`LocalSet` cleans up any tasks that have not yet been completed when it is
dropped. Previously, this cleanup process required access to a thread-local.
Suppose a `LocalSet` is stored in a thread-local itself. In that case, when it is
dropped, there is no guarantee the drop implementation will be able to
access the internal `LocalSet` thread-local as it may already have been
destroyed.
The internal `LocalSet` thread local is mainly used to avoid writing unsafe
code. All `LocalState` that cannot be moved across threads is stored in the
thread-local and accessed on demand.
This patch moves this local-only state into the `LocalSet`'s "shared" struct.
Because this struct *is* `Send`, the local-only state is stored in `UnsafeCell`,
and callers must ensure not to touch it from other threads.
A debug assertion is added to enforce this requirement in tests.
Fixes#5162
An earlier change updated `enter_runtime` to also set the current
handle. However, the change did not store the `SetCurrentGuard`, so the
"current handle" was immediately unset. This patch stores the
`SetCurrentGuard` in the `EnterRuntimeGuard`.
No existing test exposed this bug because all tests went via `Runtime`
instead of `Handle`. Currently, `Runtime` is still explicitly setting
the handle before entering runtime, so all tests still passed. A new
test is added that covers the case of calling `Handle::block_on` and
accessing the current handle.
A previous patch moved code related to entering a runtime into the
context module but did not change anything. This patch combines both
thread-local variables.
This moves the functions, types, and thread-local related to entering a
runtime into the context module. This does not yet unify the thread-local
variables, as that, will be done in a follow-up PR.
Instead of each scheduler flavor holding a reference to the scheduler
handle, the scheduler handle is passed in as needed. This removes a
duplicate handle reference in the `Runtime` struct and lays the
groundwork for further handle struct tweaks.
Publish the blocking thread pool metrics as thread-safe values, written
under the blocking thread pool's lock and able to be read in a lock-free
fashion by any reader.
Fixes#5156
This is a first step towards unifying the concepts of "entering a
runtime" and setting `Handle::current`.
Previously, these two operations were performed separately at each call
site (runtime block_on, ...). This is error-prone and also requires
multiple accesses to the thread-local variable. Additionally, "entering
the runtime" conflated the concept of entering a blocking region. For
example, calling `mpsc::Receiver::recv_blocking` performed the "enter
the runtime" step. This was done to prevent blocking a runtime, as the
operation will panic when called from an existing runtime.
To untangle these concepts, the patch splits out each logical operation
into functions. In total, there are three "enter" operations:
* `set_current_handle`
* `enter_runtime`
* `enter_blocking_region`
There are some behavior changes with each function, but they
should not translate to public behavior changes. The most significant is
`enter_blocking_region` does not change the value of the thread-local
variable, which means the function can be re-entered. Since
`enter_blocking_region` is an internal-only function and we do not
re-enter, this has no public-facing impact.
Because `enter_runtime` takes a `&Handle` to combine the
`set_current_handle` operation with entering a runtime, the patch
exposes an annoyance with the current `scheduler::Handle` struct layout.
A new instance of `scheduler::Handle` must be constructed at each call
to `enter_runtime`. We can explore cleaning this up later.
This patch also does not combine the "entered runtime" thread-local
variable with the "context" thread-local variable. To keep the patch
smaller, this has been punted to a follow-up change.
This patch consolidates the budget thread-local state with the
`runtime::context` thread local. This reduces the number of thread-local
variables used by Tokio by one.
The `LocalSet::run_until` future is just a "plain" future that should
run on a runtime that already has a coop budget. In other words, the
`run_until` future should not get its own budget but should inherit the
calling task's budget. Getting this behavior is done by removing the
call to `budget` in `run_until`.
This is a step towards unifying thread-local variables. In the future,
`coop` will be updated to use the runtime context thread-local to store
its state.
This patch does some internal renames to remove some confusion.
* `allow_blocking` is renamed to `allow_block_in_place` to indicate that
the variable only impacts the `block_in_place()` function.
* `context::try_enter` is renamed to `context::try_set_current` to
disambiguate between the various "enter" functions. This function only
sets the runtime handle used by Tokio's public APIs. Entering a runtime
is a separate operation. # Please enter the commit message for your
changes.
* `scheduler::Handle::enter()` is removed to consolidate methods that
set the current context.
This patch is the first step towards unifying all the thread-local
variables spread out across Tokio. A new `Context` struct is added which
will be used to replace the various thread-locals that exist today.
Initially, `Context` only holds the current runtime handle and the
random number generator. Further PRs will add other thread-local state.
A previous PR removed `runtime::context`. At that time,
`runtime::context` was used as an extra layer to access the various
runtime driver handles. This version of `runtime::context` serves a
different purpose (unifying all the thread-locals).
While setting the random number generator seed with the multi-threaded
scheduler does result in deterministic behavior related to the random
number generator, threads still introduce non-determinism, making it
hard (impossible?) to test this. There also is little value in doing so.
This patch also updates the docs to remove mention of work stealing.
The signal driver still uses an `Arc` internally to track if the driver
is still running, however, using the `scheduler::Handle` to access the
signal driver handle lets us delete some code.
The improvement to the `rng_seed` tests added in #5075 missed a case in
the `rt_threaded` tests which was still checking for a specific value.
As described in that PR, this makes the tests fragile and changing tokio
internals may require updating the test.
This change fixes that half-implemented improvement so that the tests no
longer depend on the exact internal ordering, but rather compare two
runs of separate runtimes built with the same seed to check that the
results are the same.
