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https://github.com/seaweedfs/seaweedfs.git
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Chris Lu
ec83a87d68
defer guarantees the hasher returns to the pool even if h.Write or h.Sum panic, preventing pool leak under unexpected failure modes.
34 lines
987 B
Go
34 lines
987 B
Go
package s3lifecycle
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import (
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"crypto/sha256"
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"hash"
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"sync"
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)
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// ShardCount partitions the (bucket, key) keyspace for the per-shard
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// lifecycle reader. Workers receive one READ task per owned shard;
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// each shard's cursor advances independently.
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const ShardCount = 16
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// shardHashPool reuses sha256 hashers — ShardID is in the per-event hot
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// path and a fresh allocation per call shows up under load.
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var shardHashPool = sync.Pool{
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New: func() interface{} { return sha256.New() },
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}
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// ShardID maps (bucket, key) to a shard in [0, ShardCount). Stable across
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// restarts and across processes — identical (bucket, key) always lands on
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// the same shard. Implementation: top 4 bits of sha256(bucket || "/" || key).
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func ShardID(bucket, key string) int {
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h := shardHashPool.Get().(hash.Hash)
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defer shardHashPool.Put(h)
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h.Reset()
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h.Write([]byte(bucket))
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h.Write([]byte{'/'})
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h.Write([]byte(key))
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var buf [sha256.Size]byte
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sum := h.Sum(buf[:0])
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return int(sum[0] >> 4)
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}
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