Lock now takes a context and should honor cancellation

config.go

@@ -388,7 +388,7 @@ func (cfg *Config) obtainWithIssuer(ctx context.Context, issuer Issuer, name str
 
 	// ensure idempotency of the obtain operation for this name
 	lockKey := cfg.lockKey("cert_acme", name)
-	err := obtainLock(cfg.Storage, lockKey)
+	err := acquireLock(ctx, cfg.Storage, lockKey)
 	if err != nil {
 		return err
 	}
@@ -474,7 +474,7 @@ func (cfg *Config) renewWithIssuer(ctx context.Context, issuer Issuer, name stri
 
 	// ensure idempotency of the renew operation for this name
 	lockKey := cfg.lockKey("cert_acme", name)
-	err := obtainLock(cfg.Storage, lockKey)
+	err := acquireLock(ctx, cfg.Storage, lockKey)
 	if err != nil {
 		return err
 	}

filestorage.go

@@ -15,6 +15,7 @@
 package certmagic
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -124,7 +125,7 @@ func (fs *FileStorage) Filename(key string) string {
 
 // Lock obtains a lock named by the given key. It blocks
 // until the lock can be obtained or an error is returned.
-func (fs *FileStorage) Lock(key string) error {
+func (fs *FileStorage) Lock(ctx context.Context, key string) error {
 	filename := fs.lockFilename(key)
 
 	for {
@@ -168,8 +169,13 @@ func (fs *FileStorage) Lock(key string) error {
 
 		default:
 			// lockfile exists and is not stale;
-			// just wait a moment and try again
-			time.Sleep(fileLockPollInterval)
+			// just wait a moment and try again,
+			// or return if context cancelled
+			select {
+			case <-time.After(fileLockPollInterval):
+			case <-ctx.Done():
+				return ctx.Err()
+			}
 		}
 	}
 }

storage.go

@@ -15,6 +15,7 @@
 package certmagic
 
 import (
+	"context"
 	"log"
 	"path"
 	"regexp"
@@ -86,8 +87,11 @@ type Locker interface {
 	// To prevent deadlocks, all implementations (where this concern
 	// is relevant) should put a reasonable expiration on the lock in
 	// case Unlock is unable to be called due to some sort of network
-	// failure or system crash.
-	Lock(key string) error
+	// failure or system crash. Additionally, implementations should
+	// honor context cancellation as much as possible (in case the
+	// caller wishes to give up and free resources before the lock
+	// can be obtained).
+	Lock(ctx context.Context, key string) error
 
 	// Unlock releases the lock for key. This method must ONLY be
 	// called after a successful call to Lock, and only after the
@@ -223,8 +227,8 @@ func CleanUpOwnLocks() {
 	}
 }
 
-func obtainLock(storage Storage, lockKey string) error {
-	err := storage.Lock(lockKey)
+func acquireLock(ctx context.Context, storage Storage, lockKey string) error {
+	err := storage.Lock(ctx, lockKey)
 	if err == nil {
 		locksMu.Lock()
 		locks[lockKey] = storage