Before this patch, the MN scheduler waits for the IO with the
following steps:
1. `poll(fd, timeout=0)` to check fd is ready or not.
2. if fd is not ready, waits with MN thread scheduler
3. call `func` to issue the blocking I/O call
The advantage of advanced `poll()` is we can wait for the
IO ready for any fds. However `poll()` becomes overhead
for already ready fds.
This patch changes the steps like:
1. call `func` to issue the blocking I/O call
2. if the `func` returns `EWOULDBLOCK` the fd is `O_NONBLOCK`
and we need to wait for fd is ready so that waits with MN
thread scheduler.
In this case, we can wait only for `O_NONBLOCK` fds. Otherwise
it waits with blocking operations such as `read()` system call.
However we don't need to call `poll()` to check fd is ready
in advance.
With this patch we can observe performance improvement
on microbenchmark which repeats blocking I/O (not
`O_NONBLOCK` fd) with and without MN thread scheduler.
```ruby
require 'benchmark'
f = open('/dev/null', 'w')
f.sync = true
TN = 1
N = 1_000_000 / TN
Benchmark.bm{|x|
x.report{
TN.times.map{
Thread.new{
N.times{f.print '.'}
}
}.each(&:join)
}
}
__END__
TN = 1
user system total real
ruby32 0.393966 0.101122 0.495088 ( 0.495235)
ruby33 0.493963 0.089521 0.583484 ( 0.584091)
ruby33+MN 0.639333 0.200843 0.840176 ( 0.840291) <- Slow
this+MN 0.512231 0.099091 0.611322 ( 0.611074) <- Good
```
This patch introduce M:N thread scheduler for Ractor system.
In general, M:N thread scheduler employs N native threads (OS threads)
to manage M user-level threads (Ruby threads in this case).
On the Ruby interpreter, 1 native thread is provided for 1 Ractor
and all Ruby threads are managed by the native thread.
From Ruby 1.9, the interpreter uses 1:1 thread scheduler which means
1 Ruby thread has 1 native thread. M:N scheduler change this strategy.
Because of compatibility issue (and stableness issue of the implementation)
main Ractor doesn't use M:N scheduler on default. On the other words,
threads on the main Ractor will be managed with 1:1 thread scheduler.
There are additional settings by environment variables:
`RUBY_MN_THREADS=1` enables M:N thread scheduler on the main ractor.
Note that non-main ractors use the M:N scheduler without this
configuration. With this configuration, single ractor applications
run threads on M:1 thread scheduler (green threads, user-level threads).
`RUBY_MAX_CPU=n` specifies maximum number of native threads for
M:N scheduler (default: 8).
This patch will be reverted soon if non-easy issues are found.
[Bug #19842]
Because a thread calling IO#close now blocks in a native condvar wait,
it's possible for there to be _no_ threads left to actually handle
incoming signals/ubf calls/etc.
This manifested as failing tests on Solaris 10 (SPARC), because:
* One thread called IO#close, which sent a SIGVTALRM to the other
thread to interrupt it, and then waited on the condvar to be notified
that the reading thread was done.
* One thread was calling IO#read, but it hadn't yet reached the actual
call to select(2) when the SIGVTALRM arrived, so it never unblocked
itself.
This results in a deadlock.
The fix is to use a real Ruby mutex for the close lock; that way, the
closing thread goes into sigwait-sleep and can keep trying to interrupt
the select(2) thread.
See the discussion in: https://github.com/ruby/ruby/pull/7865/
When one thread is closing a file descriptor whilst another thread is
concurrently reading it, we need to wait for the reading thread to be
done with it to prevent a potential EBADF (or, worse, file descriptor
reuse).
At the moment, that is done by keeping a list of threads still using the
file descriptor in io_close_fptr. It then continually calls
rb_thread_schedule() in fptr_finalize_flush until said list is empty.
That busy-looping seems to behave rather poorly on some OS's,
particulary FreeBSD. It can cause the TestIO#test_race_gets_and_close
test to fail (even with its very long 200 second timeout) because the
closing thread starves out the using thread.
To fix that, I introduce the concept of struct rb_io_close_wait_list; a
list of threads still using a file descriptor that we want to close. We
call `rb_notify_fd_close` to let the thread scheduler know we're closing
a FD, which fills the list with threads. Then, we call
rb_notify_fd_close_wait which will block the thread until all of the
still-using threads are done.
This is implemented with a condition variable sleep, so no busy-looping
is required.
[Bug #19415]
If multiple threads attemps to load the same file concurrently
it's not a circular dependency issue.
So we check that the existing ThreadShield is owner by the current
fiber before warning about circular dependencies.
[Bug #19415]
If multiple threads attemps to load the same file concurrently
it's not a circular dependency issue.
So we check that the existing ThreadShield is owner by the current
fiber before warning about circular dependencies.
According to MSVC manual (*1), cl.exe can skip including a header file
when that:
- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.
GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).
Sun C lacked #pragma once for a looong time. Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.
This changeset modifies header files so that each of them include
strictly one #ifndef...#endif. I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]
*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html
One day, I could not resist the way it was written. I finally started
to make the code clean. This changeset is the beginning of a series of
housekeeping commits. It is a simple refactoring; split internal.h into
files, so that we can divide and concur in the upcoming commits. No
lines of codes are either added or removed, except the obvious file
headers/footers. The generated binary is identical to the one before.
