ae3bb4a537
Currently fixalloc does not zero memory it reuses. This is dangerous with the hybrid barrier if the type may contain heap pointers, since it may cause us to observe a dead heap pointer on reuse. It's also error-prone since it's the only allocator that doesn't zero on allocation (mallocgc of course zeroes, but so do persistentalloc and sysAlloc). It's also largely pointless: for mcache, the caller immediately memclrs the allocation; and the two specials types are tiny so there's no real cost to zeroing them. Change fixalloc to zero allocations by default. The only type we don't zero by default is mspan. This actually requires that the spsn's sweepgen survive across freeing and reallocating a span. If we were to zero it, the following race would be possible: 1. The current sweepgen is 2. Span s is on the unswept list. 2. Direct sweeping sweeps span s, finds it's all free, and releases s to the fixalloc. 3. Thread 1 allocates s from fixalloc. Suppose this zeros s, including s.sweepgen. 4. Thread 1 calls s.init, which sets s.state to _MSpanDead. 5. On thread 2, background sweeping comes across span s in allspans and cas's s.sweepgen from 0 (sg-2) to 1 (sg-1). Now it thinks it owns it for sweeping. 6. Thread 1 continues initializing s. Everything breaks. I would like to fix this because it's obviously confusing, but it's a subtle enough problem that I'm leaving it alone for now. The solution may be to skip sweepgen 0, but then we have to think about wrap-around much more carefully. Updates #17503. Change-Id: Ie08691feed3abbb06a31381b94beb0a2e36a0613 Reviewed-on: https://go-review.googlesource.com/31368 Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org> |
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README.md
The Go Programming Language
Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.
For documentation about how to install and use Go, visit https://golang.org/ or load doc/install-source.html in your web browser.
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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 file). 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-source.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 https://golang.org/doc/install or doc/install.html for more details.