Add cache maintenance locking

internal/projects/cache.go

@@ -51,6 +51,33 @@ func (c *Cache) Load() error {
 	return err
 }
 
+func (c *Cache) UnlockCache() {
+	c.log.Info("Unlocking cache")
+	if err := os.Remove(c.file + ".lock"); err != nil {
+		c.log.Fatal("Failed unlocking cache, manual rm may be necessary",
+			c.log.Args("error", err, "lockFile", c.file+".lock"),
+		)
+	}
+}
+
+func (c *Cache) LockCache() {
+	c.log.Info("Attempting to lock cache")
+	c.checkLock()
+
+	file, err := os.OpenFile(c.file+".lock", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0640)
+	defer file.Close()
+
+	if err != nil {
+		c.log.Fatal("Failed to lock cache", c.log.Args("error", err))
+	}
+}
+
+func (c *Cache) checkLock() {
+	if _, err := os.Stat(c.file + ".lock"); err == nil {
+		c.log.Fatal("Can't manage cache, already locked")
+	}
+}
+
 // Saves the current state of the cache to disk
 func (c *Cache) write() {
 	file, err := os.OpenFile(c.file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0640)