fixup! Add DataStores::DirectFileStore

lib/prometheus/client/data_stores/direct_file_store.rb

@@ -112,20 +112,18 @@ def all_values
             stores_for_metric.each do |file_path|
               begin
                 store = FileMappedDict.new(file_path, true)
-                store.with_file_lock do
-                  store.all_values.each do |(labelset_qs, v)|
-                    # Labels come as a query string, and CGI::parse returns arrays for each key
-                    # "foo=bar&x=y" => { "foo" => ["bar"], "x" => ["y"] }
-                    # Turn the keys back into symbols, and remove the arrays
-                    label_set = CGI::parse(labelset_qs).map do |k, vs|
-                      [k.to_sym, vs.first]
-                    end.to_h
-
-                    stores_data[label_set] << v
-                  end
+                store.all_values.each do |(labelset_qs, v)|
+                  # Labels come as a query string, and CGI::parse returns arrays for each key
+                  # "foo=bar&x=y" => { "foo" => ["bar"], "x" => ["y"] }
+                  # Turn the keys back into symbols, and remove the arrays
+                  label_set = CGI::parse(labelset_qs).map do |k, vs|
+                    [k.to_sym, vs.first]
+                  end.to_h
+
+                  stores_data[label_set] << v
                 end
               ensure
-                store.close
+                store.close if store
               end
             end
 
@@ -192,25 +190,34 @@ class FileMappedDict
           attr_reader :capacity, :used, :positions
 
           def initialize(filename, readonly = false)
+            @positions = {}
+            @used = 0
+
             open_file(filename, readonly)
-            @capacity = @f.size
+            @used = @f.read(4).unpack('l')[0] if @capacity > 0
 
-            @positions = {}
-            @used = @f.read(4).unpack('l')[0]
-            if @used == 0
-              @used = 8
-              @f.seek(0)
-              @f.write([@used].pack('l'))
+            if @used > 0
+              # File already has data. Read the existing values
+              with_file_lock do
+                read_all_values.each do |key, _, pos|
+                  @positions[key] = pos
+                end
+              end
             else
-              read_all_values.each do |key, _, pos|
-                @positions[key] = pos
+              # File is empty. Init the `used` counter, if we're in write mode
+              if !readonly
+                @used = 8
+                @f.seek(0)
+                @f.write([@used].pack('l'))
               end
             end
           end
 
           # Yield (key, value, pos). No locking is performed.
           def all_values
-            read_all_values.map { |k, v, p| [k, v] }
+            with_file_lock do
+              read_all_values.map { |k, v, p| [k, v] }
+            end
           end
 
           def read_value(key)
@@ -260,6 +267,7 @@ def open_file(filename, readonly)
             if @f.size == 0 && !readonly
               resize_file(INITIAL_FILE_SIZE)
             end
+            @capacity = @f.size
           end
 
           def resize_file(new_capacity)