Add WithInversionCache and use pointer methods (#160)

There appears to be writes to value receivers.

Add `WithInversionCache(bool)` to disable cache.

Fixes #159

inversion_tree.go

@@ -14,7 +14,7 @@ import (
 // The tree uses a Reader-Writer mutex to make it thread-safe
 // when accessing cached matrices and inserting new ones.
 type inversionTree struct {
-	mutex *sync.RWMutex
+	mutex sync.RWMutex
 	root  inversionNode
 }
 
@@ -26,21 +26,22 @@ type inversionNode struct {
 // newInversionTree initializes a tree for storing inverted matrices.
 // Note that the root node is the identity matrix as it implies
 // there were no errors with the original data.
-func newInversionTree(dataShards, parityShards int) inversionTree {
+func newInversionTree(dataShards, parityShards int) *inversionTree {
 	identity, _ := identityMatrix(dataShards)
-	root := inversionNode{
-		matrix:   identity,
-		children: make([]*inversionNode, dataShards+parityShards),
-	}
-	return inversionTree{
-		mutex: &sync.RWMutex{},
-		root:  root,
+	return &inversionTree{
+		root: inversionNode{
+			matrix:   identity,
+			children: make([]*inversionNode, dataShards+parityShards),
+		},
 	}
 }
 
 // GetInvertedMatrix returns the cached inverted matrix or nil if it
 // is not found in the tree keyed on the indices of invalid rows.
-func (t inversionTree) GetInvertedMatrix(invalidIndices []int) matrix {
+func (t *inversionTree) GetInvertedMatrix(invalidIndices []int) matrix {
+	if t == nil {
+		return nil
+	}
 	// Lock the tree for reading before accessing the tree.
 	t.mutex.RLock()
 	defer t.mutex.RUnlock()
@@ -63,7 +64,10 @@ var errAlreadySet = errors.New("the root node identity matrix is already set")
 // keyed by the indices of invalid rows.  The total number of shards
 // is required for creating the proper length lists of child nodes for
 // each node.
-func (t inversionTree) InsertInvertedMatrix(invalidIndices []int, matrix matrix, shards int) error {
+func (t *inversionTree) InsertInvertedMatrix(invalidIndices []int, matrix matrix, shards int) error {
+	if t == nil {
+		return nil
+	}
 	// If no invalid indices were given then we are done because the
 	// root node is already set with the identity matrix.
 	if len(invalidIndices) == 0 {
@@ -86,7 +90,7 @@ func (t inversionTree) InsertInvertedMatrix(invalidIndices []int, matrix matrix,
 	return nil
 }
 
-func (n inversionNode) getInvertedMatrix(invalidIndices []int, parent int) matrix {
+func (n *inversionNode) getInvertedMatrix(invalidIndices []int, parent int) matrix {
 	// Get the child node to search next from the list of children.  The
 	// list of children starts relative to the parent index passed in
 	// because the indices of invalid rows is sorted (by default).  As we
@@ -117,7 +121,7 @@ func (n inversionNode) getInvertedMatrix(invalidIndices []int, parent int) matri
 	return node.matrix
 }
 
-func (n inversionNode) insertInvertedMatrix(invalidIndices []int, matrix matrix, shards, parent int) {
+func (n *inversionNode) insertInvertedMatrix(invalidIndices []int, matrix matrix, shards, parent int) {
 	// As above, get the child node to search next from the list of children.
 	// The list of children starts relative to the parent index passed in
 	// because the indices of invalid rows is sorted (by default).  As we

options.go

@@ -19,6 +19,7 @@ type options struct {
 	usePAR1Matrix                         bool
 	useCauchy                             bool
 	fastOneParity                         bool
+	inversionCache                        bool
 
 	// stream options
 	concReads  bool
@@ -27,9 +28,10 @@ type options struct {
 }
 
 var defaultOptions = options{
-	maxGoroutines: 384,
-	minSplitSize:  -1,
-	fastOneParity: false,
+	maxGoroutines:  384,
+	minSplitSize:   -1,
+	fastOneParity:  false,
+	inversionCache: true,
 
 	// Detect CPU capabilities.
 	useSSSE3:  cpuid.CPU.Supports(cpuid.SSSE3),
@@ -109,6 +111,15 @@ func WithConcurrentStreamWrites(enabled bool) Option {
 	}
 }
 
+// WithInversionCache allows to control the inversion cache.
+// This will cache reconstruction matrices so they can be reused.
+// Enabled by default.
+func WithInversionCache(enabled bool) Option {
+	return func(o *options) {
+		o.inversionCache = enabled
+	}
+}
+
 // WithStreamBlockSize allows to set a custom block size per round of reads/writes.
 // If not set, any shard size set with WithAutoGoroutines will be used.
 // If WithAutoGoroutines is also unset, 4MB will be used.

reedsolomon.go

@@ -110,7 +110,7 @@ type reedSolomon struct {
 	ParityShards int // Number of parity shards, should not be modified.
 	Shards       int // Total number of shards. Calculated, and should not be modified.
 	m            matrix
-	tree         inversionTree
+	tree         *inversionTree
 	parity       [][]byte
 	o            options
 	mPool        sync.Pool
@@ -333,7 +333,9 @@ func New(dataShards, parityShards int, opts ...Option) (Encoder, error) {
 	// The inversion root node will have the identity matrix as
 	// its inversion matrix because it implies there are no errors
 	// with the original data.
-	r.tree = newInversionTree(dataShards, parityShards)
+	if r.o.inversionCache {
+		r.tree = newInversionTree(dataShards, parityShards)
+	}
 
 	r.parity = make([][]byte, parityShards)
 	for i := range r.parity {

reedsolomon_test.go

@@ -142,6 +142,7 @@ func testOpts() [][]Option {
 		{WithMaxGoroutines(5000), WithMinSplitSize(500000), withSSSE3(false), withAVX2(false), withAVX512(false)},
 		{WithMaxGoroutines(1), WithMinSplitSize(500000), withSSSE3(false), withAVX2(false), withAVX512(false)},
 		{WithAutoGoroutines(50000), WithMinSplitSize(500)},
+		{WithInversionCache(false)},
 	}
 	for _, o := range opts[:] {
 		if defaultOptions.useSSSE3 {