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39036c9021
Use a thread queue and pool for asnyc threaded DNS resolves. Add pytest test_21_* for verification. Add `CURLMOPT_RESOLVE_THREADS_MAX` to allow applications to resize the thread pool used. Add `CURLMOPT_QUICK_EXIT` to allow applications to skip thread joins when cleaning up a multi handle. Multi handles in `curl_easy_perform()` inherit this from `CURLOPT_QUICK_EXIT`. Add several debug environment variables for testing. Closes #20936
75 lines
1.9 KiB
Markdown
75 lines
1.9 KiB
Markdown
---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLMOPT_RESOLVE_THREADS_MAX
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_IPRESOLVE (3)
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- CURLOPT_RESOLVE (3)
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Protocol:
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- All
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Added-in: 8.20.0
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---
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# NAME
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CURLMOPT_RESOLVE_THREADS_MAX - max threads for threaded DNS resolver
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_RESOLVE_THREADS_MAX,
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long amount);
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~~~
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# DESCRIPTION
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Pass a long for the **amount**. The set number is used as the maximum number
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of threads to be used for the threaded DNS resolver. It has to be a
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positive number in the range of 32 bits.
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When libcurl is built with a threaded resolver, which is the default on
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many systems, it uses a thread pool to lookup addresses and other
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properties of hostnames so other transfers are not blocked by this.
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Threads are started on demand to perform the resolving and shut down
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again after a period of inactivity. When the maximum number of threads
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is reached, outstanding resolves are held in a queue and served when
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a thread becomes available.
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The default maximum is expected to work fine for many situations. Application
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may override it using this option for the multi handle.
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Changing this value while there are resolves in progress is possible.
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Increasing the value takes effect right away. Lowering the value does
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not close down any resolves, but ends threads above the new maximum
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once the resolving is done.
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# DEFAULT
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20.
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# %PROTOCOLS%
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# EXAMPLE
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~~~c
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int main(void)
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{
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CURLM *m = curl_multi_init();
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/* never use more than 5 threads for resolving */
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curl_multi_setopt(m, CURLMOPT_RESOLVE_THREADS_MAX, 5L);
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}
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~~~
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# %AVAILABILITY%
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# RETURN VALUE
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curl_multi_setopt(3) returns a CURLMcode indicating success or error.
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CURLM_OK (0) means everything was OK, non-zero means an error occurred, see
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libcurl-errors(3).
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