* Fix for: DefaultRwLock accumulates write-waiters, eventually fails to write lock #13163
* Comment out debug.print at the end of the last test.
* Code formatting
* - use equality test after lock/unlock rather than peeking into internals.
however, this is still implementation specific and only done for
DefaultRwLock.
- add num_reads maximum to ensure that reader threads stop if writer threads are
starved
- use relaxed orderings for the read atomic counter
- don't check at the end for non-zero read ops, since the reader threads may
only run once if they are starved
* More review changes
- Monotonic is sufficient for incrementing the reads counter
We already have a LICENSE file that covers the Zig Standard Library. We
no longer need to remind everyone that the license is MIT in every single
file.
Previously this was introduced to clarify the situation for a fork of
Zig that made Zig's LICENSE file harder to find, and replaced it with
their own license that required annual payments to their company.
However that fork now appears to be dead. So there is no need to
reinforce the copyright notice in every single file.
The primary purpose of this change is to eliminate one usage of
`usingnamespace` in the standard library - specifically the usage for
errno values in `std.os.linux`.
This is accomplished by truncating the `E` prefix from error values, and
making errno a proper enum.
A similar strategy can be used to eliminate some other `usingnamespace`
sites in the std lib.
* move concurrency primitives that always operate on kernel threads to
the std.Thread namespace
* remove std.SpinLock. Nobody should use this in a non-freestanding
environment; the other primitives are always preferable. In
freestanding, it will be necessary to put custom spin logic in there,
so there are no use cases for a std lib version.
* move some std lib files to the top level fields convention
* add std.Thread.spinLoopHint
* add std.Thread.Condition
* add std.Thread.Semaphore
* new implementation of std.Thread.Mutex for Windows and non-pthreads Linux
* add std.Thread.RwLock
Implementations provided by @kprotty
