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pkg/sql: use ring.Buffer in StmtBuf #41379

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merged 2 commits into from
Oct 10, 2019
Merged

pkg/sql: use ring.Buffer in StmtBuf #41379

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7f01be4
util/ring: clean up ring buffer package
nvanbenschoten Oct 7, 2019
42ec21d
pkg/sql: use ring.Buffer in StmtBuf
nvanbenschoten Oct 7, 2019
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19 changes: 10 additions & 9 deletions pkg/sql/conn_io.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ import (
"github.com/cockroachdb/cockroach/pkg/sql/sessiondata"
"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
"github.com/cockroachdb/cockroach/pkg/util/log"
"github.com/cockroachdb/cockroach/pkg/util/ring"
"github.com/cockroachdb/cockroach/pkg/util/syncutil"
"github.com/cockroachdb/errors"
"github.com/lib/pq/oid"
Expand Down Expand Up @@ -94,7 +95,7 @@ type StmtBuf struct {
cond *sync.Cond

// data contains the elements of the buffer.
data []Command
data ring.Buffer // []Command

// startPos indicates the index of the first command currently in data
// relative to the start of the connection.
Expand Down Expand Up @@ -398,7 +399,7 @@ func (buf *StmtBuf) Push(ctx context.Context, cmd Command) error {
if buf.mu.closed {
return errors.AssertionFailedf("buffer is closed")
}
buf.mu.data = append(buf.mu.data, cmd)
buf.mu.data.AddLast(cmd)
buf.mu.lastPos++

buf.mu.cond.Signal()
Expand Down Expand Up @@ -426,10 +427,11 @@ func (buf *StmtBuf) CurCmd() (Command, CmdPos, error) {
if err != nil {
return nil, 0, err
}
if cmdIdx < len(buf.mu.data) {
return buf.mu.data[cmdIdx], curPos, nil
len := buf.mu.data.Len()
if cmdIdx < len {
return buf.mu.data.Get(cmdIdx).(Command), curPos, nil
}
if cmdIdx != len(buf.mu.data) {
if cmdIdx != len {
return nil, 0, errors.AssertionFailedf(
"can only wait for next command; corrupt cursor: %d", errors.Safe(curPos))
}
Expand Down Expand Up @@ -473,8 +475,7 @@ func (buf *StmtBuf) ltrim(ctx context.Context, pos CmdPos) {
if buf.mu.startPos == pos {
break
}
buf.mu.data[0] = nil
buf.mu.data = buf.mu.data[1:]
buf.mu.data.RemoveFirst()
buf.mu.startPos++
}
}
Expand Down Expand Up @@ -509,7 +510,7 @@ func (buf *StmtBuf) seekToNextBatch() error {
buf.mu.Unlock()
return err
}
if cmdIdx == len(buf.mu.data) {
if cmdIdx == buf.mu.data.Len() {
buf.mu.Unlock()
return errors.AssertionFailedf("invalid seek start point")
}
Expand All @@ -529,7 +530,7 @@ func (buf *StmtBuf) seekToNextBatch() error {
return err
}

if _, ok := buf.mu.data[cmdIdx].(Sync); ok {
if _, ok := buf.mu.data.Get(cmdIdx).(Sync); ok {
foundSync = true
}

Expand Down
2 changes: 1 addition & 1 deletion pkg/sql/conn_io_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,7 @@ func TestStmtBufLtrim(t *testing.T) {
buf.AdvanceOne()
trimPos := CmdPos(2)
buf.ltrim(ctx, trimPos)
if l := len(buf.mu.data); l != 3 {
if l := buf.mu.data.Len(); l != 3 {
t.Fatalf("expected 3 left, got: %d", l)
}
if s := buf.mu.startPos; s != 2 {
Expand Down
147 changes: 76 additions & 71 deletions pkg/util/ring/ring_buffer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,22 +10,22 @@

package ring

const bufferInitialSize = 8

// Buffer is a deque maintained over a ring buffer. Note: it is backed by
// a slice (unlike container/ring one that is backed by a linked list).
// Buffer is a deque maintained over a ring buffer.
//
// Note: it is backed by a slice (unlike container/ring which is backed by a
// linked list).
type Buffer struct {
buffer []interface{}
head int // the index of the front of the deque.
tail int // the index of the first position right after the end of the deque.
head int // the index of the front of the buffer
tail int // the index of the first position after the end of the buffer

// indicates whether the deque is empty, necessary to distinguish
// between an empty deque and a deque that uses all of its capacity.
// Indicates whether the buffer is empty. Necessary to distinguish
// between an empty buffer and a buffer that uses all of its capacity.
nonEmpty bool
}

// Len returns the number of elements in the deque.
func (r Buffer) Len() int {
// Len returns the number of elements in the Buffer.
func (r *Buffer) Len() int {
if !r.nonEmpty {
return 0
}
Expand All @@ -38,83 +38,78 @@ func (r Buffer) Len() int {
}
}

