Interface update, per-method Contexts.

service/memcache/interface.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package memcache
 
-// Interface is the full interface to the memcache service.
+import (
+        "github.com/luci/luci-go/common/errors"
+        "golang.org/x/net/context"
+)
+
+func filterItems(lme errors.LazyMultiError, items []Item, nilErr error) ([]Item, []int) {
+        idxMap := make([]int, 0, len(items))
+        retItems := make([]Item, 0, len(items))
+        for i, itm := range items {
+                if itm != nil {
+                        idxMap = append(idxMap, i)
+                        retItems = append(retItems, itm)
+                } else {
+                        lme.Assign(i, nilErr)
+                }
+        }
+        return retItems, idxMap
+}
+
+func multiCall(items []Item, nilErr error, inner func(items []Item, cb RawCB) error) error {
+        lme := errors.NewLazyMultiError(len(items))
+        realItems, idxMap := filterItems(lme, items, nilErr)
+        j := 0
+        err := inner(realItems, func(err error) {
+                lme.Assign(idxMap[j], err)
+                j++
+        })
+        if err == nil {
+                err = lme.Get()
+                if len(items) == 1 {
+                        err = errors.SingleError(err)
+                }
+        }
+        return err
+}
+
+// NewItem creates a new, mutable, memcache item.
+func NewItem(c context.Context, key string) Item {
+        return Raw(c).NewItem(key)
+}
+
+// Add writes items to memcache iff they don't already exist.
 //
-// The *Multi methods may return a "github.com/luci/luci-go/common/errors".MultiError
-// if the rpc to the server was successful, but, e.g. some of the items were
-// missing. They may also return a regular error, if, for example, the rpc
-// failed outright.
-type Interface interface {

[dnj, 2016/09/01 15:25:40]

Big change here is that I axed this Interface and collapsed the *Multi calls
into vararg calls.

-        // NewItem creates a new, mutable, memcache item.
-        NewItem(key string) Item
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func Add(c context.Context, items ...Item) error {
+        return multiCall(items, ErrNotStored, Raw(c).AddMulti)
+}
 
-        // Add puts a single item into memcache, but only if it didn't exist in
-        // memcache before.
-        Add(item Item) error
+// Set writes items into memcache unconditionally.
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func Set(c context.Context, items ...Item) error {
+        return multiCall(items, ErrNotStored, Raw(c).SetMulti)
+}
 
-        // Set the item in memcache, whether or not it exists.
-        Set(item Item) error
+func getMultiImpl(raw RawInterface, items []Item) error {
+        lme := errors.NewLazyMultiError(len(items))
+        realItems, idxMap := filterItems(lme, items, ErrCacheMiss)
+        if len(realItems) == 0 {
+                return lme.Get()
+        }
 
-        // Get retrieves an item from memcache.
-        //
-        // On a cache miss ErrCacheMiss will be returned. Item will always be
-        // returned, even on a miss, but it's value may be empty if it was a miss.
-        Get(key string) (Item, error)
+        keys := make([]string, len(realItems))
+        for i, itm := range realItems {
+                keys[i] = itm.Key()
+        }
 
-        // Delete removes an item from memcache.
-        Delete(key string) error
+        j := 0
+        err := raw.GetMulti(keys, func(item Item, err error) {
+                i := idxMap[j]
+                if !lme.Assign(i, err) {
+                        items[i].SetAll(item)
+                }
+                j++
+        })
+        if err == nil {
+                err = lme.Get()
+                if len(items) == 1 {

[dnj, 2016/09/01 15:25:40]

(This is the "single argument, single error" logic; you'll see this everywhere.)

