mirror of https://github.com/golang/go.git
d955dfb007
The previous implementation had several subtle issues. It's not
clear if any of these could actually be causing the flakiness
problems on openbsd/386, but fixing them should only help.
1. thrsleep() is implemented internally as unlock, then test *abort
(if abort != nil), then tsleep(). Under the current code, that makes
it theoretically possible that semasleep()/thrsleep() could release
waitsemalock, then a racing semawakeup() could acquire the lock,
increment waitsemacount, and call thrwakeup()/wakeup() before
thrsleep() reaches tsleep(). (In practice, OpenBSD's big kernel lock
seems unlikely to let this actually happen.)
The proper way to avoid this is to pass &waitsemacount as the abort
pointer to thrsleep so thrsleep knows to re-check it before going to
sleep, and to wakeup if it's non-zero. Then we avoid any races.
(I actually suspect openbsd's sema{sleep,wakeup}() could be further
simplified using cas/xadd instead of locks, but I don't want to be
more intrusive than necessary so late in the 1.4 release cycle.)
2. semasleep() takes a relative sleep duration, but thrsleep() needs
an absolute sleep deadline. Instead of recomputing the deadline each
iteration, compute it once up front and use (*Timespec)(nil) to signify
no deadline. Ensures we retry properly if there's a spurious wakeup.
3. Instead of assuming if thrsleep() woke up and waitsemacount wasn't
available that we must have hit the deadline, check that the system
call returned EWOULDBLOCK.
4. Instead of assuming that 64-bit systems are little-endian, compute
timediv() using a temporary int32 nsec and then assign it to tv_nsec.
LGTM=iant
R=jsing, iant
CC=golang-codereviews
https://golang.org/cl/137960043
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README
This is the source code repository for the Go programming language.
For documentation about how to install and use Go,
visit http://golang.org/ or load doc/install-source.html
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After installing Go, you can view a nicely formatted
doc/install-source.html by running godoc --http=:6060
and then visiting http://localhost:6060/doc/install/source.
Unless otherwise noted, the Go source files are distributed
under the BSD-style license found in the LICENSE file.
--
Binary Distribution Notes
If you have just untarred a binary Go distribution, you need to set
the environment variable $GOROOT to the full path of the go
directory (the one containing this README). You can omit the
variable if you unpack it into /usr/local/go, or if you rebuild
from sources by running all.bash (see doc/install.html).
You should also add the Go binary directory $GOROOT/bin
to your shell's path.
For example, if you extracted the tar file into $HOME/go, you might
put the following in your .profile:
export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin
See doc/install.html for more details.