This commit revisits the `cast` module in libcore and libstd, and scrutinizes
all functions inside of it. The result was to remove the `cast` module entirely,
folding all functionality into the `mem` module. Specifically, this is the fate
of each function in the `cast` module.
* transmute - This function was moved to `mem`, but it is now marked as
#[unstable]. This is due to planned changes to the `transmute`
function and how it can be invoked (see the #[unstable] comment).
For more information, see RFC 5 and #12898
* transmute_copy - This function was moved to `mem`, with clarification that is
is not an error to invoke it with T/U that are different
sizes, but rather that it is strongly discouraged. This
function is now #[stable]
* forget - This function was moved to `mem` and marked #[stable]
* bump_box_refcount - This function was removed due to the deprecation of
managed boxes as well as its questionable utility.
* transmute_mut - This function was previously deprecated, and removed as part
of this commit.
* transmute_mut_unsafe - This function doesn't serve much of a purpose when it
can be achieved with an `as` in safe code, so it was
removed.
* transmute_lifetime - This function was removed because it is likely a strong
indication that code is incorrect in the first place.
* transmute_mut_lifetime - This function was removed for the same reasons as
`transmute_lifetime`
* copy_lifetime - This function was moved to `mem`, but it is marked
`#[unstable]` now due to the likelihood of being removed in
the future if it is found to not be very useful.
* copy_mut_lifetime - This function was also moved to `mem`, but had the same
treatment as `copy_lifetime`.
* copy_lifetime_vec - This function was removed because it is not used today,
and its existence is not necessary with DST
(copy_lifetime will suffice).
In summary, the cast module was stripped down to these functions, and then the
functions were moved to the `mem` module.
transmute - #[unstable]
transmute_copy - #[stable]
forget - #[stable]
copy_lifetime - #[unstable]
copy_mut_lifetime - #[unstable]
[breaking-change]
Few places where previous version of tidy script cannot find XXX:
* inside one-line comment preceding by a few spaces;
* inside multiline comments (now it finds it if multiline comment starts
on the same line with XXX).
Change occurences of XXX found by new tidy script.
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.
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.
It turns out that libuv was returning ENOSPC to us in our usage of the
uv_ipX_name functions. It also turns out that there may be an off-by-one in
libuv. For now just add one to the buffer size and handle the return value
correctly.
Closes#10663
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.
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
