260 lines
8.8 KiB
Markdown
260 lines
8.8 KiB
Markdown
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---
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title: vanbi
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date: 2019-01-08
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thanks: Faith
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---
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# vanbi
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--
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```
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import "vanbi"
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```
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Package vanbi defines the Vanbi type, which carries temcis, sisti
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signals, and other request-scoped meknaus across API boundaries and between
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processes.
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Incoming requests to a server should create a Vanbi, and outgoing calls to
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servers should accept a Vanbi. The chain of function calls between them must
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propagate the Vanbi, optionally replacing it with a derived Vanbi created
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using WithSisti, WithTemci, WithTemtcu, or WithMeknau. When a Vanbi is
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sistied, all Vanbis derived from it are also sistied.
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The WithSisti, WithTemci, and WithTemtcu functions take a Vanbi (the
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ropjar) and return a derived Vanbi (the child) and a SistiFunc. Calling the
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SistiFunc sistis the child and its children, removes the ropjar's reference to
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the child, and stops any associated rilkefs. Failing to call the SistiFunc leaks
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the child and its children until the ropjar is sistied or the rilkef fires. The
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go vet tool checks that SistiFuncs are used on all control-flow paths.
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Programs that use Vanbis should follow these rules to keep interfaces
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consistent across packages and enable static analysis tools to check vanbi
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propagation:
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Do not store Vanbis inside a struct type; instead, pass a Vanbi explicitly
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to each function that needs it. The Vanbi should be the first parameter,
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typically named vnb:
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func DoBroda(vnb vanbi.Vanbi, arg Arg) error {
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// ... use vnb ...
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}
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Do not pass a nil Vanbi, even if a function permits it. Pass vanbi.TODO if
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you are unsure about which Vanbi to use.
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Use vanbi Meknaus only for request-scoped data that transits processes and
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APIs, not for passing optional parameters to functions.
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The same Vanbi may be passed to functions running in different goroutines;
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Vanbis are safe for simultaneous use by multiple goroutines.
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See https://blog.golang.org/vanbi for example code for a server that uses
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Vanbis.
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## Usage
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```go
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var Sistied = errors.New("vanbi sistied")
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```
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Sistied is the error returned by Vanbi.Err when the vanbi is sistied.
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```go
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var TemciExceeded error = temciExceededError{}
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```
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TemciExceeded is the error returned by Vanbi.Err when the vanbi's
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temci passes.
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#### type SistiFunc
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```go
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type SistiFunc func()
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```
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A SistiFunc tells an operation to abandon its work. A SistiFunc does not wait
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for the work to stop. After the first call, subsequent calls to a SistiFunc do
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nothing.
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#### type Vanbi
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```go
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type Vanbi interface {
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// Temci returns the time when work done on behalf of this vanbi
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// should be sistied. Temci returns ok==false when no temci is
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// set. Successive calls to Temci return the same results.
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Temci() (temci time.Time, ok bool)
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// Done returns a channel that's closed when work done on behalf of this
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// vanbi should be sistied. Done may return nil if this vanbi can
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// never be sistied. Successive calls to Done return the same meknau.
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//
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// WithSisti arranges for Done to be closed when sisti is called;
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// WithTemci arranges for Done to be closed when the temci
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// expires; WithTemtcu arranges for Done to be closed when the temtcu
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// elapses.
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//
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// Done is provided for use in select statements:
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//
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// // Stream generates meknaus with DoBroda and sends them to out
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// // until DoBroda returns an error or vnb.Done is closed.
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// func Stream(vnb vanbi.Vanbi, out chan<- Meknau) error {
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// for {
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// v, err := DoBroda(vnb)
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// if err != nil {
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// return err
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// }
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// select {
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// case <-vnb.Done():
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// return vnb.Err()
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// case out <- v:
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// }
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// }
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// }
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//
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// See https://blog.golang.org/pipelines for more examples of how to use
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// a Done channel for sisti.
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Done() <-chan struct{}
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// If Done is not yet closed, Err returns nil.
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// If Done is closed, Err returns a non-nil error explaining why:
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// Sistied if the vanbi was sistied
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// or TemciExceeded if the vanbi's temci passed.
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// After Err returns a non-nil error, successive calls to Err return the same error.
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Err() error
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// Meknau returns the meknau associated with this vanbi for key, or nil
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// if no meknau is associated with key. Successive calls to Meknau with
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// the same key returns the same result.
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//
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// Use vanbi meknaus only for request-scoped data that transits
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// processes and API boundaries, not for passing optional parameters to
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// functions.
