[Libguestfs] [PATCH nbdkit 3/4] python: Allow thread model to be set from Python code.

Thanks: Nir Soffer. --- plugins/python/nbdkit-python-plugin.pod | 26 +++++++++++++++------- plugins/python/python.c | 29 ++++++++++++++++++++++++- 2 files changed, 46 insertions(+), 9 deletions(-) diff --git a/plugins/python/nbdkit-python-plugin.pod b/plugins/python/nbdkit-python-plugin.pod index 852366f0..edd56d13 100644 --- a/plugins/python/nbdkit-python-plugin.pod +++ b/plugins/python/nbdkit-python-plugin.pod @@ -163,6 +163,15 @@ There are no arguments or return value. There are no arguments or return value. +=item C<thread_model> + +(Optional, nbdkit E<ge> 1.22) + + def thread_model(): + return nbdkit.THEAD_MODEL_SERIALIZE_ALL_REQUESTS + +See L</Threads> below. + =item C<get_ready> (Optional) @@ -367,10 +376,6 @@ optionally using C<nbdkit.set_error> first. These are not needed because you can just use ordinary Python constructs. -=item Missing: C<thread_model> - -See L</Threads> below. - =item Missing: C<name>, C<version>, @@ -387,10 +392,15 @@ These are not yet supported. =head2 Threads -The thread model for Python callbacks currently cannot be set from -Python. It is hard-coded in the C part to -C<NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS>. This may change or be -settable in future. +The thread model for Python callbacks defaults to +C<NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS>. Since S<nbdkit 1.22> +it is possible to set this by implementing a C<thread_model> function +which returns one of the constants C<nbdkit.THREAD_MODEL_*>. + +The Python Global Interpreter Lock (GIL) usually means that you cannot +execute Python code in parallel, but Python code which calls into +libraries which block (eg. to make HTTP requests) might be executed in +parallel. =head1 FILES diff --git a/plugins/python/python.c b/plugins/python/python.c index 229a46f1..398473f5 100644 --- a/plugins/python/python.c +++ b/plugins/python/python.c @@ -494,6 +494,28 @@ py_config_complete (void) return 0; } +static int +py_thread_model (void) +{ + ACQUIRE_PYTHON_GIL_FOR_CURRENT_SCOPE; + PyObject *fn; + PyObject *r; + int ret = NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS; + + if (script && callback_defined ("thread_model", &fn)) { + PyErr_Clear (); + + r = PyObject_CallObject (fn, NULL); + Py_DECREF (fn); + if (check_python_failure ("thread_model") == -1) + return -1; + ret = PyLong_AsLong (r); + Py_DECREF (r); + } + + return ret; +} + static int py_get_ready (void) { @@ -1002,7 +1024,11 @@ py_can_cache (void *handle) "script=<FILENAME> (required) The Python plugin to run.\n" \ "[other arguments may be used by the plugin that you load]" -#define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS +/* This is the maximum possible, but the default for plugins is + * NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS. Plugins can override + * that by providing a thread_model() function. + */ +#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL static struct nbdkit_plugin plugin = { .name = "python", @@ -1016,6 +1042,7 @@ static struct nbdkit_plugin plugin = { .config_complete = py_config_complete, .config_help = py_config_help, + .thread_model = py_thread_model, .get_ready = py_get_ready, .open = py_open, -- 2.27.0