mirror of https://github.com/golang/go.git
13f6be2833
In faketime mode, checkdead is responsible for jumping time forward to the next timer expiration, and waking an M to handle the newly ready timer. Currently it pulls the exact P that owns the next timer off of the pidle list. In theory this is efficient because that P is immediately eligible to run the timer without stealing. Unfortunately it is also fraught with peril because we are skipping all of the bookkeeping in pidleget: * Skipped updates to timerpMask mean that our timers may not be eligible for stealing, as they should be. * Skipped updates to idlepMask mean that our runq may not be eligible for stealing, as they should be. * Skipped updates to sched.npidle may break tracking of spinning Ms, potentially resulting in lost work. * Finally, as of CL 410122, skipped updates to p.limiterEvent may affect the GC limiter, or cause a fatal throw when another event occurs. The last case has finally undercovered this issue since it quickly results in a hard crash. We could add all of these updates into checkdead, but it is much more maintainable to keep this logic in one place and use pidleget here like everywhere else in the runtime. This means we probably won't wake the P owning the timer, meaning that the P will need to steal the timer, which is less efficient, but faketime is not a performance-sensitive build mode. Note that the M will automatically make itself a spinning M to make it eligible to steal since it is the only one running. Fixes #53294 For #52890 Change-Id: I4acc3d259b9b4d7dc02608581c8b4fd259f272e9 Reviewed-on: https://go-review.googlesource.com/c/go/+/411119 Run-TryBot: Michael Pratt <mpratt@google.com> Auto-Submit: Michael Pratt <mpratt@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com> |
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README.vendor
Vendoring in std and cmd
========================
The Go command maintains copies of external packages needed by the
standard library in the src/vendor and src/cmd/vendor directories.
In GOPATH mode, imports of vendored packages are resolved to these
directories following normal vendor directory logic
(see golang.org/s/go15vendor).
In module mode, std and cmd are modules (defined in src/go.mod and
src/cmd/go.mod). When a package outside std or cmd is imported
by a package inside std or cmd, the import path is interpreted
as if it had a "vendor/" prefix. For example, within "crypto/tls",
an import of "golang.org/x/crypto/cryptobyte" resolves to
"vendor/golang.org/x/crypto/cryptobyte". When a package with the
same path is imported from a package outside std or cmd, it will
be resolved normally. Consequently, a binary may be built with two
copies of a package at different versions if the package is
imported normally and vendored by the standard library.
Vendored packages are internally renamed with a "vendor/" prefix
to preserve the invariant that all packages have distinct paths.
This is necessary to avoid compiler and linker conflicts. Adding
a "vendor/" prefix also maintains the invariant that standard
library packages begin with a dotless path element.
The module requirements of std and cmd do not influence version
selection in other modules. They are only considered when running
module commands like 'go get' and 'go mod vendor' from a directory
in GOROOT/src.
Maintaining vendor directories
==============================
Before updating vendor directories, ensure that module mode is enabled.
Make sure GO111MODULE=off is not set ('on' or 'auto' should work).
Requirements may be added, updated, and removed with 'go get'.
The vendor directory may be updated with 'go mod vendor'.
A typical sequence might be:
cd src
go get -d golang.org/x/net@latest
go mod tidy
go mod vendor
Use caution when passing '-u' to 'go get'. The '-u' flag updates
modules providing all transitively imported packages, not only
the module providing the target package.
Note that 'go mod vendor' only copies packages that are transitively
imported by packages in the current module. If a new package is needed,
it should be imported before running 'go mod vendor'.