compressio: stop worker-pool reference / dependency loop.

PiperOrigin-RevId: 212732300
Change-Id: I9a0b9b7c28e7b7439d34656dd4f2f6114d173e22

pkg/compressio/compressio.go

@@ -127,9 +127,9 @@ type result struct {
 // The goroutine will exit when input is closed, and the goroutine will close
 // output.
 type worker struct {
-	pool   *pool
-	input  chan *chunk
-	output chan result
+	hashPool *hashPool
+	input    chan *chunk
+	output   chan result
 }
 
 // work is the main work routine; see worker.
@@ -139,8 +139,8 @@ func (w *worker) work(compress bool, level int) {
 	var h hash.Hash
 
 	for c := range w.input {
-		if h == nil && w.pool.key != nil {
-			h = w.pool.getHash()
+		if h == nil && w.hashPool != nil {
+			h = w.hashPool.getHash()
 		}
 		if compress {
 			mw := io.Writer(c.compressed)
@@ -201,6 +201,42 @@ func (w *worker) work(compress bool, level int) {
 	}
 }
 
+type hashPool struct {
+	// mu protexts the hash list.
+	mu sync.Mutex
+
+	// key is the key used to create hash objects.
+	key []byte
+
+	// hashes is the hash object free list. Note that this cannot be
+	// globally shared across readers or writers, as it is key-specific.
+	hashes []hash.Hash
+}
+
+// getHash gets a hash object for the pool. It should only be called when the
+// pool key is non-nil.
+func (p *hashPool) getHash() hash.Hash {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if len(p.hashes) == 0 {
+		return hmac.New(sha256.New, p.key)
+	}
+
+	h := p.hashes[len(p.hashes)-1]
+	p.hashes = p.hashes[:len(p.hashes)-1]
+	return h
+}
+
+func (p *hashPool) putHash(h hash.Hash) {
+	h.Reset()
+
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	p.hashes = append(p.hashes, h)
+}
+
 // pool is common functionality for reader/writers.
 type pool struct {
 	// workers are the compression/decompression workers.
@@ -210,16 +246,6 @@ type pool struct {
 	// stream and is shared across both the reader and writer.
 	chunkSize uint32
 
-	// key is the key used to create hash objects.
-	key []byte
-
-	// hashMu protexts the hash list.
-	hashMu sync.Mutex
-
-	// hashes is the hash object free list. Note that this cannot be
-	// globally shared across readers or writers, as it is key-specific.
-	hashes []hash.Hash
-
 	// mu protects below; it is generally the responsibility of users to
 	// acquire this mutex before calling any methods on the pool.
 	mu sync.Mutex
@@ -236,19 +262,26 @@ type pool struct {
 
 	// lasSum records the hash of the last chunk processed.
 	lastSum []byte
+
+	// hashPool is the hash object pool. It cannot be embedded into pool
+	// itself as worker refers to it and that would stop pool from being
+	// GCed.
+	hashPool *hashPool
 }
 
 // init initializes the worker pool.
 //
 // This should only be called once.
 func (p *pool) init(key []byte, workers int, compress bool, level int) {
-	p.key = key
+	if key != nil {
+		p.hashPool = &hashPool{key: key}
+	}
 	p.workers = make([]worker, workers)
 	for i := 0; i < len(p.workers); i++ {
 		p.workers[i] = worker{
-			pool:   p,
-			input:  make(chan *chunk, 1),
-			output: make(chan result, 1),
+			hashPool: p.hashPool,
+			input:    make(chan *chunk, 1),
+			output:   make(chan result, 1),
 		}
 		go p.workers[i].work(compress, level) // S/R-SAFE: In save path only.
 	}
@@ -261,30 +294,7 @@ func (p *pool) stop() {
 		close(p.workers[i].input)
 	}
 	p.workers = nil
-}
-
-// getHash gets a hash object for the pool. It should only be called when the
-// pool key is non-nil.
-func (p *pool) getHash() hash.Hash {
-	p.hashMu.Lock()
-	defer p.hashMu.Unlock()
-
-	if len(p.hashes) == 0 {
-		return hmac.New(sha256.New, p.key)
-	}
-
-	h := p.hashes[len(p.hashes)-1]
-	p.hashes = p.hashes[:len(p.hashes)-1]
-	return h
-}
-
-func (p *pool) putHash(h hash.Hash) {
-	h.Reset()
-
-	p.hashMu.Lock()
-	defer p.hashMu.Unlock()
-
-	p.hashes = append(p.hashes, h)
+	p.hashPool = nil
 }
 
 // handleResult calls the callback.
@@ -361,11 +371,11 @@ func NewReader(in io.Reader, key []byte) (io.Reader, error) {
 		return nil, err
 	}
 
-	if r.key != nil {
-		h := r.getHash()
+	if r.hashPool != nil {
+		h := r.hashPool.getHash()
 		binary.WriteUint32(h, binary.BigEndian, r.chunkSize)
 		r.lastSum = h.Sum(nil)
-		r.putHash(h)
+		r.hashPool.putHash(h)
 		sum := make([]byte, len(r.lastSum))
 		if _, err := io.ReadFull(r.in, sum); err != nil {
 			return nil, err
@@ -477,7 +487,7 @@ func (r *reader) Read(p []byte) (int, error) {
 		}
 
 		var sum []byte
-		if r.key != nil {
+		if r.hashPool != nil {
 			sum = make([]byte, len(r.lastSum))
 			if _, err := io.ReadFull(r.in, sum); err != nil {
 				if err == io.EOF {
@@ -573,11 +583,11 @@ func NewWriter(out io.Writer, key []byte, chunkSize uint32, level int) (io.Write
 		return nil, err
 	}
 
-	if w.key != nil {
-		h := w.getHash()
+	if w.hashPool != nil {
+		h := w.hashPool.getHash()
 		binary.WriteUint32(h, binary.BigEndian, chunkSize)
 		w.lastSum = h.Sum(nil)
-		w.putHash(h)
+		w.hashPool.putHash(h)
 		if _, err := io.CopyN(w.out, bytes.NewReader(w.lastSum), int64(len(w.lastSum))); err != nil {
 			return nil, err
 		}
@@ -600,10 +610,10 @@ func (w *writer) flush(c *chunk) error {
 		return err
 	}
 
-	if w.key != nil {
+	if w.hashPool != nil {
 		io.CopyN(c.h, bytes.NewReader(w.lastSum), int64(len(w.lastSum)))
 		sum := c.h.Sum(nil)
-		w.putHash(c.h)
+		w.hashPool.putHash(c.h)
 		c.h = nil
 		if _, err := io.CopyN(w.out, bytes.NewReader(sum), int64(len(sum))); err != nil {
 			return err