From a7dbf32c538db8d57b8c0a4088934ba5c0ec431d Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Thu, 8 Mar 2018 12:16:18 +0000
Subject: [PATCH] cache: Implement --cache-db-wait-time flag

This can be used to make the cache wait for other running cache
backends to finish rather than erroring after 1 second.
---
 backend/cache/cache.go              |  3 +++
 backend/cache/storage_persistent.go |  2 +-
 docs/content/cache.md               | 10 ++++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/backend/cache/cache.go b/backend/cache/cache.go
index d25e83892..a554ec316 100644
--- a/backend/cache/cache.go
+++ b/backend/cache/cache.go
@@ -50,6 +50,8 @@ const (
 	DefCacheWrites = false
 	// DefCacheTmpWaitTime says how long should files be stored in local cache before being uploaded
 	DefCacheTmpWaitTime = "15m"
+	// DefCacheDbWaitTime defines how long the cache backend should wait for the DB to be available
+	DefCacheDbWaitTime = 1 * time.Second
 )
 
 // Globals
@@ -69,6 +71,7 @@ var (
 	cacheStoreWrites        = flags.BoolP("cache-writes", "", DefCacheWrites, "Will cache file data on writes through the FS")
 	cacheTempWritePath      = flags.StringP("cache-tmp-upload-path", "", "", "Directory to keep temporary files until they are uploaded to the cloud storage")
 	cacheTempWaitTime       = flags.StringP("cache-tmp-wait-time", "", DefCacheTmpWaitTime, "How long should files be stored in local cache before being uploaded")
+	cacheDbWaitTime         = flags.DurationP("cache-db-wait-time", "", DefCacheDbWaitTime, "How long to wait for the DB to be available - 0 is unlimited")
 )
 
 // Register with Fs
diff --git a/backend/cache/storage_persistent.go b/backend/cache/storage_persistent.go
index bbc77c2a4..894d79e92 100644
--- a/backend/cache/storage_persistent.go
+++ b/backend/cache/storage_persistent.go
@@ -122,7 +122,7 @@ func (b *Persistent) connect() error {
 	if err != nil {
 		return errors.Wrapf(err, "failed to create a data directory %q", b.dataPath)
 	}
-	b.db, err = bolt.Open(b.dbPath, 0644, &bolt.Options{Timeout: 1 * time.Second})
+	b.db, err = bolt.Open(b.dbPath, 0644, &bolt.Options{Timeout: *cacheDbWaitTime})
 	if err != nil {
 		return errors.Wrapf(err, "failed to open a cache connection to %q", b.dbPath)
 	}
diff --git a/docs/content/cache.md b/docs/content/cache.md
index 49cfc27a2..23a9d947c 100644
--- a/docs/content/cache.md
+++ b/docs/content/cache.md
@@ -397,3 +397,13 @@ Note that only one file is uploaded at a time and it can take longer to
 start the upload if a queue formed for this purpose.
 
 **Default**: 15m
+
+#### --cache-db-wait-time=DURATION ####
+
+Only one process can have the DB open at any one time, so rclone waits
+for this duration for the DB to become available before it gives an
+error.
+
+If you set it to 0 then it will wait forever.
+
+**Default**: 1s