package context

Import Path
	context (on golang.org and go.dev)

Dependency Relation
	imports 5 packages, and imported by 12 packages

Involved Source Files
	d-> context.go

Exported Type Names

type CancelFunc (func) A CancelFunc tells an operation to abandon its work. A CancelFunc does not wait for the work to stop. A CancelFunc may be called by multiple goroutines simultaneously. After the first call, subsequent calls to a CancelFunc do nothing. func WithCancel(parent Context) (ctx Context, cancel CancelFunc) func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc)
type Context (interface) A Context carries a deadline, a cancellation signal, and other values across API boundaries. Context's methods may be called by multiple goroutines simultaneously. Deadline returns the time when work done on behalf of this context should be canceled. Deadline returns ok==false when no deadline is set. Successive calls to Deadline return the same results. Done returns a channel that's closed when work done on behalf of this context should be canceled. Done may return nil if this context can never be canceled. Successive calls to Done return the same value. The close of the Done channel may happen asynchronously, after the cancel function returns. WithCancel arranges for Done to be closed when cancel is called; WithDeadline arranges for Done to be closed when the deadline expires; WithTimeout arranges for Done to be closed when the timeout elapses. Done is provided for use in select statements: // Stream generates values with DoSomething and sends them to out // until DoSomething returns an error or ctx.Done is closed. func Stream(ctx context.Context, out chan<- Value) error { for { v, err := DoSomething(ctx) if err != nil { return err } select { case <-ctx.Done(): return ctx.Err() case out <- v: } } } See https://blog.golang.org/pipelines for more examples of how to use a Done channel for cancellation. If Done is not yet closed, Err returns nil. If Done is closed, Err returns a non-nil error explaining why: Canceled if the context was canceled or DeadlineExceeded if the context's deadline passed. After Err returns a non-nil error, successive calls to Err return the same error. Value returns the value associated with this context for key, or nil if no value is associated with key. Successive calls to Value with the same key returns the same result. Use context values only for request-scoped data that transits processes and API boundaries, not for passing optional parameters to functions. A key identifies a specific value in a Context. Functions that wish to store values in Context typically allocate a key in a global variable then use that key as the argument to context.WithValue and Context.Value. A key can be any type that supports equality; packages should define keys as an unexported type to avoid collisions. Packages that define a Context key should provide type-safe accessors for the values stored using that key: // Package user defines a User type that's stored in Contexts. package user import "context" // User is the type of value stored in the Contexts. type User struct {...} // key is an unexported type for keys defined in this package. // This prevents collisions with keys defined in other packages. type key int // userKey is the key for user.User values in Contexts. It is // unexported; clients use user.NewContext and user.FromContext // instead of using this key directly. var userKey key // NewContext returns a new Context that carries value u. func NewContext(ctx context.Context, u *User) context.Context { return context.WithValue(ctx, userKey, u) } // FromContext returns the User value stored in ctx, if any. func FromContext(ctx context.Context) (*User, bool) { u, ok := ctx.Value(userKey).(*User) return u, ok } func Background() Context func TODO() Context func WithCancel(parent Context) (ctx Context, cancel CancelFunc) func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) func WithValue(parent Context, key, val interface{}) Context func net/http.(*Request).Context() Context func net/http/httptrace.WithClientTrace(ctx Context, trace *httptrace.ClientTrace) Context func runtime/pprof.WithLabels(ctx Context, labels pprof.LabelSet) Context func runtime/trace.NewTask(pctx Context, taskType string) (ctx Context, task *trace.Task) func WithCancel(parent Context) (ctx Context, cancel CancelFunc) func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) func WithValue(parent Context, key, val interface{}) Context func crypto/tls.(*Dialer).DialContext(ctx Context, network, addr string) (net.Conn, error) func database/sql.(*Conn).BeginTx(ctx Context, opts *sql.TxOptions) (*sql.Tx, error) func database/sql.(*Conn).ExecContext(ctx Context, query string, args ...interface{}) (sql.Result, error) func database/sql.(*Conn).PingContext(ctx Context) error func database/sql.(*Conn).PrepareContext(ctx Context, query string) (*sql.Stmt, error) func database/sql.(*Conn).QueryContext(ctx Context, query string, args ...interface{}) (*sql.Rows, error) func database/sql.(*Conn).QueryRowContext(ctx Context, query string, args ...interface{}) *sql.Row func database/sql.(*DB).BeginTx(ctx Context, opts *sql.TxOptions) (*sql.Tx, error) func database/sql.(*DB).Conn(ctx Context) (*sql.Conn, error) func database/sql.(*DB).ExecContext(ctx Context, query string, args ...interface{}) (sql.Result, error) func database/sql.(*DB).PingContext(ctx Context) error func database/sql.(*DB).PrepareContext(ctx Context, query string) (*sql.Stmt, error) func database/sql.(*DB).QueryContext(ctx Context, query string, args ...interface{}) (*sql.Rows, error) func database/sql.(*DB).QueryRowContext(ctx Context, query string, args ...interface{}) *sql.Row func database/sql.(*Stmt).ExecContext(ctx Context, args ...interface{}) (sql.Result, error) func database/sql.(*Stmt).QueryContext(ctx Context, args ...interface{}) (*sql.Rows, error) func database/sql.(*Stmt).QueryRowContext(ctx Context, args ...interface{}) *sql.Row func database/sql.(*Tx).ExecContext(ctx Context, query string, args ...interface{}) (sql.Result, error) func database/sql.(*Tx).PrepareContext(ctx Context, query string) (*sql.Stmt, error) func database/sql.(*Tx).QueryContext(ctx Context, query string, args ...interface{}) (*sql.Rows, error) func database/sql.