go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/gae/filter/dscache/memcache.go (about)

     1  // Copyright 2020 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package dscache
    16  
    17  import (
    18  	"context"
    19  	"time"
    20  
    21  	"go.chromium.org/luci/common/errors"
    22  
    23  	"go.chromium.org/luci/gae/service/memcache"
    24  )
    25  
    26  // States for a memcache entry. itemFlagUnknown exists to distinguish the
    27  // default zero state from a valid state, but shouldn't ever be observed in
    28  // memcache.
    29  const (
    30  	itemFlagUnknown uint32 = iota
    31  	itemFlagHasData
    32  	itemFlagHasLock
    33  )
    34  
    35  type memcacheItem struct {
    36  	item memcache.Item
    37  }
    38  
    39  type memcacheImpl struct{}
    40  
    41  func (memcacheImpl) PutLocks(ctx context.Context, keys []string, timeout time.Duration) error {
    42  	if len(keys) == 0 {
    43  		return nil
    44  	}
    45  	items := make([]memcache.Item, len(keys))
    46  	for i, key := range keys {
    47  		items[i] = memcache.NewItem(ctx, key).
    48  			SetFlags(itemFlagHasLock).
    49  			SetExpiration(timeout)
    50  	}
    51  	return memcache.Set(ctx, items...)
    52  }
    53  
    54  func (memcacheImpl) DropLocks(ctx context.Context, keys []string) error {
    55  	if len(keys) == 0 {
    56  		return nil
    57  	}
    58  	return errors.Filter(memcache.Delete(ctx, keys...), memcache.ErrCacheMiss)
    59  }
    60  
    61  func (memcacheImpl) TryLockAndFetch(ctx context.Context, keys []string, nonce []byte, timeout time.Duration) ([]CacheItem, error) {
    62  	if len(keys) == 0 {
    63  		return nil, nil
    64  	}
    65  
    66  	mcItems := make([]memcache.Item, len(keys))
    67  	for i, key := range keys {
    68  		if key == "" {
    69  			continue
    70  		}
    71  		mcItems[i] = memcache.NewItem(ctx, key).
    72  			SetFlags(itemFlagHasLock).
    73  			SetExpiration(timeout).
    74  			SetValue(nonce)
    75  	}
    76  
    77  	if err := memcache.Add(ctx, mcItems...); err != nil {
    78  		// Ignore this error. Either we couldn't add them because they exist
    79  		// (so, not an issue), or because memcache is having sad times (in which
    80  		// case we'll see so in the Get which immediately follows this).
    81  	}
    82  
    83  	// We'll return this error as is in the end, along with all items that were
    84  	// fetched successfully.
    85  	err := errors.Filter(memcache.Get(ctx, mcItems...), memcache.ErrCacheMiss)
    86  
    87  	items := make([]CacheItem, len(mcItems))
    88  	for i, mcItem := range mcItems {
    89  		if mcItem == nil {
    90  			continue // cache miss or a gap in "keys"
    91  		}
    92  		if flag := mcItem.Flags(); flag == itemFlagUnknown || flag > itemFlagHasLock {
    93  			continue // unrecognized memcache entry, treat it as a cache miss
    94  		}
    95  		items[i] = memcacheItem{mcItem}
    96  	}
    97  
    98  	return items, err
    99  }
   100  
   101  func (memcacheImpl) CompareAndSwap(ctx context.Context, items []CacheItem) error {
   102  	if len(items) == 0 {
   103  		return nil
   104  	}
   105  	mcItems := make([]memcache.Item, len(items))
   106  	for i, item := range items {
   107  		mcItems[i] = item.(memcacheItem).item
   108  	}
   109  	return memcache.CompareAndSwap(ctx, mcItems...)
   110  }
   111  
   112  // Implement CacheItem interface for memcacheItem.
   113  
   114  func (m memcacheItem) Key() string {
   115  	return m.item.Key()
   116  }
   117  
   118  func (m memcacheItem) Nonce() []byte {
   119  	if m.item.Flags() == itemFlagHasLock {
   120  		return m.item.Value()
   121  	}
   122  	return nil
   123  }
   124  
   125  func (m memcacheItem) Data() []byte {
   126  	if m.item.Flags() == itemFlagHasData {
   127  		return m.item.Value()
   128  	}
   129  	return nil
   130  }
   131  
   132  func (m memcacheItem) Prefix() []byte {
   133  	return nil
   134  }
   135  
   136  func (m memcacheItem) PromoteToData(data []byte, exp time.Duration) {
   137  	if m.item.Flags() != itemFlagHasLock {
   138  		panic("only locks should be promoted")
   139  	}
   140  	m.item.SetFlags(itemFlagHasData)
   141  	m.item.SetExpiration(exp)
   142  	m.item.SetValue(data)
   143  }
   144  
   145  func (m memcacheItem) PromoteToIndefiniteLock() {
   146  	if m.item.Flags() != itemFlagHasLock {
   147  		panic("only locks should be promoted")
   148  	}
   149  	m.item.SetFlags(itemFlagHasLock)
   150  	m.item.SetExpiration(0)
   151  	m.item.SetValue(nil)
   152  }