Move task count bookeeping out of libstd #11212
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For libgreen, bookeeping should not be global but rather on a per-pool basis. Inside libnative, it's known that there must be a global counter with a mutex/cvar. The benefit of taking this strategy is to remove this functionality from libstd to allow fine-grained control of it through libnative/libgreen. Notably, helper threads in libnative can manually decrement the global count so they don't count towards the global count of threads. Also, the shutdown process of *all* sched pools is now dependent on the number of tasks in the pool being 0 rather than this only being a hardcoded solution for the initial sched pool in libgreen. This involved adding a Local::try_take() method on the Local trait in order for the channel wakeup to work inside of libgreen. The channel send was happening from a SchedTask when there is no Task available in TLS, and now this is possible to work (remote wakeups are always possible, just a little slower).
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For libgreen, bookeeping should not be global but rather on a per-pool basis. Inside libnative, it's known that there must be a global counter with a mutex/cvar. The benefit of taking this strategy is to remove this functionality from libstd to allow fine-grained control of it through libnative/libgreen. Notably, helper threads in libnative can manually decrement the global count so they don't count towards the global count of threads. Also, the shutdown process of *all* sched pools is now dependent on the number of tasks in the pool being 0 rather than this only being a hardcoded solution for the initial sched pool in libgreen. This involved adding a Local::try_take() method on the Local trait in order for the channel wakeup to work inside of libgreen. The channel send was happening from a SchedTask when there is no Task available in TLS, and now this is possible to work (remote wakeups are always possible, just a little slower).
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Initial impl of `unnecessary_first_then_check` Fixes rust-lang#11212 Checks for `{slice/vec/Box<[]>}.first().is_some()` and suggests replacing the unnecessary `Option`-construct with a direct `{slice/...}.is_empty()`. Other lints guide constructs like `if let Some(_) = v.get(0)` into this, which end up as `!v.is_empty()`. changelog: [`unnecessary_first_then_check`]: Initial implementation
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For libgreen, bookeeping should not be global but rather on a per-pool basis.
Inside libnative, it's known that there must be a global counter with a
mutex/cvar.
The benefit of taking this strategy is to remove this functionality from libstd
to allow fine-grained control of it through libnative/libgreen. Notably, helper
threads in libnative can manually decrement the global count so they don't count
towards the global count of threads. Also, the shutdown process of all sched
pools is now dependent on the number of tasks in the pool being 0 rather than
this only being a hardcoded solution for the initial sched pool in libgreen.
This involved adding a Local::try_take() method on the Local trait in order for
the channel wakeup to work inside of libgreen. The channel send was happening
from a SchedTask when there is no Task available in TLS, and now this is
possible to work (remote wakeups are always possible, just a little slower).