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Sync from PG in parallel using an in-memory backpressured buffer
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,103 @@ | ||
| package main | ||
|
|
||
| import ( | ||
| "errors" | ||
| "io" | ||
| "sync" | ||
| ) | ||
|
|
||
| type CappedBuffer struct { | ||
| config *Config | ||
| maxSizeBytes int | ||
|
|
||
| buffer []byte | ||
| mutex sync.Mutex | ||
| conditionalSync *sync.Cond | ||
|
|
||
| closeOnceSync sync.Once | ||
| closed bool | ||
| } | ||
|
|
||
| func NewCappedBuffer(maxSizeBytes int, config *Config) *CappedBuffer { | ||
| sizedBuffer := &CappedBuffer{ | ||
| config: config, | ||
| buffer: make([]byte, 0, maxSizeBytes), | ||
| maxSizeBytes: maxSizeBytes, | ||
| } | ||
| sizedBuffer.conditionalSync = sync.NewCond(&sizedBuffer.mutex) | ||
| return sizedBuffer | ||
| } | ||
|
|
||
| // Implements io.Writer | ||
| func (buf *CappedBuffer) Write(payload []byte) (writtenBytes int, err error) { | ||
| if len(payload) == 0 { | ||
| return 0, nil | ||
| } | ||
|
|
||
| buf.mutex.Lock() | ||
| defer buf.mutex.Unlock() | ||
|
|
||
| if buf.closed { | ||
| return 0, errors.New("buffer is closed") | ||
| } | ||
|
|
||
| for len(buf.buffer)+len(payload) > buf.maxSizeBytes && !buf.closed { | ||
| LogTrace(buf.config, ">> Waiting for more space in capped buffer...") | ||
| buf.conditionalSync.Wait() // Wait for the reader | ||
| } | ||
|
|
||
| // Check again if buffer was closed while waiting | ||
| if buf.closed { | ||
| return 0, errors.New("buffer is closed") | ||
| } | ||
|
|
||
| writtenBytes = len(payload) | ||
| buf.buffer = append(buf.buffer, payload...) | ||
| LogTrace(buf.config, ">> Writing", writtenBytes, "bytes to capped buffer...") | ||
|
|
||
| buf.conditionalSync.Broadcast() // Notify the reader that new data is available | ||
|
|
||
| return writtenBytes, nil | ||
| } | ||
|
|
||
| // Implements io.Reader | ||
| func (buf *CappedBuffer) Read(payload []byte) (readBytes int, err error) { | ||
| if len(payload) == 0 { | ||
| return 0, nil | ||
| } | ||
|
|
||
| buf.mutex.Lock() | ||
| defer buf.mutex.Unlock() | ||
|
|
||
| for len(buf.buffer) == 0 && !buf.closed { | ||
| LogTrace(buf.config, "<< Waiting for more data in capped buffer...") | ||
| buf.conditionalSync.Wait() // Wait for the writer | ||
| } | ||
|
|
||
| if len(buf.buffer) == 0 && buf.closed { | ||
| return 0, io.EOF | ||
| } | ||
|
|
||
| maxReadBytes := len(payload) | ||
| readBytes = copy(payload, buf.buffer) | ||
| buf.buffer = buf.buffer[readBytes:] | ||
| LogTrace(buf.config, "<< Reading "+IntToString(readBytes)+"/"+IntToString(maxReadBytes)+" bytes from capped buffer...") | ||
|
|
||
| buf.conditionalSync.Broadcast() // Notify the writer that space is now available | ||
|
|
||
| return readBytes, nil | ||
| } | ||
|
|
||
| func (buf *CappedBuffer) Close() error { | ||
| buf.closeOnceSync.Do(func() { | ||
| buf.mutex.Lock() | ||
|
|
||
| LogTrace(buf.config, "== Closing capped buffer...") | ||
| buf.closed = true | ||
|
|
||
| buf.conditionalSync.Broadcast() // Wake up any waiting writers/readers | ||
|
|
||
| buf.mutex.Unlock() | ||
| }) | ||
| return nil | ||
| } |
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