The green scheduler can optimize its runtime based on this by deciding to not go
to sleep in epoll() if there is no active I/O and there is a task to be stolen.
This is implemented for librustuv by keeping a count of the number of tasks
which are currently homed. If a task is homed, and then performs a blocking I/O
operation, the count will be nonzero while the task is blocked. The homing count
is intentionally 0 when there are I/O handles, but no handles currently blocked.
The reason for this is that epoll() would only be used to wake up the scheduler
anyway.
The crux of this change was to have a `HomingMissile` contain a mutable borrowed
reference back to the `HomeHandle`. The rest of the change was just dealing with
this fallout. This reference is used to decrement the homed handle count in a
HomingMissile's destructor.
Also note that the count maintained is not atomic because all of its
increments/decrements/reads are all on the same I/O thread.
This, the Nth rewrite of channels, is not a rewrite of the core logic behind
channels, but rather their API usage. In the past, we had the distinction
between oneshot, stream, and shared channels, but the most recent rewrite
dropped oneshots in favor of streams and shared channels.
This distinction of stream vs shared has shown that it's not quite what we'd
like either, and this moves the `std::comm` module in the direction of "one
channel to rule them all". There now remains only one Chan and one Port.
This new channel is actually a hybrid oneshot/stream/shared channel under the
hood in order to optimize for the use cases in question. Additionally, this also
reduces the cognitive burden of having to choose between a Chan or a SharedChan
in an API.
My simple benchmarks show no reduction in efficiency over the existing channels
today, and a 3x improvement in the oneshot case. I sadly don't have a
pre-last-rewrite compiler to test out the old old oneshots, but I would imagine
that the performance is comparable, but slightly slower (due to atomic reference
counting).
This commit also brings the bonus bugfix to channels that the pending queue of
messages are all dropped when a Port disappears rather then when both the Port
and the Chan disappear.
* vec::raw::to_ptr is gone
* Pausible => Pausable
* Removing @
* Calling the main task "<main>"
* Removing unused imports
* Removing unused mut
* Bringing some libextra tests up to date
* Allowing compiletest to work at stage0
* Fixing the bootstrap-from-c rmake tests
* assert => rtassert in a few cases
* printing to stderr instead of stdout in fail!()
The uv loop was being destroyed before the async handle was being destroyed, so
closing the async handle was causing a use-after-free in the uv loop. This was
fixed by moving destruction of the queue's async handle to an earlier location
and then actually freeing it once the loop has been dropped.
The queue has an async handle which must be destroyed before the loop is
destroyed, so use a little bit of an option dance to get around this
requirement.
This allows creation of different sched pools with different io factories.
Namely, this will be used to test the basic I/O loop in the green crate. This
can also be used to override the global default.
All tests except for the homing tests are now working again with the
librustuv/libgreen refactoring. The homing-related tests are currently commented
out and now placed in the rustuv::homing module.
I plan on refactoring scheduler pool spawning in order to enable more homing
tests in a future commit.
This reimplements librustuv without using the interfaces provided by the
scheduler in libstd. This solely uses the new Runtime trait in order to
interface with the local task and perform the necessary scheduling operations.
The largest snag in this refactoring is reimplementing homing. The new runtime
trait exposes no concept of "homing" a task or forcibly sending a task to a
remote scheduler (there is no concept of a scheduler). In order to reimplement
homing, the transferrence of tasks is now done at the librustuv level instead of
the scheduler level. This means that all I/O loops now have a concurrent queue
which receives homing messages and requests.
This allows the entire implementation of librustuv to be only dependent on the
runtime trait, severing all dependence of librustuv on the scheduler and related
green-thread functions.
This is all in preparation of the introduction of libgreen and libnative.
At the same time, I also took the liberty of removing all glob imports from
librustuv.
The reasons for doing this are:
* The model on which linked failure is based is inherently complex
* The implementation is also very complex, and there are few remaining who
fully understand the implementation
* There are existing race conditions in the core context switching function of
the scheduler, and possibly others.
