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author | Colin Cross <ccross@android.com> | 2017-11-07 13:34:26 -0800 |
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committer | Colin Cross <ccross@android.com> | 2017-11-07 13:36:44 -0800 |
commit | 99c6dfaecc2e0a2452a4142b533035aa52dbe6f2 (patch) | |
tree | a73fd39996767719dffbedb455a02c6baafe417c /android/onceper.go | |
parent | 5c9cf6eb84f3130b09f19e030ef95239d3cb7527 (diff) | |
download | build_soong-99c6dfaecc2e0a2452a4142b533035aa52dbe6f2.tar.gz build_soong-99c6dfaecc2e0a2452a4142b533035aa52dbe6f2.tar.bz2 build_soong-99c6dfaecc2e0a2452a4142b533035aa52dbe6f2.zip |
Add OncePer.Get()
Allow functions to get the result associated with a OncePer key without
also specifiying a function. Panics if the key has not already been
set. Also replace the open-coded concurrent map implementation with
the new sync.Map.
Test: m checkbuild
Change-Id: I814fdb1ffffaee8398dc877af146e29638c8a6a8
Diffstat (limited to 'android/onceper.go')
-rw-r--r-- | android/onceper.go | 33 |
1 files changed, 16 insertions, 17 deletions
diff --git a/android/onceper.go b/android/onceper.go index 5f7a3102..f19f75c0 100644 --- a/android/onceper.go +++ b/android/onceper.go @@ -15,12 +15,12 @@ package android import ( + "fmt" "sync" - "sync/atomic" ) type OncePer struct { - values atomic.Value + values sync.Map valuesLock sync.Mutex } @@ -29,33 +29,32 @@ type valueMap map[interface{}]interface{} // Once computes a value the first time it is called with a given key per OncePer, and returns the // value without recomputing when called with the same key. key must be hashable. func (once *OncePer) Once(key interface{}, value func() interface{}) interface{} { - // Atomically load the map without locking. If this is the first call Load() will return nil - // and the type assertion will fail, leaving a nil map in m, but that's OK since m is only used - // for reads. - m, _ := once.values.Load().(valueMap) - if v, ok := m[key]; ok { + // Fast path: check if the key is already in the map + if v, ok := once.values.Load(key); ok { return v } + // Slow path: lock so that we don't call the value function twice concurrently once.valuesLock.Lock() defer once.valuesLock.Unlock() // Check again with the lock held - m, _ = once.values.Load().(valueMap) - if v, ok := m[key]; ok { + if v, ok := once.values.Load(key); ok { return v } - // Copy the existing map - newMap := make(valueMap, len(m)) - for k, v := range m { - newMap[k] = v - } - + // Still not in the map, call the value function and store it v := value() + once.values.Store(key, v) + + return v +} - newMap[key] = v - once.values.Store(newMap) +func (once *OncePer) Get(key interface{}) interface{} { + v, ok := once.values.Load(key) + if !ok { + panic(fmt.Errorf("Get() called before Once()")) + } return v } |