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feat: chainstore: sharded mutex for filling chain height index
This PR introduces as sharded mutex within the ChainIndex#GetTipsetByHeight. It also replaces a go map with xsync.Map which doesn't require locking. The lock is taken when it appears that ChainIndex filling work should be started. After claiming the lock, the status of the cache is rechecked, if the entry is still missing, the fillCache is started. Thanks to @snissn and @arajasek for debugging and taking initial stabs at this. Supersedes #10866 and 10885 Signed-off-by: Jakub Sztandera <[email protected]>
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Jakub Sztandera
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May 19, 2023
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,75 @@ | ||
| package shardedmutex | ||
|
|
||
| import ( | ||
| "hash/maphash" | ||
| "sync" | ||
| ) | ||
|
|
||
| const cacheline = 64 | ||
|
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| // padding a mutex to a cacheline improves performance as the cachelines are not contested | ||
| // name old time/op new time/op delta | ||
| // Locks-8 74.6ns ± 7% 12.3ns ± 2% -83.54% (p=0.000 n=20+18) | ||
| type paddedMutex struct { | ||
| mt sync.Mutex | ||
| pad [cacheline - 8]uint8 | ||
| } | ||
|
|
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| type ShardedMutex struct { | ||
| shards []paddedMutex | ||
| } | ||
|
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| // New creates a new ShardedMutex with N shards | ||
| func New(n_shards int) ShardedMutex { | ||
| if n_shards < 1 { | ||
| panic("n_shards cannot be less than 1") | ||
| } | ||
| return ShardedMutex{ | ||
| shards: make([]paddedMutex, n_shards), | ||
| } | ||
| } | ||
|
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| func (sm ShardedMutex) Shards() int { | ||
| return len(sm.shards) | ||
| } | ||
|
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| func (sm ShardedMutex) Lock(shard int) { | ||
| sm.shards[shard].mt.Lock() | ||
| } | ||
|
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| func (sm ShardedMutex) Unlock(shard int) { | ||
| sm.shards[shard].mt.Unlock() | ||
| } | ||
|
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| func (sm ShardedMutex) GetLock(shard int) sync.Locker { | ||
| return &sm.shards[shard].mt | ||
| } | ||
|
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| type ShardedMutexFor[K any] struct { | ||
| inner ShardedMutex | ||
|
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| hasher func(maphash.Seed, K) uint64 | ||
| seed maphash.Seed | ||
| } | ||
|
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| func NewFor[K any](hasher func(maphash.Seed, K) uint64, n_shards int) ShardedMutexFor[K] { | ||
| return ShardedMutexFor[K]{ | ||
| inner: New(n_shards), | ||
| hasher: hasher, | ||
| seed: maphash.MakeSeed(), | ||
| } | ||
| } | ||
|
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| func (sm ShardedMutexFor[K]) shardFor(key K) int { | ||
| return int(sm.hasher(sm.seed, key) % uint64(len(sm.inner.shards))) | ||
| } | ||
|
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| func (sm ShardedMutexFor[K]) Lock(key K) { | ||
| sm.inner.Lock(sm.shardFor(key)) | ||
| } | ||
| func (sm ShardedMutexFor[K]) Unlock(key K) { | ||
| sm.inner.Unlock(sm.shardFor(key)) | ||
| } | ||
| func (sm ShardedMutexFor[K]) GetLock(key K) sync.Locker { | ||
| return sm.inner.GetLock(sm.shardFor(key)) | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,159 @@ | ||
| package shardedmutex | ||
|
|
||
| import ( | ||
| "fmt" | ||
| "hash/maphash" | ||
| "runtime" | ||
| "sync" | ||
| "sync/atomic" | ||
| "testing" | ||
| "time" | ||
| ) | ||
|
|
||
| func TestLockingDifferentShardsDoesNotBlock(t *testing.T) { | ||
| shards := 16 | ||
| sm := New(shards) | ||