// AddFirst add element to the front of the deque
// and doubles it's underlying slice if necessary.
func (r *Buffer) AddFirst(element interface{}) {
if cap(r.buffer) == 0 {
r.buffer = make([]interface{}, bufferInitialSize)
r.buffer[0] = element
r.tail = 1
} else {
if r.Len() == cap(r.buffer) {
newBuffer := make([]interface{}, 2*cap(r.buffer))
if r.head < r.tail {
copy(newBuffer[:r.Len()], r.buffer[r.head:r.tail])
} else {
copy(newBuffer[:cap(r.buffer)-r.head], r.buffer[r.head:])
copy(newBuffer[cap(r.buffer)-r.head:r.Len()], r.buffer[:r.tail])
}
r.head = 0
r.tail = cap(r.buffer)
r.buffer = newBuffer
}
r.head = (cap(r.buffer) + r.head - 1) % cap(r.buffer)
r.buffer[r.head] = element
}
r.nonEmpty = true
// Cap returns the capacity of the Buffer.
func (r *Buffer) Cap() int {
return cap(r.buffer)
}

// AddLast adds element to the end of the deque
// and doubles it's underlying slice if necessary.
func (r *Buffer) AddLast(element interface{}) {
if cap(r.buffer) == 0 {
r.buffer = make([]interface{}, bufferInitialSize)
r.buffer[0] = element
r.tail = 1
} else {
if r.Len() == cap(r.buffer) {
newBuffer := make([]interface{}, 2*cap(r.buffer))
if r.head < r.tail {
copy(newBuffer[:r.Len()], r.buffer[r.head:r.tail])
} else {
copy(newBuffer[:cap(r.buffer)-r.head], r.buffer[r.head:])
copy(newBuffer[cap(r.buffer)-r.head:r.Len()], r.buffer[:r.tail])
}
r.head = 0
r.tail = cap(r.buffer)
r.buffer = newBuffer
}
r.buffer[r.tail] = element
r.tail = (r.tail + 1) % cap(r.buffer)
}
r.nonEmpty = true
}

// Get returns an element at position pos in the deque (zero-based).
func (r Buffer) Get(pos int) interface{} {
// Get returns an element at position pos in the Buffer (zero-based).
func (r *Buffer) Get(pos int) interface{} {
if !r.nonEmpty || pos < 0 || pos >= r.Len() {
panic("unexpected behavior: index out of bounds")
panic("index out of bounds")
}
return r.buffer[(pos+r.head)%cap(r.buffer)]
}

// GetFirst returns an element at the front of the deque.
func (r Buffer) GetFirst() interface{} {
// GetFirst returns an element at the front of the Buffer.
func (r *Buffer) GetFirst() interface{} {
if !r.nonEmpty {
panic("unexpected behavior: getting first from empty deque")
panic("getting first from empty ring buffer")
}
return r.buffer[r.head]
}

// GetLast returns an element at the front of the deque.
func (r Buffer) GetLast() interface{} {
// GetLast returns an element at the front of the Buffer.
func (r *Buffer) GetLast() interface{} {
if !r.nonEmpty {
panic("unexpected behavior: getting last from empty deque")
panic("getting last from empty ring buffer")
}
return r.buffer[(cap(r.buffer)+r.tail-1)%cap(r.buffer)]
}

// RemoveFirst removes a single element from the front of the deque.
func (r *Buffer) grow(n int) {
newBuffer := make([]interface{}, n)
if r.head < r.tail {
copy(newBuffer[:r.Len()], r.buffer[r.head:r.tail])
} else {
copy(newBuffer[:cap(r.buffer)-r.head], r.buffer[r.head:])
copy(newBuffer[cap(r.buffer)-r.head:r.Len()], r.buffer[:r.tail])
}
r.head = 0
r.tail = cap(r.buffer)
r.buffer = newBuffer
}

func (r *Buffer) maybeGrow() {
if r.Len() != cap(r.buffer) {
return
}
n := 2 * cap(r.buffer)
if n == 0 {
n = 1
}
r.grow(n)
}

// AddFirst add element to the front of the Buffer and doubles it's underlying
// slice if necessary.
func (r *Buffer) AddFirst(element interface{}) {
r.maybeGrow()
r.head = (cap(r.buffer) + r.head - 1) % cap(r.buffer)
r.buffer[r.head] = element
r.nonEmpty = true
}

// AddLast adds element to the end of the Buffer and doubles it's underlying
// slice if necessary.
func (r *Buffer) AddLast(element interface{}) {
r.maybeGrow()
r.buffer[r.tail] = element
r.tail = (r.tail + 1) % cap(r.buffer)
r.nonEmpty = true
}

// RemoveFirst removes a single element from the front of the Buffer.
func (r *Buffer) RemoveFirst() {
if r.Len() == 0 {
panic("removing first from empty ring buffer")
Expand All @@ -126,7 +121,7 @@ func (r *Buffer) RemoveFirst() {
}
}

// RemoveLast removes a single element from the end of the deque.
// RemoveLast removes a single element from the end of the Buffer.
func (r *Buffer) RemoveLast() {
if r.Len() == 0 {
panic("removing last from empty ring buffer")
Expand All @@ -139,6 +134,16 @@ func (r *Buffer) RemoveLast() {
}
}

// Reserve reserves the provided number of elemnets in the Buffer. It is an
// error to reserve a size less than the Buffer's current length.
func (r *Buffer) Reserve(n int) {
if n < r.Len() {
panic("reserving fewer elements than current length")
} else if n > cap(r.buffer) {
r.grow(n)
}
}

// Reset makes Buffer treat its underlying memory as if it were empty. This
// allows for reusing the same memory again without explicitly removing old
// elements.
Expand Down
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