* It's unclear whether this model of linked failure maps well to a 1:1 threading
model
Linked failure is often a desired aspect of tasks, but we would like to take a
much more conservative approach in re-implementing linked failure if at all.
Closes#8674Closes#8318Closes#8863
In the ideal world, uv I/O could be canceled safely at any time. In reality,
however, we are unable to do this. Right now linked failure is fairly flaky as
implemented in the runtime, making it very difficult to test whether the linked
failure mechanisms inside of the uv bindings are ready for this kind of
interaction.
Right now, all constructors will execute in a task::unkillable block, and all
homing I/O operations will prevent linked failure in the duration of the homing
operation. What this means is that tasks which perform I/O are still susceptible
to linked failure, but the I/O operations themselves will never get interrupted.
Instead, the linked failure will be received at the edge of the I/O operation.
It turns out that the uv implementation would cause use-after-free if the idle
callback was used after the call to `close`, and additionally nothing would ever
really work that well if `start()` were called twice. To change this, the
`start` and `close` methods were removed in favor of specifying the callback at
creation, and allowing destruction to take care of closing the watcher.
This renames the `file` module to `fs` because that more accurately describes
its current purpose (manipulating the filesystem, not just files).
Additionally, this adds an UnstableFileStat structure as a nested structure of
FileStat to signify that the fields should not be depended on. The structure is
currently flagged with #[unstable], but it's unlikely that it has much meaning.
Closes#10241
This adds bindings to the remaining functions provided by libuv, all of which
are useful operations on files which need to get exposed somehow.
Some highlights:
* Dropped `FileReader` and `FileWriter` and `FileStream` for one `File` type
* Moved all file-related methods to be static methods under `File`
* All directory related methods are still top-level functions
* Created `io::FilePermission` types (backed by u32) that are what you'd expect
* Created `io::FileType` and refactored `FileStat` to use FileType and
FilePermission
* Removed the expanding matrix of `FileMode` operations. The mode of reading a
file will not have the O_CREAT flag, but a write mode will always have the
O_CREAT flag.
Closes#10130Closes#10131Closes#10121
This commit moves all thread-blocking I/O functions from the std::os module.
Their replacements can be found in either std::rt::io::file or in a hidden
"old_os" module inside of native::file. I didn't want to outright delete these
functions because they have a lot of special casing learned over time for each
OS/platform, and I imagine that these will someday get integrated into a
blocking implementation of IoFactory. For now, they're moved to a private module
to prevent bitrot and still have tests to ensure that they work.
I've also expanded the extensions to a few more methods defined on Path, most of
which were previously defined in std::os but now have non-thread-blocking
implementations as part of using the current IoFactory.
The api of io::file is in flux, but I plan on changing it in the next commit as
well.
Closes#10057
The invocation for making a directory should be able to specify a mode to make
the directory with (instead of defaulting to one particular mode). Additionally,
libuv and various OSes implement efficient versions of renaming files, so this
operation is exposed as an IoFactory call.
Cleaned up the source in a few places
Renamed `map_move` to `map`, removed other `map` methods
Added `as_ref` and `as_mut` adapters to `Result`
Added `fmt::Default` impl
There are a few reasons that this is a desirable move to take:
1. Proof of concept that a third party event loop is possible
2. Clear separation of responsibility between rt::io and the uv-backend
3. Enforce in the future that the event loop is "pluggable" and replacable
Here's a quick summary of the points of this pull request which make this
possible:
* Two new lang items were introduced: event_loop, and event_loop_factory.
The idea of a "factory" is to define a function which can be called with no
arguments and will return the new event loop as a trait object. This factory
is emitted to the crate map when building an executable. The factory doesn't
have to exist, and when it doesn't then an empty slot is in the crate map and
a basic event loop with no I/O support is provided to the runtime.
* When building an executable, then the rustuv crate will be linked by default
(providing a default implementation of the event loop) via a similar method to
injecting a dependency on libstd. This is currently the only location where
the rustuv crate is ever linked.
* There is a new #[no_uv] attribute (implied by #[no_std]) which denies
implicitly linking to rustuv by default
Closes#5019
