Unfortunately, trying again until the cancellation request is
acknowledged has been observed to incur a large amount of overhead,
and usually strong cancellation guarantees are not needed, so the
race condition is not handled here. Users who want to avoid this
have this menu of options instead:
* Use no libc, in which case Zig std lib can avoid the race (tracking
issue: https://codeberg.org/ziglang/zig/issues/30049)
* Use musl libc
* Use `std.Io.Evented`. But this is not implemented yet. Tracked by
- https://codeberg.org/ziglang/zig/issues/30050
- https://codeberg.org/ziglang/zig/issues/30051
glibc + threaded is the only problematic combination.
On a heavily loaded Linux 6.17.5, I observed a maximum of 20 attempts
not acknowledged before the timeout (including exponential backoff) was
sufficient, despite the heavy load.
The time wasted here sleeping is mitigated by the fact that, later on,
the system will likely wait for the canceled task, causing it to
indefinitely yield until the canceled task finishes, and the task must
acknowledge the cancel before it proceeds to that point.
Now, before a syscall is entered, beginSyscall is called, which may
return error.Canceled. After syscall returns, whether error or success,
endSyscall is called. If the syscall returns EINTR then checkCancel is
called.
`cancelRequested` is removed from the std.Io VTable for now, with plans
to replace it with a more powerful API that allows protection against
cancellation requests.
closes#25751
while still preserving the guarantee about async() being assigned a unit
of concurrency (or immediately running the task), this change:
* retains the error from calling getCpuCount()
* spawns all threads in detached mode, using WaitGroup to join them
* treats all workers the same regardless of whether they are processing
concurrent or async tasks. one thread pool does all the work, while
respecting async and concurrent limits.
This is a reimplementation of Io.Threaded that fixes the issues
highlighted in the recent Zulip discussion. It's poorly tested but it
does successfully run to completion the litmust test example that I
offered in the discussion.
This implementation has the following key design decisions:
- `t.cpu_count` is used as the threadpool size.
- `t.concurrency_limit` is used as the maximum number of
"burst, one-shot" threads that can be spawned by `io.concurrent` past
`t.cpu_count`.
- `t.available_thread_count` is the number of threads in the pool that
is not currently busy with work (the bookkeeping happens in the worker
function).
- `t.one_shot_thread_count` is the number of active threads that were
spawned by `io.concurrent` past `t.cpu_count`.
In this implementation:
- `io.async` first tries to decrement `t.available_thread_count`. If
there are no threads available, it tries to spawn a new one if possible,
otherwise it runs the task immediately.
- `io.concurrent` first tries to use a thread in the pool same as
`io.async`, but on failure (no available threads and pool size limit
reached) it tries to spawn a new one-shot thread. One shot threads
run a different main function that just executes one task, decrements
the number of active one shot threads, and then exits.
A relevant future improvement is to have one-shot threads stay on for a
few seconds (and potentially pick up a new task) to amortize spawning
costs.
Previously, fs.path handled a few of the Windows path types, but not all of them, and only a few of them correctly/consistently. This commit aims to make `std.fs.path` correct and consistent in handling all possible Win32 path types.
This commit also slightly nudges the codebase towards a separation of Win32 paths and NT paths, as NT paths are not actually distinguishable from Win32 paths from looking at their contents alone (i.e. `\Device\Foo` could be an NT path or a Win32 rooted path, no way to tell without external context). This commit formalizes `std.fs.path` being fully concerned with Win32 paths, and having no special detection/handling of NT paths.
Resources on Windows path types, and Win32 vs NT paths:
- https://googleprojectzero.blogspot.com/2016/02/the-definitive-guide-on-win32-to-nt.html
- https://chrisdenton.github.io/omnipath/Overview.html
- https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file
API additions/changes/deprecations
- `std.os.windows.getWin32PathType` was added (it is analogous to `RtlDetermineDosPathNameType_U`), while `std.os.windows.getNamespacePrefix` and `std.os.windows.getUnprefixedPathType` were deleted. `getWin32PathType` forms the basis on which the updated `std.fs.path` functions operate.
- `std.fs.path.parsePath`, `std.fs.path.parsePathPosix`, and `std.fs.path.parsePathWindows` were added, while `std.fs.path.windowsParsePath` was deprecated. The new `parsePath` functions provide the "root" and the "kind" of a path, which is platform-specific. The now-deprecated `windowsParsePath` did not handle all possible path types, while the new `parsePathWindows` does.
- `std.fs.path.diskDesignator` has been deprecated in favor of `std.fs.path.parsePath`, and same deal with `diskDesignatorWindows` -> `parsePathWindows`
- `relativeWindows` is now a compile error when *not* targeting Windows, while `relativePosix` is now a compile error when targeting Windows. This is because those functions read/use the CWD path which will behave improperly when used from a system with different path semantics (e.g. calling `relativePosix` from a Windows system with a CWD like `C:\foo\bar` will give you a bogus result since that'd be treated as a single relative component when using POSIX semantics). This also allows `relativeWindows` to use Windows-specific APIs for getting the CWD and environment variables to cut down on allocations.
