ctxext

package
Version: v0.3.7 Latest Latest
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Published: Aug 2, 2015 License: MIT Imports: 2 Imported by: 0

Documentation

Overview

Package ctxext provides multiple useful context constructors.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func WithDeadlineFraction

func WithDeadlineFraction(ctx context.Context, fraction float64) (
	context.Context, context.CancelFunc)

WithDeadlineFraction returns a Context with a fraction of the original context's timeout. This is useful in sequential pipelines of work, where one might try options and fall back to others depending on the time available, or failure to respond. For example:

// getPicture returns a picture from our encrypted database
// we have a pipeline of multiple steps. we need to:
// - get the data from a database
// - decrypt it
// - apply many transforms
//
// we **know** that each step takes increasingly more time.
// The transforms are much more expensive than decryption, and
// decryption is more expensive than the database lookup.
// If our database takes too long (i.e. >0.2 of available time),
// there's no use in continuing.
func getPicture(ctx context.Context, key string) ([]byte, error) {
  // fractional timeout contexts to the rescue!

  // try the database with 0.2 of remaining time.
  ctx1, _ := ctxext.WithDeadlineFraction(ctx, 0.2)
  val, err := db.Get(ctx1, key)
  if err != nil {
    return nil, err
  }

  // try decryption with 0.3 of remaining time.
  ctx2, _ := ctxext.WithDeadlineFraction(ctx, 0.3)
  if val, err = decryptor.Decrypt(ctx2, val); err != nil {
    return nil, err
  }

  // try transforms with all remaining time. hopefully it's enough!
  return transformer.Transform(ctx, val)
}

Types

This section is empty.

Source Files

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