curl: initialize and cleanup global curl state #4554
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Our curl-based streams make use of the easy curl interface. This interface automatically initializes and de-initializes the global curl state by calling out to `curl_global_init` and `curl_global_cleanup`. Thus, all global state will be repeatedly re-initialized when creating multiple curl streams in succession. Despite being inefficient, this is not thread-safe due to `curl_global_init` being not thread-safe itself. Thus a multi-threaded programing handling multiple curl streams at the same time is inherently racy. Fix the issue by globally initializing and cleaning up curl's state.
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The documentation of curl states that any program making use of libcurl
is responsible for calling
curl_global_initprevious to using anycurl functions, and
curl_global_cleanupwhen the program is about toterminate. We currently call neither. While this seems to work just
fine, Valgrind may complain about unfree'd memory.
Fix the issue by correctly setting up and tearing down libcurl.
Edit for the corrected reasoning behind this PR:
Our curl-based streams make use of the easy curl interface. This
interface automatically initializes and de-initializes the global curl
state by calling out to
curl_global_initandcurl_global_cleanup.Thus, all global state will be repeatedly re-initialized when creating
multiple curl streams in succession. Despite being inefficient, this is
not thread-safe due to
curl_global_initbeing not thread-safe itself.Thus a multi-threaded programing handling multiple curl streams at the
same time is inherently racy.
Fix the issue by globally initializing and cleaning up curl's state.