diff options
Diffstat (limited to 'vendor/github.com/go-sql-driver/mysql/buffer.go')
| -rw-r--r-- | vendor/github.com/go-sql-driver/mysql/buffer.go | 95 |
1 files changed, 65 insertions, 30 deletions
diff --git a/vendor/github.com/go-sql-driver/mysql/buffer.go b/vendor/github.com/go-sql-driver/mysql/buffer.go index eb4748bf44..0774c5c8c2 100644 --- a/vendor/github.com/go-sql-driver/mysql/buffer.go +++ b/vendor/github.com/go-sql-driver/mysql/buffer.go @@ -15,47 +15,69 @@ import ( ) const defaultBufSize = 4096 +const maxCachedBufSize = 256 * 1024 // A buffer which is used for both reading and writing. // This is possible since communication on each connection is synchronous. // In other words, we can't write and read simultaneously on the same connection. // The buffer is similar to bufio.Reader / Writer but zero-copy-ish // Also highly optimized for this particular use case. +// This buffer is backed by two byte slices in a double-buffering scheme type buffer struct { - buf []byte + buf []byte // buf is a byte buffer who's length and capacity are equal. nc net.Conn idx int length int timeout time.Duration + dbuf [2][]byte // dbuf is an array with the two byte slices that back this buffer + flipcnt uint // flipccnt is the current buffer counter for double-buffering } +// newBuffer allocates and returns a new buffer. func newBuffer(nc net.Conn) buffer { - var b [defaultBufSize]byte + fg := make([]byte, defaultBufSize) return buffer{ - buf: b[:], - nc: nc, + buf: fg, + nc: nc, + dbuf: [2][]byte{fg, nil}, } } +// flip replaces the active buffer with the background buffer +// this is a delayed flip that simply increases the buffer counter; +// the actual flip will be performed the next time we call `buffer.fill` +func (b *buffer) flip() { + b.flipcnt += 1 +} + // fill reads into the buffer until at least _need_ bytes are in it func (b *buffer) fill(need int) error { n := b.length + // fill data into its double-buffering target: if we've called + // flip on this buffer, we'll be copying to the background buffer, + // and then filling it with network data; otherwise we'll just move + // the contents of the current buffer to the front before filling it + dest := b.dbuf[b.flipcnt&1] + + // grow buffer if necessary to fit the whole packet. + if need > len(dest) { + // Round up to the next multiple of the default size + dest = make([]byte, ((need/defaultBufSize)+1)*defaultBufSize) - // move existing data to the beginning - if n > 0 && b.idx > 0 { - copy(b.buf[0:n], b.buf[b.idx:]) + // if the allocated buffer is not too large, move it to backing storage + // to prevent extra allocations on applications that perform large reads + if len(dest) <= maxCachedBufSize { + b.dbuf[b.flipcnt&1] = dest + } } - // grow buffer if necessary - // TODO: let the buffer shrink again at some point - // Maybe keep the org buf slice and swap back? - if need > len(b.buf) { - // Round up to the next multiple of the default size - newBuf := make([]byte, ((need/defaultBufSize)+1)*defaultBufSize) - copy(newBuf, b.buf) - b.buf = newBuf + // if we're filling the fg buffer, move the existing data to the start of it. + // if we're filling the bg buffer, copy over the data + if n > 0 { + copy(dest[:n], b.buf[b.idx:]) } + b.buf = dest b.idx = 0 for { @@ -105,43 +127,56 @@ func (b *buffer) readNext(need int) ([]byte, error) { return b.buf[offset:b.idx], nil } -// returns a buffer with the requested size. +// takeBuffer returns a buffer with the requested size. // If possible, a slice from the existing buffer is returned. // Otherwise a bigger buffer is made. // Only one buffer (total) can be used at a time. -func (b *buffer) takeBuffer(length int) []byte { +func (b *buffer) takeBuffer(length int) ([]byte, error) { if b.length > 0 { - return nil + return nil, ErrBusyBuffer } // test (cheap) general case first - if length <= defaultBufSize || length <= cap(b.buf) { - return b.buf[:length] + if length <= cap(b.buf) { + return b.buf[:length], nil } if length < maxPacketSize { b.buf = make([]byte, length) - return b.buf + return b.buf, nil } - return make([]byte, length) + + // buffer is larger than we want to store. + return make([]byte, length), nil } -// shortcut which can be used if the requested buffer is guaranteed to be -// smaller than defaultBufSize +// takeSmallBuffer is shortcut which can be used if length is +// known to be smaller than defaultBufSize. // Only one buffer (total) can be used at a time. -func (b *buffer) takeSmallBuffer(length int) []byte { +func (b *buffer) takeSmallBuffer(length int) ([]byte, error) { if b.length > 0 { - return nil + return nil, ErrBusyBuffer } - return b.buf[:length] + return b.buf[:length], nil } // takeCompleteBuffer returns the complete existing buffer. // This can be used if the necessary buffer size is unknown. +// cap and len of the returned buffer will be equal. // Only one buffer (total) can be used at a time. -func (b *buffer) takeCompleteBuffer() []byte { +func (b *buffer) takeCompleteBuffer() ([]byte, error) { + if b.length > 0 { + return nil, ErrBusyBuffer + } + return b.buf, nil +} + +// store stores buf, an updated buffer, if its suitable to do so. +func (b *buffer) store(buf []byte) error { if b.length > 0 { - return nil + return ErrBusyBuffer + } else if cap(buf) <= maxPacketSize && cap(buf) > cap(b.buf) { + b.buf = buf[:cap(buf)] } - return b.buf + return nil } |