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threaded-resolver: fix shutdown

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Changed strategy to start up and terminate resolver thread.

When starting up:

Start the thread with mutex acquired, wait for signal from thread that
it started and has incremented the ref counter. Thread set
pthread_cancel() to disabled before that and only enables cancelling
during resolving itself. This assure that the ref counter is correct and
the unlinking of the resolve context always happens.

When shutting down resolving:

If ref counting shows thread has finished, join it, free everything. If
thread has not finished, try pthread_cancel() (non Windows), but keep
the thread handle around.

When destroying resolving:

Shutdown first, then, if the thread is still there and 'quick_exit' is
not set, join it and free everything. This might occur a delay if
getaddrinfo() hangs and cannot be interrupted by pthread_cancel().

Destroying resolving happens when another resolve is started on an
easy handle or when the easy handle is closed.

Add test795 to check that connect timeout triggers correctly
when resolving is delayed. Add debug env var `CURL_DNS_DELAY_MS`
to simulate delays in resolving.

Fix test1557 to set `quick_exit` and use `xxx.invalid` as domain
instead of `nothing` that was leading to hangers in CI.

Closes #18263
This commit is contained in:
Stefan Eissing 2025-08-20 15:48:20 +02:00 • committed by Daniel Stenberg
parent f3488ee3a3
commit 88fc6c491f
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GPG key ID: 5CC908FDB71E12C2
12 changed files with 391 additions and 124 deletions
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30
lib/curl_threads.h
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@ -34,6 +34,12 @@
# define Curl_mutex_acquire(m) pthread_mutex_lock(m)
# define Curl_mutex_release(m) pthread_mutex_unlock(m)
# define Curl_mutex_destroy(m) pthread_mutex_destroy(m)
# define USE_CURL_COND_T
# define curl_cond_t pthread_cond_t
# define Curl_cond_init(c) pthread_cond_init(c, NULL)
# define Curl_cond_destroy(c) pthread_cond_destroy(c)
# define Curl_cond_wait(c, m) pthread_cond_wait(c, m)
# define Curl_cond_signal(c) pthread_cond_signal(c)
#elif defined(USE_THREADS_WIN32)
# define CURL_STDCALL __stdcall
# define curl_mutex_t CRITICAL_SECTION
@ -47,6 +53,14 @@
# define Curl_mutex_acquire(m) EnterCriticalSection(m)
# define Curl_mutex_release(m) LeaveCriticalSection(m)
# define Curl_mutex_destroy(m) DeleteCriticalSection(m)
# if defined(_WIN32_WINNT) && (_WIN32_WINNT >= _WIN32_WINNT_VISTA)
# define USE_CURL_COND_T
# define curl_cond_t CONDITION_VARIABLE
# define Curl_cond_init(c) InitializeConditionVariable(c)
# define Curl_cond_destroy(c) (void)(c)
# define Curl_cond_wait(c, m) SleepConditionVariableCS(c, m, INFINITE)
# define Curl_cond_signal(c) WakeConditionVariable(c)
# endif
#else
# define CURL_STDCALL
#endif
@ -66,6 +80,22 @@ void Curl_thread_destroy(curl_thread_t *hnd);
int Curl_thread_join(curl_thread_t *hnd);
int Curl_thread_cancel(curl_thread_t *hnd);
#if defined(USE_THREADS_POSIX) && defined(PTHREAD_CANCEL_ENABLE)
#define Curl_thread_push_cleanup(a,b) pthread_cleanup_push(a,b)
#define Curl_thread_pop_cleanup() pthread_cleanup_pop(0)
#define Curl_thread_enable_cancel() \
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL)
#define Curl_thread_disable_cancel() \
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL)
#else
#define Curl_thread_push_cleanup(a,b) ((void)a,(void)b)
#define Curl_thread_pop_cleanup() Curl_nop_stmt
#define Curl_thread_enable_cancel() Curl_nop_stmt
#define Curl_thread_disable_cancel() Curl_nop_stmt
#endif
#endif /* USE_THREADS_POSIX || USE_THREADS_WIN32 */
#endif /* HEADER_CURL_THREADS_H */