(*Tx).QueryRowContext(ctx Context, query string, args ...interface{}) *sql.Row func database/sql.(*Tx).StmtContext(ctx Context, stmt *sql.Stmt) *sql.Stmt func database/sql/driver.ConnBeginTx.BeginTx(ctx Context, opts driver.TxOptions) (driver.Tx, error) func database/sql/driver.Connector.Connect(Context) (driver.Conn, error) func database/sql/driver.ConnPrepareContext.PrepareContext(ctx Context, query string) (driver.Stmt, error) func database/sql/driver.ExecerContext.ExecContext(ctx Context, query string, args []driver.NamedValue) (driver.Result, error) func database/sql/driver.Pinger.Ping(ctx Context) error func database/sql/driver.QueryerContext.QueryContext(ctx Context, query string, args []driver.NamedValue) (driver.Rows, error) func database/sql/driver.SessionResetter.ResetSession(ctx Context) error func database/sql/driver.StmtExecContext.ExecContext(ctx Context, args []driver.NamedValue) (driver.Result, error) func database/sql/driver.StmtQueryContext.QueryContext(ctx Context, args []driver.NamedValue) (driver.Rows, error) func net.(*Dialer).DialContext(ctx Context, network, address string) (net.Conn, error) func net.(*ListenConfig).Listen(ctx Context, network, address string) (net.Listener, error) func net.(*ListenConfig).ListenPacket(ctx Context, network, address string) (net.PacketConn, error) func net.(*Resolver).LookupAddr(ctx Context, addr string) (names []string, err error) func net.(*Resolver).LookupCNAME(ctx Context, host string) (cname string, err error) func net.(*Resolver).LookupHost(ctx Context, host string) (addrs []string, err error) func net.(*Resolver).LookupIP(ctx Context, network, host string) ([]net.IP, error) func net.(*Resolver).LookupIPAddr(ctx Context, host string) ([]net.IPAddr, error) func net.(*Resolver).LookupMX(ctx Context, name string) ([]*net.MX, error) func net.(*Resolver).LookupNS(ctx Context, name string) ([]*net.NS, error) func net.(*Resolver).LookupPort(ctx Context, network, service string) (port int, err error) func net.(*Resolver).LookupSRV(ctx Context, service, proto, name string) (cname string, addrs []*net.SRV, err error) func net.(*Resolver).LookupTXT(ctx Context, name string) ([]string, error) func net/http.NewRequestWithContext(ctx Context, method, url string, body io.Reader) (*http.Request, error) func net/http.(*Request).Clone(ctx Context) *http.Request func net/http.(*Request).WithContext(ctx Context) *http.Request func net/http.(*Server).Shutdown(ctx Context) error func net/http/httptrace.ContextClientTrace(ctx Context) *httptrace.ClientTrace func net/http/httptrace.WithClientTrace(ctx Context, trace *httptrace.ClientTrace) Context func os/exec.CommandContext(ctx Context, name string, arg ...string) *exec.Cmd func runtime/pprof.Do(ctx Context, labels pprof.LabelSet, f func(Context)) func runtime/pprof.ForLabels(ctx Context, f func(key, value string) bool) func runtime/pprof.Label(ctx Context, key string) (string, bool) func runtime/pprof.SetGoroutineLabels(ctx Context) func runtime/pprof.WithLabels(ctx Context, labels pprof.LabelSet) Context func runtime/trace.Log(ctx Context, category, message string) func runtime/trace.Logf(ctx Context, category, format string, args ...interface{}) func runtime/trace.NewTask(pctx Context, taskType string) (ctx Context, task *trace.Task) func runtime/trace.StartRegion(ctx Context, regionType string) *trace.Region func runtime/trace.WithRegion(ctx Context, regionType string, fn func())
Exported Values
func Background() Context Background returns a non-nil, empty Context. It is never canceled, has no values, and has no deadline. It is typically used by the main function, initialization, and tests, and as the top-level Context for incoming requests.
var Canceled error Canceled is the error returned by Context.Err when the context is canceled.
var DeadlineExceeded error DeadlineExceeded is the error returned by Context.Err when the context's deadline passes.
func TODO() Context TODO returns a non-nil, empty Context. Code should use context.TODO when it's unclear which Context to use or it is not yet available (because the surrounding function has not yet been extended to accept a Context parameter).
func WithCancel(parent Context) (ctx Context, cancel CancelFunc) WithCancel returns a copy of parent with a new Done channel. The returned context's Done channel is closed when the returned cancel function is called or when the parent context's Done channel is closed, whichever happens first. Canceling this context releases resources associated with it, so code should call cancel as soon as the operations running in this Context complete.
func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) WithDeadline returns a copy of the parent context with the deadline adjusted to be no later than d. If the parent's deadline is already earlier than d, WithDeadline(parent, d) is semantically equivalent to parent. The returned context's Done channel is closed when the deadline expires, when the returned cancel function is called, or when the parent context's Done channel is closed, whichever happens first. Canceling this context releases resources associated with it, so code should call cancel as soon as the operations running in this Context complete.
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)). Canceling this context releases resources associated with it, so code should call cancel as soon as the operations running in this Context complete: func slowOperationWithTimeout(ctx context.Context) (Result, error) { ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond) defer cancel() // releases resources if slowOperation completes before timeout elapses return slowOperation(ctx) }
func WithValue(parent Context, key, val interface{}) Context WithValue returns a copy of parent in which the value associated with key is val. Use context Values only for request-scoped data that transits processes and APIs, not for passing optional parameters to functions. The provided key must be comparable and should not be of type string or any other built-in type to avoid collisions between packages using context. Users of WithValue should define their own types for keys. To avoid allocating when assigning to an interface{}, context keys often have concrete type struct{}. Alternatively, exported context key variables' static type should be a pointer or interface.