Sync threads on startup #1242
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Sync threads on startup #1242
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It's possible that not all threads have started by the time other threads start to serve requests. This is in particular problematic with the status handler: the `on_req_json` function relies on `on_context_init` being called for all threads, but in fact the call of `h2o_multithread_register_receiver` might be racing against the value of `self->receivers.size`. This results in more threads being called than `collector->num_remaining_threads_atomic`. A consequence of this can be that either `send_response` is not called (and the fd of the request is leaked), or on `final()` being called twice (leading to a possible double free). This commit solves the issue by introducing a synchronization point in the initialization, in order to make sure that all contexts for all threads are initialized before starting to serve requests.
We the use this to synchronize the initialization of the threads run in src/main.c, so that we don't start servicing requests before the initialization has been complete.
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Thank you for the fix and the new building block (for writing barriers). |
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It's possible that not all threads have started by the time other
threads start to serve requests.
This is in particular problematic with the status handler: the
on_req_json function relies on on_context_init being called for all
threads, but in fact the call of h2o_multithread_register_receiver
might be racing against the value of self->receivers.size.
This results in more threads being called than
collector->num_remaining_threads_atomic. A consequence of this can be
that either send_response is not called (and the fd of the request
is leaked), or on final() being called twice (leading to a possible
double free).
This commit solves the issue by introducing a barrier-like API that we use
as a synchronization point at startup time. By doing this, it's not possible
anymore that threads serve requests without all of them being initialized.