / 64) * 64;
DEBUGASSERT(newsize > capacity);
if(capacity < max_capacity) {
/* We want `multi->xfers` to have "sufficient" free rows, so that we do
* have to reuse the `mid` from a just removed easy right away.
* Since uint_tbl and uint_bset are quite memory efficient,
* regard less than 25% free as insufficient.
* (for low capacities, e.g. multi_easy, 4 or less). */
unsigned int used = Curl_uint_tbl_count(&multi->xfers);
unsigned int unused = capacity - used;
unsigned int min_unused = CURLMAX(capacity >> 2, 4);
if(unused <= min_unused) {
/* Make sure the uint arithmetic here works on the corner
* cases where we are close to max_capacity or UINT_MAX */
if((min_unused >= max_capacity) ||
((max_capacity - min_unused) <= capacity) ||
((UINT_MAX - min_unused - 63) <= capacity)) {
new_size = max_capacity; /* can not be larger than this */
}
else {
/* make it a 64 multiple, since our bitsets frow by that and
* small (easy_multi) grows to at least 64 on first resize. */
new_size = CURLMIN((((used + min_unused) + 63) / 64) * 64,
max_capacity);
}
}
}
if(new_size > capacity) {
/* Grow the bitsets first. Should one fail, we do not need
* to downsize the already resized ones. The sets continue
* to work properly when larger than the table, but not
* the other way around. */
if(Curl_uint_bset_resize(&multi->process, newsize) ||
Curl_uint_bset_resize(&multi->dirty, newsize) ||
Curl_uint_bset_resize(&multi->pending, newsize) ||
Curl_uint_bset_resize(&multi->msgsent, newsize) ||
Curl_uint_tbl_resize(&multi->xfers, newsize))
CURL_TRC_M(data, "increasing xfer table size to %u", new_size);
if(Curl_uint_bset_resize(&multi->process, new_size) ||
Curl_uint_bset_resize(&multi->dirty, new_size) ||
Curl_uint_bset_resize(&multi->pending, new_size) ||
Curl_uint_bset_resize(&multi->msgsent, new_size) ||
Curl_uint_tbl_resize(&multi->xfers, new_size))
return CURLM_OUT_OF_MEMORY;
CURL_TRC_M(data, "increased xfer table size to %u", newsize);
}
/* Insert the easy into the table now that MUST have room for it */
/* Insert the easy into the table now */
if(!Curl_uint_tbl_add(&multi->xfers, data, &data->mid)) {
DEBUGASSERT(0);
/* MUST only happen when table is full */
DEBUGASSERT(Curl_uint_tbl_capacity(&multi->xfers) <=
Curl_uint_tbl_count(&multi->xfers));
return CURLM_OUT_OF_MEMORY;
}
return CURLM_OK;