name : thread-safety.rst .. _thread-safety: Thread Safety ============= Per `libcurl thread safety documentation`_, libcurl is thread-safe but has no internal thread synchronization. For Python programs using PycURL, this means: * Accessing the same PycURL object from different threads is OK when this object is not involved in active transfers, as Python internally has a Global Interpreter Lock and only one operating system thread can be executing Python code at a time. * Accessing a PycURL object that is involved in an active transfer from Python code *inside a libcurl callback for the PycURL object in question* is OK, because PycURL takes out the appropriate locks. * Accessing a PycURL object that is involved in an active transfer from Python code *outside of a libcurl callback for the PycURL object in question* is unsafe. PycURL handles the necessary SSL locks for OpenSSL/LibreSSL, GnuTLS and NSS. A special situation exists when libcurl uses the standard C library name resolver (i.e., not threaded nor c-ares resolver). By default libcurl uses signals for timeouts with the C library resolver, and signals do not work properly in multi-threaded programs. When using PycURL objects from multiple Python threads ``NOSIGNAL`` option `must be given`_. .. _libcurl thread safety documentation: https://curl.haxx.se/libcurl/c/threadsafe.html .. _must be given: https://github.com/curl/curl/issues/1003