+                        err = errors.SingleError(err)
+                }
+        }
+        return err
+}
 
-        // CompareAndSwap accepts an item which is the result of Get() or GetMulti().
-        // The Get functions add a secret field to item ('CasID'), which is used as
-        // the "compare" value for the "CompareAndSwap". The actual "Value" field of
-        // the object set by the Get functions is the "swap" value.
-        //
-        // Example:
-        //   mc := memcache.Get(context)
-        //   itm := mc.NewItem("aKey")
-        //   mc.Get(itm) // check error
-        //   itm.SetValue(append(itm.Value(), []byte("more bytes")))
-        //   mc.CompareAndSwap(itm) // check error
-        CompareAndSwap(item Item) error
+// Get retrieves items from memcache.
+func Get(c context.Context, items ...Item) error {
+        return getMultiImpl(Raw(c), items)
+}
 
-        // Batch operations; GetMulti takes a []Item instead of []string to improve
-        // ergonomics when streamlining these operations.
-        AddMulti(items []Item) error
-        SetMulti(items []Item) error
-        GetMulti(items []Item) error
-        DeleteMulti(keys []string) error
-        CompareAndSwapMulti(items []Item) error
+// GetKey is a convenience method for generating and retrieving an Item instance
+// for the specified from memcache key.
+//
+// On a cache miss ErrCacheMiss will be returned. Item will always be
+// returned, even on a miss, but it's value may be empty if it was a miss.
+func GetKey(c context.Context, key string) (Item, error) {
+        raw := Raw(c)
+        ret := raw.NewItem(key)
+        err := getMultiImpl(raw, []Item{ret})
+        return ret, err
+}
 
-        // Increment adds delta to the uint64 contained at key. If the memcache key
-        // is missing, it's populated with initialValue before applying delta (i.e.
-        // the final value would be initialValue+delta).
-        //
-        // Underflow caps at 0, overflow wraps back to 0.
-        //
-        // If key contains a value which is not exactly 8 bytes, it's assumed to
-        // contain non-number data and this method will return an error.
-        Increment(key string, delta int64, initialValue uint64) (newValue uint64, err error)
+// Delete deletes items from memcache.
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func Delete(c context.Context, keys ...string) error {
+        lme := errors.NewLazyMultiError(len(keys))
+        i := 0
+        err := Raw(c).DeleteMulti(keys, func(err error) {
+                lme.Assign(i, err)
+                i++
+        })
+        if err == nil {
+                err = lme.Get()
+                if len(keys) == 1 {
+                        err = errors.SingleError(err)
+                }
+        }
+        return err
+}
 
-        // IncrementExisting is like Increment, except that the valu must exist
-        // already.
-        IncrementExisting(key string, delta int64) (newValue uint64, err error)
+// CompareAndSwap writes the given item that was previously returned by Get, if
+// the value was neither modified or evicted between the Get and the
+// CompareAndSwap calls.
+//
+// Example:
+//   itm := memcache.NewItem(context, "aKey")
+//   memcache.Get(context, itm) // check error
+//   itm.SetValue(append(itm.Value(), []byte("more bytes")))
+//   memcache.CompareAndSwap(context, itm) // check error
+//
+// If only one item is provided its error will be returned directly. If more
+// than one item is provided, an errors.MultiError will be returned in the
+// event of an error, with a given error index corresponding to the error
+// encountered when processing the item at that index.
+func CompareAndSwap(c context.Context, items ...Item) error {
+        return multiCall(items, ErrNotStored, Raw(c).CompareAndSwapMulti)
+}
 
-        // Flush dumps the entire memcache state.
-        Flush() error
+// Increment adds delta to the uint64 contained at key. If the memcache key
+// is missing, it's populated with initialValue before applying delta (i.e.
+// the final value would be initialValue+delta).
+//
+// Underflow caps at 0, overflow wraps back to 0.
+//
+// If key contains a value which is not exactly 8 bytes, it's assumed to
+// contain non-number data and this method will return an error.
+func Increment(c context.Context, key string, delta int64, initialValue uint64) (uint64, error) {
+        return Raw(c).Increment(key, delta, &initialValue)
+}
 
-        // Stats gets some best-effort statistics about the current state of memcache.
-        Stats() (*Statistics, error)
+// IncrementExisting is like Increment, except that the valu must exist
+// already.
+func IncrementExisting(c context.Context, key string, delta int64) (uint64, error) {
+        return Raw(c).Increment(key, delta, nil)
+}
 
-        Raw() RawInterface
+// Flush dumps the entire memcache state.
+func Flush(c context.Context) error {
+        return Raw(c).Flush()
 }
+
+// Stats gets some best-effort statistics about the current state of memcache.
+func Stats(c context.Context) (*Statistics, error) {
+        return Raw(c).Stats()
+}