- `componentIterator`/`ComponentIterator.init` have been made infallible. These functions used to be able to error on UNC paths with an empty server component, and on paths that were assumed to be NT paths, but now:
+ We follow the lead of `RtlDetermineDosPathNameType_U`/`RtlGetFullPathName_U` in how it treats a UNC path with an empty server name (e.g. `\\\share`) and allow it, even if it'll be invalid at the time of usage
+ Now that `std.fs.path` assumes paths are Win32 paths and not NT paths, we don't have to worry about NT paths
Behavior changes
- `std.fs.path` generally: any combinations of mixed path separators for UNC paths are universally supported, e.g. `\/server/share`, `/\server\share`, `/\server/\\//share` are all seen as equivalent UNC paths
- `resolveWindows` handles all path types more appropriately/consistently.
+ `//` and `//foo` used to be treated as a relative path, but are now seen as UNC paths
+ If a rooted/drive-relative path cannot be resolved against anything more definite, the result will remain a rooted/drive-relative path.
+ I've created [a script to generate the results of a huge number of permutations of different path types](https://gist.github.com/squeek502/9eba7f19cad0d0d970ccafbc30f463bf) (the result of running the script is also included for anyone that'd like to vet the behavior).
- `dirnameWindows` now treats the drive-relative root as the dirname of a drive-relative path with a component, e.g. `dirname("C:foo")` is now `C:`, whereas before it would return null. `dirnameWindows` also handles local device paths appropriately now.
- `basenameWindows` now handles all path types more appropriately. The most notable change here is `//a` being treated as a partial UNC path now and therefore `basename` will return `""` for it, whereas before it would return `"a"`
- `relativeWindows` will now do its best to resolve against the most appropriate CWD for each path, e.g. relative for `D:foo` will look at the CWD to check if the drive letter matches, and if not, look at the special environment variable `=D:` to get the shell-defined CWD for that drive, and if that doesn't exist, then it'll resolve against `D:\`.
Implementation details
- `resolveWindows` previously looped through the paths twice to build up the relevant info before doing the actual resolution. Now, `resolveWindows` iterates backwards once and keeps track of which paths are actually relevant using a bit set, which also allows it to break from the loop when it's no longer possible for earlier paths to matter.
- A standalone test was added to test parts of `relativeWindows` since the CWD resolution logic depends on CWD information from the PEB and environment variables
Edge cases worth noting
- A strange piece of trivia that I found out while working on this is that it's technically possible to have a drive letter that it outside the intended A-Z range, or even outside the ASCII range entirely. Since we deal with both WTF-8 and WTF-16 paths, `path[0]`/`path[1]`/`path[2]` will not always refer to the same bits of information, so to get consistent behavior, some decision about how to deal with this edge case had to be made. I've made the choice to conform with how `RtlDetermineDosPathNameType_U` works, i.e. treat the first WTF-16 code unit as the drive letter. This means that when working with WTF-8, checking for drive-relative/drive-absolute paths is a bit more complicated. For more details, see the lengthy comment in `std.os.windows.getWin32PathType`
- `relativeWindows` will now almost always be able to return either a fully-qualified absolute path or a relative path, but there's one scenario where it may return a rooted path: when the CWD gotten from the PEB is not a drive-absolute or UNC path (if that's actually feasible/possible?). An alternative approach to this scenario might be to resolve against the `HOMEDRIVE` env var if available, and/or default to `C:\` as a last resort in order to guarantee the result of `relative` is never a rooted path.
- Partial UNC paths (e.g. `\\server` instead of `\\server\share`) are a bit awkward to handle, generally. Not entirely sure how best to handle them, so there may need to be another pass in the future to iron out any issues that arise. As of now the behavior is:
+ For `relative`, any part of a UNC disk designator is treated as the "root" and therefore isn't applicable for relative paths, e.g. calling `relative` with `\\server` and `\\server\share` will result in `\\server\share` rather than just `share` and if `relative` is called with `\\server\foo` and `\\server\bar` the result will be `\\server\bar` rather than `..\bar`
+ For `resolve`, any part of a UNC disk designator is also treated as the "root", but relative and rooted paths are still elligable for filling in missing portions of the disk designator, e.g. `resolve` with `\\server` and `foo` or `\foo` will result in `\\server\foo`
Fixes#25703Closes#25702
Apple's own headers and tbd files prefer to think of Mac Catalyst as a distinct
OS target. Earlier, when DriverKit support was added to LLVM, it was represented
a distinct OS. So why Apple decided to only represent Mac Catalyst as an ABI in
the target triple is beyond me. But this isn't the first time they've ignored
established target triple norms (see: armv7k and aarch64_32) and it probably
won't be the last.
While doing this, I also audited all Darwin OS prongs throughout the codebase
and made sure they cover all the tags.
This fixes package fetching on Windows.
Previously, `Async/GroupClosure` allocations were only aligned for the
closure struct type, which resulted in panics when `context_alignment`
(or `result_alignment` for that matter) had a greater alignment.
restores code closer to master branch in hopes of avoiding a regression
that was introduced when this was based on openSelfExe rather than
GetModuleFileNameExW.
