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curl hangs at 100% cpu usage on http/1.1 concurrent request with pipewait=1 #3813

TvdW opened this issue Apr 29, 2019 · 0 comments


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TvdW commented Apr 29, 2019

Initially found this as a bug on 7.64.1, where curl with CURLOPT_PIPEWAIT and CURLMOPT_MULTIPLEX on a HTTP/1.1 server would fail to execute requests concurrently until the second batch of requests were scheduled. However, the behavior seems to have gotten worse on the latest master, and now results in a curl hang at 100% CPU usage.


#include "curl/curl.h"

int main(int argc, char** argv)
    CURLM *multi = curl_multi_init();
    curl_multi_setopt(multi, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
    curl_multi_setopt(multi, CURLMOPT_MAX_HOST_CONNECTIONS, 4);

    int i;
    for (i = 0; i < 5; i++) {
        CURL *easy = curl_easy_init();
        curl_easy_setopt(easy, CURLOPT_URL, "");
        curl_easy_setopt(easy, CURLOPT_VERBOSE, 1);
        curl_easy_setopt(easy, CURLOPT_PIPEWAIT, 1);
        curl_easy_setopt(easy, CURLOPT_NOPROXY, "");
        curl_easy_setopt(easy, CURLOPT_PROXY, "http://my-http-proxy:3128");

        curl_multi_add_handle(multi, easy);

    int running= 1;
    while (running) {
        int numfds;
        curl_multi_perform(multi, &running);
        curl_multi_wait(multi, NULL, 0, 1000, &numfds);


    return 0;

On 7.64.1, this will take ~10 seconds to run. On master, this hangs.

* Connection #0 to host my-http-proxy left intact
* Found bundle for host 0x1b99f00 [serially]
* Server doesn't support multiplex yet, wait
* No connections available.
@bagder bagder added the HTTP label Apr 29, 2019
@bagder bagder self-assigned this Apr 29, 2019
@bagder bagder closed this as completed in c32248f May 1, 2019
@lock lock bot locked as resolved and limited conversation to collaborators Jul 30, 2019
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2 participants