Add asynq/x/rate package

- Added a directory /x for external, experimental packeges
- Added a `rate` package to enable rate limiting across multiple asynq worker servers

context.go

@@ -6,49 +6,16 @@ package asynq
 
 import (
 	"context"
-	"time"
 
-	"github.com/hibiken/asynq/internal/base"
+	asynqcontext "github.com/hibiken/asynq/internal/context"
 )
 
-// A taskMetadata holds task scoped data to put in context.
-type taskMetadata struct {
-	id         string
-	maxRetry   int
-	retryCount int
-	qname      string
-}
-
-// ctxKey type is unexported to prevent collisions with context keys defined in
-// other packages.
-type ctxKey int
-
-// metadataCtxKey is the context key for the task metadata.
-// Its value of zero is arbitrary.
-const metadataCtxKey ctxKey = 0
-
-// createContext returns a context and cancel function for a given task message.
-func createContext(msg *base.TaskMessage, deadline time.Time) (context.Context, context.CancelFunc) {
-	metadata := taskMetadata{
-		id:         msg.ID.String(),
-		maxRetry:   msg.Retry,
-		retryCount: msg.Retried,
-		qname:      msg.Queue,
-	}
-	ctx := context.WithValue(context.Background(), metadataCtxKey, metadata)
-	return context.WithDeadline(ctx, deadline)
-}
-
 // GetTaskID extracts a task ID from a context, if any.
 //
 // ID of a task is guaranteed to be unique.
 // ID of a task doesn't change if the task is being retried.
 func GetTaskID(ctx context.Context) (id string, ok bool) {
-	metadata, ok := ctx.Value(metadataCtxKey).(taskMetadata)
-	if !ok {
-		return "", false
-	}
-	return metadata.id, true
+	return asynqcontext.GetTaskID(ctx)
 }
 
 // GetRetryCount extracts retry count from a context, if any.
@@ -56,11 +23,7 @@ func GetTaskID(ctx context.Context) (id string, ok bool) {
 // Return value n indicates the number of times associated task has been
 // retried so far.
 func GetRetryCount(ctx context.Context) (n int, ok bool) {
-	metadata, ok := ctx.Value(metadataCtxKey).(taskMetadata)
-	if !ok {
-		return 0, false
-	}
-	return metadata.retryCount, true
+	return asynqcontext.GetRetryCount(ctx)
 }
 
 // GetMaxRetry extracts maximum retry from a context, if any.
@@ -68,20 +31,12 @@ func GetRetryCount(ctx context.Context) (n int, ok bool) {
 // Return value n indicates the maximum number of times the assoicated task
 // can be retried if ProcessTask returns a non-nil error.
 func GetMaxRetry(ctx context.Context) (n int, ok bool) {
-	metadata, ok := ctx.Value(metadataCtxKey).(taskMetadata)
-	if !ok {
-		return 0, false
-	}
-	return metadata.maxRetry, true
+	return asynqcontext.GetMaxRetry(ctx)
 }
 
 // GetQueueName extracts queue name from a context, if any.
 //
 // Return value qname indicates which queue the task was pulled from.
 func GetQueueName(ctx context.Context) (qname string, ok bool) {
-	metadata, ok := ctx.Value(metadataCtxKey).(taskMetadata)
-	if !ok {
-		return "", false
-	}
-	return metadata.qname, true
+	return asynqcontext.GetQueueName(ctx)
 }