From d2eeee7a12abbfaf1fba21dd664493581c6529b4 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Thu, 21 Feb 2019 20:10:17 -0800
Subject: [PATCH] pool/write: adds Write pool

---
 pool/write.go | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 pool/write.go

diff --git a/pool/write.go b/pool/write.go
new file mode 100644
index 00000000..1322a289
--- /dev/null
+++ b/pool/write.go
@@ -0,0 +1,100 @@
+package pool
+
+import (
+	"bytes"
+	"time"
+
+	"github.com/lightningnetwork/lnd/buffer"
+)
+
+// Write is a worker pool specifically designed for sharing access to
+// buffer.Write objects amongst a set of worker goroutines. This enables an
+// application to limit the total number of buffer.Write objects allocated at
+// any given time.
+type Write struct {
+	workerPool *Worker
+	bufferPool *WriteBuffer
+}
+
+// NewWrite creates a Write pool, using an underlying Writebuffer pool to
+// recycle buffer.Write objects accross the lifetime of the Write pool's
+// workers.
+func NewWrite(writeBufferPool *WriteBuffer, numWorkers int,
+	workerTimeout time.Duration) *Write {
+
+	w := &Write{
+		bufferPool: writeBufferPool,
+	}
+	w.workerPool = NewWorker(&WorkerConfig{
+		NewWorkerState: w.newWorkerState,
+		NumWorkers:     numWorkers,
+		WorkerTimeout:  workerTimeout,
+	})
+
+	return w
+}
+
+// Start safely spins up the Write pool.
+func (w *Write) Start() error {
+	return w.workerPool.Start()
+}
+
+// Stop safely shuts down the Write pool.
+func (w *Write) Stop() error {
+	return w.workerPool.Stop()
+}
+
+// Submit accepts a function closure that provides access to a fresh
+// bytes.Buffer backed by a buffer.Write object. The function's execution will
+// be allocated to one of the underlying Worker pool's goroutines.
+func (w *Write) Submit(inner func(*bytes.Buffer) error) error {
+	return w.workerPool.Submit(func(s WorkerState) error {
+		state := s.(*writeWorkerState)
+		return inner(state.buf)
+	})
+}
+
+// writeWorkerState is the per-goroutine state maintained by a Write pool's
+// goroutines.
+type writeWorkerState struct {
+	// bufferPool is the pool to which the writeBuf will be returned when
+	// the goroutine exits.
+	bufferPool *WriteBuffer
+
+	// writeBuf is the buffer taken from the bufferPool on initialization,
+	// which will be used to back the buf object provided to any tasks that
+	// the goroutine processes before exiting.
+	writeBuf *buffer.Write
+
+	// buf is a buffer backed by writeBuf, that can be written to by tasks
+	// submitted to the Write pool. The buf will be reset between each task
+	// processed by a goroutine before exiting, and allows the task
+	// submitters to interact with the writeBuf as if it were an io.Writer.
+	buf *bytes.Buffer
+}
+
+// newWorkerState initializes a new writeWorkerState, which will be called
+// whenever a new goroutine is allocated to begin processing write tasks.
+func (w *Write) newWorkerState() WorkerState {
+	writeBuf := w.bufferPool.Take()
+
+	return &writeWorkerState{
+		bufferPool: w.bufferPool,
+		writeBuf:   writeBuf,
+		buf:        bytes.NewBuffer(writeBuf[0:0:len(writeBuf)]),
+	}
+}
+
+// Cleanup returns the writeBuf to the underlying buffer pool, and removes the
+// goroutine's reference to the readBuf and encapsulating buf.
+func (w *writeWorkerState) Cleanup() {
+	w.bufferPool.Return(w.writeBuf)
+	w.writeBuf = nil
+	w.buf = nil
+}
+
+// Reset resets the bytes.Buffer so that it is zero-length and has the capacity
+// of the underlying buffer.Write.k
+func (w *writeWorkerState) Reset() {
+	w.buf.Reset()
+}