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share: concurrency handling, easy updates

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Replace the `volatile int dirty` with a reference counter
protected by a mutex when available.

Solve the problem of when to call application's lock function
by adding a volatile flag that indicates a share has been added
to easy handles in its lifetime. That flag ever goes from
FALSE to TRUE, so volatile might work (in the absence of a mutex).

(The problem is that the lock/unlock functions need 2-3
`curl_share_setopt()` invocations to become usable and there
is no way of telling if the third will ever happen. Calling
the lock function before the 3rd setopt may crash the
application.)

When removing a share from an easy handle (or replacing it with
another share), detach the easy connection on a share with a
connection pool.

When cleaning up a share, allow this even if it is still used in
easy handles. It will be destroyed when the reference count
drops to 0.

Closes #20870
This commit is contained in:
Stefan Eissing 2026-03-09 15:40:34 +01:00 • committed by Daniel Stenberg
parent 745344ea4e
commit 82009c4220
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GPG key ID: 5CC908FDB71E12C2
26 changed files with 378 additions and 210 deletions
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70
lib/setopt.c
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@ -1490,67 +1490,17 @@ static CURLcode setopt_pointers(struct Curl_easy *data, CURLoption option,
case CURLOPT_SHARE: {
struct Curl_share *set = va_arg(param, struct Curl_share *);
/* disconnect from old share, if any */
if(data->share) {
Curl_share_lock(data, CURL_LOCK_DATA_SHARE, CURL_LOCK_ACCESS_SINGLE);
/* disconnect from old share, if any and possible */
result = Curl_share_easy_unlink(data);
if(result)
return result;
#if !defined(CURL_DISABLE_HTTP) && !defined(CURL_DISABLE_COOKIES)
if(data->share->cookies == data->cookies)
data->cookies = NULL;
#endif
#ifndef CURL_DISABLE_HSTS
if(data->share->hsts == data->hsts)
data->hsts = NULL;
#endif
#ifdef USE_LIBPSL
if(data->psl == &data->share->psl)
data->psl = data->multi ? &data->multi->psl : NULL;
#endif
if(data->share->specifier & (1 << CURL_LOCK_DATA_DNS)) {
Curl_dns_entry_unlink(data, &data->state.dns[0]);
Curl_dns_entry_unlink(data, &data->state.dns[1]);
}
data->share->dirty--;
Curl_share_unlock(data, CURL_LOCK_DATA_SHARE);
data->share = NULL;
/* use new share if it set */
if(GOOD_SHARE_HANDLE(set)) {
result = Curl_share_easy_link(data, set);
if(result)
return result;
}
if(GOOD_SHARE_HANDLE(set))
/* use new share if it set */
data->share = set;
if(data->share) {
Curl_share_lock(data, CURL_LOCK_DATA_SHARE, CURL_LOCK_ACCESS_SINGLE);
data->share->dirty++;
#if !defined(CURL_DISABLE_HTTP) && !defined(CURL_DISABLE_COOKIES)
if(data->share->cookies) {
/* use shared cookie list, first free own one if any */
Curl_cookie_cleanup(data->cookies);
/* enable cookies since we now use a share that uses cookies! */
data->cookies = data->share->cookies;
}
#endif /* CURL_DISABLE_HTTP */
#ifndef CURL_DISABLE_HSTS
if(data->share->hsts) {
/* first free the private one if any */
Curl_hsts_cleanup(&data->hsts);
data->hsts = data->share->hsts;
}
#endif
#ifdef USE_LIBPSL
if(data->share->specifier & (1 << CURL_LOCK_DATA_PSL))
data->psl = &data->share->psl;
#endif
Curl_share_unlock(data, CURL_LOCK_DATA_SHARE);
}
/* check for host cache not needed,
* it will be done by curl_easy_perform */
break;
}
@ -2434,7 +2384,7 @@ static CURLcode setopt_cptr(struct Curl_easy *data, CURLoption option,
break;
#endif
#endif
#ifdef CURLRES_ARES
#ifdef USE_RESOLV_ARES
case CURLOPT_DNS_SERVERS:
result = Curl_setstropt(&s->str[STRING_DNS_SERVERS], ptr);
if(result)