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author | kevin.xu <cming.xu@gmail.com> | 2020-04-27 21:51:31 +0800 |
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committer | GitHub <noreply@github.com> | 2020-04-27 21:51:31 +0800 |
commit | e896ca54db67524afc20b644d43c72185e72dc0e (patch) | |
tree | 2a16f3a62a5cafd098f1f028c621f1b655589d69 /pkg/context/context.go | |
parent | 1f19624fa127d7d59cabe29593cc80b7fe6c81f8 (diff) | |
parent | 3c67754663f424f2ebbc0ff2a4c80e30618d5355 (diff) |
Merge pull request #1 from google/master
catch up
Diffstat (limited to 'pkg/context/context.go')
-rw-r--r-- | pkg/context/context.go | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/pkg/context/context.go b/pkg/context/context.go new file mode 100644 index 000000000..5319b6d8d --- /dev/null +++ b/pkg/context/context.go @@ -0,0 +1,137 @@ +// Copyright 2018 The gVisor Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +// Package context defines an internal context type. +// +// The given Context conforms to the standard Go context, but mandates +// additional methods that are specific to the kernel internals. Note however, +// that the Context described by this package carries additional constraints +// regarding concurrent access and retaining beyond the scope of a call. +// +// See the Context type for complete details. +package context + +import ( + "context" + "time" + + "gvisor.dev/gvisor/pkg/amutex" + "gvisor.dev/gvisor/pkg/log" +) + +type contextID int + +// Globally accessible values from a context. These keys are defined in the +// context package to resolve dependency cycles by not requiring the caller to +// import packages usually required to get these information. +const ( + // CtxThreadGroupID is the current thread group ID when a context represents + // a task context. The value is represented as an int32. + CtxThreadGroupID contextID = iota +) + +// ThreadGroupIDFromContext returns the current thread group ID when ctx +// represents a task context. +func ThreadGroupIDFromContext(ctx Context) (tgid int32, ok bool) { + if tgid := ctx.Value(CtxThreadGroupID); tgid != nil { + return tgid.(int32), true + } + return 0, false +} + +// A Context represents a thread of execution (hereafter "goroutine" to reflect +// Go idiosyncrasy). It carries state associated with the goroutine across API +// boundaries. +// +// While Context exists for essentially the same reasons as Go's standard +// context.Context, the standard type represents the state of an operation +// rather than that of a goroutine. This is a critical distinction: +// +// - Unlike context.Context, which "may be passed to functions running in +// different goroutines", it is *not safe* to use the same Context in multiple +// concurrent goroutines. +// +// - It is *not safe* to retain a Context passed to a function beyond the scope +// of that function call. +// +// In both cases, values extracted from the Context should be used instead. +type Context interface { + log.Logger + amutex.Sleeper + context.Context + + // UninterruptibleSleepStart indicates the beginning of an uninterruptible + // sleep state (equivalent to Linux's TASK_UNINTERRUPTIBLE). If deactivate + // is true and the Context represents a Task, the Task's AddressSpace is + // deactivated. + UninterruptibleSleepStart(deactivate bool) + + // UninterruptibleSleepFinish indicates the end of an uninterruptible sleep + // state that was begun by a previous call to UninterruptibleSleepStart. If + // activate is true and the Context represents a Task, the Task's + // AddressSpace is activated. Normally activate is the same value as the + // deactivate parameter passed to UninterruptibleSleepStart. + UninterruptibleSleepFinish(activate bool) +} + +// NoopSleeper is a noop implementation of amutex.Sleeper and UninterruptibleSleep +// methods for anonymous embedding in other types that do not implement sleeps. +type NoopSleeper struct { + amutex.NoopSleeper +} + +// UninterruptibleSleepStart does nothing. +func (NoopSleeper) UninterruptibleSleepStart(bool) {} + +// UninterruptibleSleepFinish does nothing. +func (NoopSleeper) UninterruptibleSleepFinish(bool) {} + +// Deadline returns zero values, meaning no deadline. +func (NoopSleeper) Deadline() (time.Time, bool) { + return time.Time{}, false +} + +// Done returns nil. +func (NoopSleeper) Done() <-chan struct{} { + return nil +} + +// Err returns nil. +func (NoopSleeper) Err() error { + return nil +} + +// logContext implements basic logging. +type logContext struct { + log.Logger + NoopSleeper +} + +// Value implements Context.Value. +func (logContext) Value(key interface{}) interface{} { + return nil +} + +// bgContext is the context returned by context.Background. +var bgContext = &logContext{Logger: log.Log()} + +// Background returns an empty context using the default logger. +// Generally, one should use the Task as their context when available, or avoid +// having to use a context in places where a Task is unavailable. +// +// Using a Background context for tests is fine, as long as no values are +// needed from the context in the tested code paths. +func Background() Context { + return bgContext +} |