wehub-resource-sync
68 lines
2.0 KiB
Markdown
68 lines
2.0 KiB
Markdown
# Multi-threading
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Perspective's API is thread-safe, so methods may be called from different
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threads without additional consideration for safety/exclusivity/correctness. All
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`perspective.Client` and `perspective.Server` API methods release the GIL, which
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can be exploited for parallelism.
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Interally, `perspective.Server` also dispatches to a thread pool for some
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operations, enabling better parallelism and overall better query performance.
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This independent threadpool size can be controlled via
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`perspective.set_num_cpus()`, or the `OMP_NUM_THREADS` environment variable.
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```python
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import perspective
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perspective.set_num_cpus(2)
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```
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## Server handlers
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Perspective's server handler implementations each take an optional `executor`
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constructor argument, which (when provided) will configure the handler to
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process WebSocket `Client` requests on a thread pool.
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```python
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from concurrent.futures import ThreadPoolExecutor
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from tornado.web import Application
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from perspective.handlers.tornado import PerspectiveTornadoHandler
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from perspective import Server
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args = {"perspective_server": Server(), "executor": ThreadPoolExecutor()}
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app = Application(
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[
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(r"/websocket", PerspectiveTornadoHandler, args),
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# ...
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]
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)
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```
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## `on_poll_request`
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`on_poll_request` is an optional keyword argument for `Server()`, which which
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can be applied in cases where overlapping `Table.update` calls can be safely
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deferred.
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When providing a callback function to `on_poll_request`, the `Server` will
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invoke your callback when there are updates that need to be flushed, after which
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you must _eventually_ call `Server.poll` (or else no updates will be processed).
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The exact implementation of `on_poll_request` will depend on the context. A
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simple example which batches calls via `threading.Lock`:
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```python
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lock = threading.Lock()
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def on_poll_request(perspective_server):
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if lock.acquire(blocking=False):
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try:
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perspective_server.poll()
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finally:
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lock.release()
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server = Server(on_poll_request=on_poll_request)
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```
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