| done := make(chan struct{}) | ||
| go func() { | ||
| select { | ||
| case <-done: | ||
| return | ||
| case <-time.After(5 * time.Second): | ||
| panic("test locked up") | ||
| } | ||
| }() | ||
| for i := 0; i < shards; i++ { | ||
| sm.Lock(i) | ||
| } | ||
|
|
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| close(done) | ||
| } | ||
| func TestLockingSameShardsBlocks(t *testing.T) { | ||
| shards := 16 | ||
| sm := New(shards) | ||
| wg := sync.WaitGroup{} | ||
| wg.Add(shards) | ||
| ch := make(chan int, shards) | ||
|
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| for i := 0; i < shards; i++ { | ||
| go func(i int) { | ||
| if i != 15 { | ||
| sm.Lock(i) | ||
| } | ||
| wg.Done() | ||
| wg.Wait() | ||
| sm.Lock((15 + i) % shards) | ||
| ch <- i | ||
| sm.Unlock(i) | ||
| }(i) | ||
| } | ||
|
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| wg.Wait() | ||
| for i := 0; i < 2*shards; i++ { | ||
| runtime.Gosched() | ||
| } | ||
| for i := 0; i < shards; i++ { | ||
| if a := <-ch; a != i { | ||
| t.Errorf("got %d instead of %d", a, i) | ||
| } | ||
| } | ||
| } | ||
|
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| func TestShardedByString(t *testing.T) { | ||
| shards := 16 | ||
| sm := NewFor(maphash.String, shards) | ||
|
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| wg1 := sync.WaitGroup{} | ||
| wg1.Add(shards * 20) | ||
| wg2 := sync.WaitGroup{} | ||
| wg2.Add(shards * 20) | ||
|
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| active := atomic.Int32{} | ||
| max := atomic.Int32{} | ||
|
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| for i := 0; i < shards*20; i++ { | ||
| go func(i int) { | ||
| wg1.Done() | ||
| wg1.Wait() | ||
| sm.Lock(fmt.Sprintf("goroutine %d", i)) | ||
| activeNew := active.Add(1) | ||
| for { | ||
| curMax := max.Load() | ||
| if curMax >= activeNew { | ||
| break | ||
| } | ||
| if max.CompareAndSwap(curMax, activeNew) { | ||
| break | ||
| } | ||
| } | ||
| for j := 0; j < 100; j++ { | ||
| runtime.Gosched() | ||
| } | ||
| active.Add(-1) | ||
| sm.Unlock(fmt.Sprintf("goroutine %d", i)) | ||
| wg2.Done() | ||
| }(i) | ||
| } | ||
|
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| wg2.Wait() | ||
|
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| if max.Load() != 16 { | ||
| t.Fatal("max load not achieved", max.Load()) | ||
| } | ||
|
|
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| } | ||
|
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| func BenchmarkShardedMutex(b *testing.B) { | ||
| shards := 16 | ||
| sm := New(shards) | ||
|
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| done := atomic.Int32{} | ||
| go func() { | ||
| for { | ||
| sm.Lock(0) | ||
| sm.Unlock(0) | ||
| if done.Load() != 0 { | ||
| return | ||
| } | ||
| } | ||
| }() | ||
| for i := 0; i < 100; i++ { | ||
| runtime.Gosched() | ||
| } | ||
|
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| b.ResetTimer() | ||
| for i := 0; i < b.N; i++ { | ||
| sm.Lock(1) | ||
| sm.Unlock(1) | ||
| } | ||
| done.Add(1) | ||
| } | ||
|
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| func BenchmarkShardedMutexOf(b *testing.B) { | ||
| shards := 16 | ||
| sm := NewFor(maphash.String, shards) | ||
|
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| str1 := "string1" | ||
| str2 := "string2" | ||
|
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| done := atomic.Int32{} | ||
| go func() { | ||
| for { | ||
| sm.Lock(str1) | ||
| sm.Unlock(str1) | ||
| if done.Load() != 0 { | ||
| return | ||
| } | ||
| } | ||
| }() | ||
| for i := 0; i < 100; i++ { | ||
| runtime.Gosched() | ||
| } | ||
|
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| b.ResetTimer() | ||
| for i := 0; i < b.N; i++ { | ||
| sm.Lock(str2) | ||
| sm.Unlock(str2) | ||
| } | ||
| done.Add(1) | ||
| } |