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libpbd: fix an important thinko for cross-thread signal architecture

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The old code assumed that the thread that created a request buffer for a given
signal-emitting thread would be the latter thread, and thus a thread-local
pointer to the request buffer could be used. This turns out not to be true: the
GUI thread tends to be responsible for constructing the request buffers for
pre-registered threads.

That mechanism has been replaced by using a RWLock protected map using
pthread_t as the key and the request buffer as the value. This allows any
thread to create and register the request buffers used between any other pair
of threads (because the lookup always uses a pthread_t).

The symptoms of this problem were a signal emitted in an audioengine thread
that was propagated to the target thread, but when the target thread scans its
request buffers for requests, it finds nothing (because it didn't know about
the request buffer). In a sense, the signal was successfully delivered to the
target thread, but no meaningful work (i.e the signal handler) is performed.
This commit is contained in:
Paul Davis 2023-04-21 12:02:22 -06:00
parent 6eec11e50e
commit 5d023b4c60
7 changed files with 52 additions and 45 deletions
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4
session_utils/common.cc
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@ -103,11 +103,11 @@ class MyEventLoop : public sigc::trackable, public EventLoop
return true;
}
Glib::Threads::Mutex& slot_invalidation_mutex() { return request_buffer_map_lock; }
Glib::Threads::RWLock& slot_invalidation_rwlock() { return request_buffer_map_lock; }
private:
Glib::Threads::Thread* run_loop_thread;
Glib::Threads::Mutex request_buffer_map_lock;
Glib::Threads::RWLock request_buffer_map_lock;
};
static MyEventLoop *event_loop;