fix race condition in service plugin loading#7968
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whummer
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Mar 25, 2023
localstack/services/plugins.py
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| return None | ||
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| with self._mutex: | ||
| if plugin.service.name() not in self._services: |
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Wondering if there can be a situation where this condition is not true, i.e., where an entry for this service name would already exist in self._services (since we're now locking on the service name in this critical section, and _load_service_plugin(..) in line 565 above is side-effect free).
The only case where this could happen is if plugin.service.name() returns a string that is different from name - can this be the case?
If that's something we're not expecting to happen, maybe we could proactively raise an error, to avoid such cases from going unnoticed:
with self._mutex:
service_name = plugin.service.name()
if service_name in self._services:
raise ServiceStateException(
"Service {service_name} unexpectedly already in list of loaded services")
)
super().add_service(plugin.service)
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good point, can't happen anymore. fixed!
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This PR fixes a race condition in the service plugin loading, where multiple concurrent calls to
service_manager.require(...)could lead to Service plugins being instantiated more than once, and subsequentlyon_after_initbeing called multiple times, whose implementation often mutates global state.We haven't seen this manifest yet, other an exception in the logs when running
tests/integration/test_terraform.py::TestTerraform::test_bucket_exists:which was an obscure indicator that
on_after_initwas called twice.The PR introduces a locking mechanism that makes sure that, while the service is being loaded and instantiated, other calls to
requireof the same service block. TheSynchronizedDefaultDict(RLock)pattern is helpful here - and we make sure we delete the locks after using them (we only need them once).