This commit shows a proof-of-concept direction for std.Io.VTable to go,
which is to have general support for batching, timeouts, and
non-blocking.
I'm not sure if this is a good idea or not so I'm putting it up for
scrutiny.
This commit introduces `std.Io.operate`, `std.Io.Operation`, and
implements it experimentally for `FileReadStreaming`.
In `std.Io.Threaded`, the implementation is based on poll().
This commit shows how it can be used in `std.process.run` to collect
both stdout and stderr in a single-threaded program using
`std.Threaded.Io`.
It also demonstrates how to upgrade code that was previously using
`std.Io.poll` (*not* integrated with the interface!) using concurrency.
This may not be ideal since it makes the build runner no longer support
single-threaded mode. There is still a needed abstraction for
conveniently reading multiple File streams concurrently without
io.concurrent, but this commit demonstrates that such an API can be
built on top of the new `std.Io.operate` functionality.
In Zig standard library, Dir means an open directory handle. path
represents a file system identifier string. This function is better
named after "current path" than "current dir". "get" and "working" are
superfluous.
If the library isn't actually installed, `generated_bin` will be null,
causing this to panic about a missing dependency for itself; checking
for this state avoids this.
The previous logic was made really messy by the fact that upon entry to
the step eval worker, the step may not be ready to run, we may be racing
with other workers doing the same check, and we had already acquired our
RSS requirement even though we might not run. It also required iterating
all dependencies each time we were called to check whether we were even
ready to run yet.
A much better strategy is for each step to have an atomic counter
representing how many of its dependencies are yet to complete. When a
step completes (successfully or otherwise), it decrements this value for
all of its dependants, and if it drops any to 0, it schedules that step
to run. This means each step is scheduled exactly once, and only when
all of its dependencies have finished, reducing redundant checks and
hence contention. If the step being scheduled needs to claim RSS which
isn't available, then it is instead added to `memory_blocked_steps`,
which is iterated by the step worker after a step with an RSS claim
finishes.
This logic is more concise than before, simpler to understand, generally
more efficient, and fixes a bug in the RSS tracking. Also, as a nice
side effect, it should also play a little bit nicer with `Io.Threaded`'s
scheduling strategy, because we no longer spawn extremely short-lived
tasks all the time as we previously did.
Resolves: https://codeberg.org/ziglang/zig/issues/30742
Remove the RemoveDir step with no replacement. This step had no valid
purpose. Mutating source files? That should be done with
UpdateSourceFiles step. Deleting temporary directories? That required
creating the tmp directories in the configure phase which is broken.
Deleting cached artifacts? That's going to cause problems.
Similarly, remove the `Build.makeTempPath` function. This was used to
create a temporary path in the configure place which, again, is the
wrong place to do it.
Instead, the WriteFile step has been updated with more functionality:
tmp mode: In this mode, the directory will be placed inside "tmp" rather
than "o", and caching will be skipped. During the `make` phase, the step
will always do all the file system operations, and on successful build
completion, the dir will be deleted along with all other tmp
directories. The directory is therefore eligible to be used for
mutations by other steps. `Build.addTempFiles` is introduced to
initialize a WriteFile step with this mode.
mutate mode: The operations will not be performed against a freshly
created directory, but instead act against a temporary directory.
`Build.addMutateFiles` is introduced to initialize a WriteFile step with
this mode.
`Build.tmpPath` is introduced, which is a shortcut for
`Build.addTempFiles` followed by `WriteFile.getDirectory`.
* give Cache a gpa rather than arena because that's what it asks for
this gets the build runner compiling again on linux
this work is incomplete; it only moves code around so that environment
variables can be wrangled properly. a future commit will need to audit
the cancelation and error handling of this moved logic.
This commit includes some API changes which I agreed with Andrew as a
follow-up to the recent `Io.Group` changes:
* `Io.Group.await` *does* propagate cancelation to group tasks; it then
waits for them to complete, and *also* returns `error.Canceled`. The
assertion that group tasks handle `error.Canceled` "correctly" means
this behavior is loosely analagous to how awaiting a future works. The
important thing is that the semantics of `Group.await` and
`Future.await` are similar, and `error.Canceled` will always be
visible to the caller (assuming correct API usage).
* `Io.Group.awaitUncancelable` is removed.
* `Future.await` calls `recancel` only if the "child" task (the future
being awaited) did not acknowledge cancelation. If it did, then it is
assumed that the future will propagate `error.Canceled` through
`await` as needed.
Rename `wait` to `await` to be consistent with Future API. The
convention here is that this set of functionality goes together:
* async/concurrent
* await/cancel
Also rename Select `wait` to `await` for the same reason.
`Group.await` now can return `error.Canceled`. Furthermore,
`Group.await` does not auto-propagate cancelation. Instead, users should
follow the pattern of `defer group.cancel(io);` after initialization,
and doing `try group.await(io);` at the end of the success path.
Advanced logic can choose to do something other than this pattern in the
event of cancelation.
Additionally, fixes a bug in `std.Io.Threaded` future await, in which it
swallowed an `error.Canceled`. Now if a task is canceled while awaiting
a future, after propagating the cancel request, it also recancels,
meaning that the awaiting task will properly detect its own cancelation
at the next cancelation point.
Furthermore, fixes a bug in the compiler where `error.Canceled` was
being swallowed in `dispatchPrelinkWork`.
Finally, fixes std.crypto code that inappropriately used
`catch unreachable` in response to cancelation without even so much as a
comment explaining why it was believed to be unreachable. Now, those
functions have `error.Canceled` in the error set and propagate
cancelation properly.
With this way of doing things, `Group.await` has a nice property: even if
all tasks in the group are CPU bound and without cancelation points, the
`Group.await` can still be canceled. In such case, the task that was
waiting for `await` wakes up with a chance to do some more resource
cleanup tasks, such as canceling more things, before entering the
deferred `Group.cancel` call at which point it has to suspend until the
canceled but uninterruptible CPU bound tasks complete.
closes#30601
use the application's Io implementation where possible. This correctly
makes writing to stderr cancelable, fallible, and participate in the
application's event loop. It also removes one more hard-coded
dependency on a secondary Io implementation.
Andrew Kelley