From 15fe998c68b3980cc064feabfe770eded2e77fde Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Wed, 14 Oct 2020 14:02:19 -0700
Subject: [PATCH] add an timed-cache blockstore

This blockstore lets us write to a temporary scratch location where blocks older
than the specified cache time are automatically cleared.
---
 lib/timedbs/timedbs.go | 156 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 156 insertions(+)
 create mode 100644 lib/timedbs/timedbs.go

diff --git a/lib/timedbs/timedbs.go b/lib/timedbs/timedbs.go
new file mode 100644
index 000000000..bb03a59e9
--- /dev/null
+++ b/lib/timedbs/timedbs.go
@@ -0,0 +1,156 @@
+package timedbs
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	blocks "github.com/ipfs/go-block-format"
+	"github.com/ipfs/go-cid"
+	"go.uber.org/multierr"
+
+	"github.com/filecoin-project/lotus/build"
+	"github.com/filecoin-project/lotus/lib/blockstore"
+)
+
+// TimedCacheBS is a blockstore that keeps blocks for at least the specified
+// caching interval before discarding them. Garbage collection must be started
+// and stopped by calling Start/Stop.
+//
+// Under the covers, it's implemented with an active and an inactive blockstore
+// that are rotated every cache time interval. This means all blocks will be
+// stored at most 2x the cache interval.
+type TimedCacheBS struct {
+	mu               sync.RWMutex
+	active, inactive blockstore.MemStore
+
+	interval time.Duration
+	closeCh  chan struct{}
+}
+
+func NewTimedCacheBS(cacheTime time.Duration) *TimedCacheBS {
+	return &TimedCacheBS{
+		active:   blockstore.NewTemporary(),
+		inactive: blockstore.NewTemporary(),
+		interval: cacheTime,
+	}
+}
+
+func (t *TimedCacheBS) Start(ctx context.Context) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.closeCh != nil {
+		return fmt.Errorf("already started")
+	}
+	t.closeCh = make(chan struct{})
+	go func() {
+		ticker := build.Clock.Ticker(t.interval)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				t.rotate()
+			case <-t.closeCh:
+				return
+			}
+		}
+	}()
+	return nil
+}
+
+func (t *TimedCacheBS) Stop(ctx context.Context) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.closeCh == nil {
+		return fmt.Errorf("not started started")
+	}
+	select {
+	case <-t.closeCh:
+		// already closed
+	default:
+		close(t.closeCh)
+	}
+	return nil
+}
+
+func (t *TimedCacheBS) rotate() {
+	newBs := blockstore.NewTemporary()
+
+	t.mu.Lock()
+	t.inactive, t.active = t.active, newBs
+	t.mu.Unlock()
+}
+
+func (t *TimedCacheBS) Put(b blocks.Block) error {
+	// Don't check the inactive set here. We want to keep this block for at
+	// least one interval.
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.active.Put(b)
+}
+
+func (t *TimedCacheBS) PutMany(bs []blocks.Block) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.active.PutMany(bs)
+}
+
+func (t *TimedCacheBS) Get(k cid.Cid) (blocks.Block, error) {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+	b, err := t.active.Get(k)
+	if err == blockstore.ErrNotFound {
+		b, err = t.inactive.Get(k)
+	}
+	return b, err
+}
+
+func (t *TimedCacheBS) GetSize(k cid.Cid) (int, error) {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+	size, err := t.active.GetSize(k)
+	if err == blockstore.ErrNotFound {
+		size, err = t.inactive.GetSize(k)
+	}
+	return size, err
+}
+
+func (t *TimedCacheBS) Has(k cid.Cid) (bool, error) {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+	if has, err := t.active.Has(k); err != nil {
+		return false, err
+	} else if has {
+		return true, nil
+	}
+	return t.inactive.Has(k)
+}
+
+func (t *TimedCacheBS) HashOnRead(_ bool) {
+	// no-op
+}
+
+func (t *TimedCacheBS) DeleteBlock(k cid.Cid) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return multierr.Combine(t.active.DeleteBlock(k), t.inactive.DeleteBlock(k))
+}
+
+func (t *TimedCacheBS) AllKeysChan(ctx context.Context) (<-chan cid.Cid, error) {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+
+	ch := make(chan cid.Cid, len(t.active)+len(t.inactive))
+	for c := range t.active {
+		ch <- c
+	}
+	for c := range t.inactive {
+		if _, ok := t.active[c]; ok {
+			continue
+		}
+		ch <- c
+	}
+	close(ch)
+	return ch, nil
+}