From aa7a13a1c1613f4c3ce4b9494927d97ffc61053c Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Tue, 27 Feb 2018 00:21:19 +0100
Subject: [PATCH] Pruner: parallel pruning

refs #62
---
 cmd/prune.go | 95 +++++++++++++++++++++++++++++++---------------------
 1 file changed, 57 insertions(+), 38 deletions(-)

diff --git a/cmd/prune.go b/cmd/prune.go
index 73ea7e1..2adb14f 100644
--- a/cmd/prune.go
+++ b/cmd/prune.go
@@ -3,7 +3,9 @@ package cmd
 import (
 	"context"
 	"fmt"
+	"github.com/zrepl/zrepl/util"
 	"github.com/zrepl/zrepl/zfs"
+	"sync"
 	"time"
 )
 
@@ -23,9 +25,8 @@ type PruneResult struct {
 	Remove     []zfs.FilesystemVersion
 }
 
+// FIXME must not call p.task.Enter because it runs in parallel
 func (p *Pruner) filterFilesystems() (filesystems []*zfs.DatasetPath, stop bool) {
-	p.task.Enter("filter_fs")
-	defer p.task.Finish()
 	filesystems, err := zfs.ZFSListMapping(p.DatasetFilter)
 	if err != nil {
 		p.task.Log().WithError(err).Error("error applying filesystem filter")
@@ -38,9 +39,8 @@ func (p *Pruner) filterFilesystems() (filesystems []*zfs.DatasetPath, stop bool)
 	return filesystems, false
 }
 
+// FIXME must not call p.task.Enter because it runs in parallel
 func (p *Pruner) filterVersions(fs *zfs.DatasetPath) (fsversions []zfs.FilesystemVersion, stop bool) {
-	p.task.Enter("filter_versions")
-	defer p.task.Finish()
 	log := p.task.Log().WithField(logFSField, fs.ToString())
 
 	filter := NewPrefixFilter(p.SnapshotPrefix)
@@ -56,9 +56,8 @@ func (p *Pruner) filterVersions(fs *zfs.DatasetPath) (fsversions []zfs.Filesyste
 	return fsversions, false
 }
 
-func (p *Pruner) pruneFilesystem(fs *zfs.DatasetPath) (r PruneResult, valid bool) {
-	p.task.Enter("prune_fs")
-	defer p.task.Finish()
+// FIXME must not call p.task.Enter because it runs in parallel
+func (p *Pruner) pruneFilesystem(fs *zfs.DatasetPath, destroySemaphore util.Semaphore) (r PruneResult, valid bool) {
 	log := p.task.Log().WithField(logFSField, fs.ToString())
 
 	fsversions, stop := p.filterVersions(fs)
@@ -66,9 +65,7 @@ func (p *Pruner) pruneFilesystem(fs *zfs.DatasetPath) (r PruneResult, valid bool
 		return
 	}
 
-	p.task.Enter("prune_policy")
 	keep, remove, err := p.PrunePolicy.Prune(fs, fsversions)
-	p.task.Finish()
 	if err != nil {
 		log.WithError(err).Error("error evaluating prune policy")
 		return
@@ -81,33 +78,37 @@ func (p *Pruner) pruneFilesystem(fs *zfs.DatasetPath) (r PruneResult, valid bool
 
 	r = PruneResult{fs, fsversions, keep, remove}
 
-	makeFields := func(v zfs.FilesystemVersion) (fields map[string]interface{}) {
-		fields = make(map[string]interface{})
-		fields["version"] = v.ToAbsPath(fs)
-		timeSince := v.Creation.Sub(p.Now)
-		fields["age_ns"] = timeSince
-		const day time.Duration = 24 * time.Hour
-		days := timeSince / day
-		remainder := timeSince % day
-		fields["age_str"] = fmt.Sprintf("%dd%s", days, remainder)
-		return
-	}
+	var wg sync.WaitGroup
+	for v := range remove {
+		wg.Add(1)
+		go func(v zfs.FilesystemVersion) {
+			defer wg.Done()
+			// log fields
+			fields := make(map[string]interface{})
+			fields["version"] = v.ToAbsPath(fs)
+			timeSince := v.Creation.Sub(p.Now)
+			fields["age_ns"] = timeSince
+			const day time.Duration = 24 * time.Hour
+			days := timeSince / day
+			remainder := timeSince % day
+			fields["age_str"] = fmt.Sprintf("%dd%s", days, remainder)
 
-	for _, v := range remove {
-		fields := makeFields(v)
-		log.WithFields(fields).Info("destroying version")
-		// echo what we'll do and exec zfs destroy if not dry run
-		// TODO special handling for EBUSY (zfs hold)
-		// TODO error handling for clones? just echo to cli, skip over, and exit with non-zero status code (we're idempotent)
-		if !p.DryRun {
-			p.task.Enter("destroy")
-			err := zfs.ZFSDestroyFilesystemVersion(fs, v)
-			p.task.Finish()
-			if err != nil {
-				log.WithFields(fields).WithError(err).Error("error destroying version")
+			log.WithFields(fields).Info("destroying version")
+			// echo what we'll do and exec zfs destroy if not dry run
+			// TODO special handling for EBUSY (zfs hold)
+			// TODO error handling for clones? just echo to cli, skip over, and exit with non-zero status code (we're idempotent)
+			if !p.DryRun {
+				destroySemaphore.Down()
+				err := zfs.ZFSDestroyFilesystemVersion(fs, v)
+				destroySemaphore.Up()
+				if err != nil {
+					log.WithFields(fields).WithError(err).Error("error destroying version")
+				}
 			}
-		}
+		}(remove[v])
 	}
+	wg.Wait()
+
 	return r, true
 }
 
@@ -124,13 +125,31 @@ func (p *Pruner) Run(ctx context.Context) (r []PruneResult, err error) {
 		return
 	}
 
-	r = make([]PruneResult, 0, len(filesystems))
+	maxConcurrentDestroy := len(filesystems)
+	p.task.Log().WithField("max_concurrent_destroy", maxConcurrentDestroy).Info("begin concurrent destroy")
+	destroySem := util.NewSemaphore(maxConcurrentDestroy)
 
+	resChan := make(chan PruneResult, len(filesystems))
+	var wg sync.WaitGroup
 	for _, fs := range filesystems {
-		res, ok := p.pruneFilesystem(fs)
-		if ok {
-			r = append(r, res)
-		}
+		wg.Add(1)
+		go func(fs *zfs.DatasetPath) {
+			defer wg.Done()
+			res, ok := p.pruneFilesystem(fs, destroySem)
+			if ok {
+				resChan <- res
+			}
+
+		}(fs)
+	}
+	wg.Wait()
+	close(resChan)
+
+	p.task.Log().Info("destroys done")
+
+	r = make([]PruneResult, 0, len(filesystems))
+	for res := range resChan {
+		r = append(r, res)
 	}
 
 	return