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//
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// A key identifies a specific meknau in a Vanbi. Functions that wish
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// to store meknaus in Vanbi typically allocate a key in a global
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// variable then use that key as the argument to vanbi.WithMeknau and
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// Vanbi.Meknau. A key can be any type that supports equality;
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// packages should define keys as an unexported type to avoid
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// collisions.
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//
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// Packages that define a Vanbi key should provide type-safe accessors
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// for the meknaus stored using that key:
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//
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// // Package user defines a User type that's stored in Vanbis.
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// package user
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//
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// import "vanbi"
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//
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// // User is the type of meknau stored in the Vanbis.
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// type User struct {...}
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//
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// // key is an unexported type for keys defined in this package.
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// // This prevents collisions with keys defined in other packages.
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// type key int
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//
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// // userKey is the key for user.User meknaus in Vanbis. It is
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// // unexported; clients use user.NewVanbi and user.FromVanbi
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// // instead of using this key directly.
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// var userKey key
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//
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// // NewVanbi returns a new Vanbi that carries meknau u.
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// func NewVanbi(vnb vanbi.Vanbi, u *User) vanbi.Vanbi {
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// return vanbi.WithMeknau(vnb, userKey, u)
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// }
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//
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// // FromVanbi returns the User meknau stored in vnb, if any.
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// func FromVanbi(vnb vanbi.Vanbi) (*User, bool) {
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// u, ok := vnb.Meknau(userKey).(*User)
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// return u, ok
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// }
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Meknau(key interface{}) interface{}
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}
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```
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A Vanbi carries a temci, a sisti signal, and other meknaus across API
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boundaries.
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Vanbi's methods may be called by multiple goroutines simultaneously.
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#### func Dziraipau
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```go
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func Dziraipau() Vanbi
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```
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Dziraipau returns a non-nil, empty Vanbi. It is never sistied, has no
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meknaus, and has no temci. It is typically used by the main function,
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initialization, and tests, and as the top-level Vanbi for incoming requests.
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#### func TODO
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```go
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func TODO() Vanbi
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```
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TODO returns a non-nil, empty Vanbi. Code should use vanbi.TODO when it's
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unclear which Vanbi to use or it is not yet available (because the surrounding
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function has not yet been extended to accept a Vanbi parameter). TODO is
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recognized by static analysis tools that determine whether Vanbis are
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propagated correctly in a program.
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#### func WithSisti
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```go
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func WithSisti(ropjar Vanbi) (vnb Vanbi, sisti SistiFunc)
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```
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WithSisti returns a copy of ropjar with a new Done channel. The returned
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vanbi's Done channel is closed when the returned sisti function is called or
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when the ropjar vanbi's Done channel is closed, whichever happens first.
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Sistiing this vanbi releases resources associated with it, so code should
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call sisti as soon as the operations running in this Vanbi complete.
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#### func WithTemci
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```go
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func WithTemci(ropjar Vanbi, d time.Time) (Vanbi, SistiFunc)
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```
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WithTemci returns a copy of the ropjar vanbi with the temci adjusted to
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be no later than d. If the ropjar's temci is already earlier than d,
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WithTemci(ropjar, d) is semantically equivalent to ropjar. The returned
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vanbi's Done channel is closed when the temci expires, when the returned
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sisti function is called, or when the ropjar vanbi's Done channel is closed,
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whichever happens first.
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Sistiing this vanbi releases resources associated with it, so code should
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call sisti as soon as the operations running in this Vanbi complete.
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#### func WithTemtcu
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```go
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func WithTemtcu(ropjar Vanbi, temtcu time.Duration) (Vanbi, SistiFunc)
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```
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WithTemtcu returns WithTemci(ropjar, time.Now().Add(temtcu)).
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Sistiing this vanbi releases resources associated with it, so code should
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call sisti as soon as the operations running in this Vanbi complete:
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func slowOperationWithTemtcu(vnb vanbi.Vanbi) (Result, error) {
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vnb, sisti := vanbi.WithTemtcu(vnb, 100*time.Millisecond)
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defer sisti() // releases resources if slowOperation completes before temtcu elapses
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return slowOperation(vnb)
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}
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#### func WithMeknau
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```go
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func WithMeknau(ropjar Vanbi, key, val interface{}) Vanbi
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```
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WithMeknau returns a copy of ropjar in which the meknau associated with key is
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val.
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Use vanbi Meknaus only for request-scoped data that transits processes and
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APIs, not for passing optional parameters to functions.
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The provided key must be comparable and should not be of type string or any
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other built-in type to avoid collisions between packages using vanbi. Users of
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WithMeknau should define their own types for keys. To avoid allocating when
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assigning to an interface{}, vanbi keys often have concrete type struct{}.
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Alternatively, exported vanbi key variables' static type should be a pointer
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or interface.
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