rt: fix Runtime::reactor() as used by tokio-core
#721
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Up until Tokio v0.1.11, the handle returned by `Runtime::reactor()` pointed to a reactor instance running in a background thread. The thread was eagerly spawned. As of v0.1.12, a reactor instance is created per runtime worker thread. `Runtime::reactor()` was deprecated and updated to point to the reactor for one of the worker threads. A problem occurs when attempting to use the reactor before spawning a task. Worker threads are spawned lazily, which means that the reactor referenced by `Runtime::reactor()` is not yet running. This patch changes `Runtime::reactor` back to a dedicated reactor running on a background thread. However, the background thread is now spawned lazily when the deprecated function is first called. Fixes #720
ghost
approved these changes
Oct 24, 2018
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LGTM.
Just one question: would you prefer to change the Runtime and ThreadPool builders so that all worker threads and reactors are initialized immediately at construction rather than lazily on demand? In all practical cases, they should eventually spin up anyway and I imagine initializing them immediately might simplify some things besides this PR...
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@stjepang I considered it, but this seemed simpler to get done. The bug was exposed by tokio-core. Eagerly spawning all worker threads would also result in a lot of idle threads in the common case where no tasks are ever spawned. At the end of the day, this is just a work around until we delete the code in 0.2. |
Co-Authored-By: carllerche <me@carllerche.com>
ghost
merged commit 
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Nice! Thanks for the fast fix :) |
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Up until Tokio v0.1.11, the handle returned by
Runtime::reactor()pointed to a reactor instance running in a background thread. The thread
was eagerly spawned.
As of v0.1.12, a reactor instance is created per runtime worker thread.
Runtime::reactor()was deprecated and updated to point to the reactorfor one of the worker threads.
A problem occurs when attempting to use the reactor before spawning a
task. Worker threads are spawned lazily, which means that the reactor
referenced by
Runtime::reactor()is not yet running.This patch changes
Runtime::reactorback to a dedicated reactorrunning on a background thread. However, the background thread is now
spawned lazily when the deprecated function is first called.
Fixes #720