With the old logic, it was possible for a bunch of processes to queue up
to update a cache entry, and then each to do so one at a time. Now, it
rechecks whether there still a cache miss or another process has
completed the work in the interim.
When checking a cache entry with no input files for a hit, if
`createFile` returned `error.WouldBlock` we would forget about the fact
that the file has been created, and all future checks will assume that a
cache hit has happened, even though one never has or does, leading to
rare `FileNotFound` errors trying the access the protected files.
This fix works by writing an extra byte to the manifest file to
distinguish hits and misses when there no input files to write.
* docs(std.math): elaborate on difference between absCast and absInt
* docs(std.rand.Random.weightedIndex): elaborate on likelihood
I think this makes it easier to understand.
* langref: add small reminder
* docs(std.fs.path.extension): brevity
* docs(std.bit_set.StaticBitSet): mention the specific types
* std.debug.TTY: explain what purpose this struct serves
This should also make it clearer that this struct is not supposed to provide unrelated terminal manipulation functionality such as setting the cursor position or something because terminals are complicated and we should keep this struct simple and focused on debugging.
* langref(package listing): brevity
* langref: explain what exactly `threadlocal` causes to happen
* std.array_list: link between swapRemove and orderedRemove
Maybe this can serve as a TLDR and make it easier to decide.
* PrefetchOptions.locality: clarify docs that this is a range
This confused me previously and I thought I can only use either 0 or 3.
* fix typos and more
* std.builtin.CallingConvention: document some CCs
* langref: explain possibly cryptic names
I think it helps knowing what exactly these acronyms (@clz and @ctz) and
abbreviations (@popCount) mean.
* variadic function error: add missing preposition
* std.fmt.format docs: nicely hyphenate
* help menu: say what to optimize for
I think this is slightly more specific than just calling it
"optimizations". These are speed optimizations. I used the word
"performance" here.
This fixes `.INVAL => unreachable` being triggered by the cache system
on macOS when multiple processes race to create the same compilation.
The problem is that when two processes race to create a file, it
sometimes returns ENOENT even though that error code is nonsensical for
this situation.
Commit 2b0929929d67e222ca6a9523a3a594ed456c4a51 purportedly solved this,
but it did not open the file with write permissions, leading to the
EINVAL panic later on. This commit remedies the situation by introducing
a loop and simply retrying when the ENOENT occurs.
There are no dir components, so you would think that this was
unreachable, however we have observed on macOS two processes racing
to do openat() with O_CREAT manifest in ENOENT.
Now that this API is used by the build system, these debug logs are
problematic because build scripts run in debug mode, making these logs
noisy output.
