Merge 8a170e4 into 0a003e9

lib/prometheus/client/data_stores/direct_file_store.rb

@@ -154,7 +154,12 @@ def store_key(labels)
           end
 
           def internal_store
-            @internal_store ||= FileMappedDict.new(filemap_filename)
+            if @store_opened_by_pid != process_id
+              @store_opened_by_pid = process_id
+              @internal_store = FileMappedDict.new(filemap_filename)
+            else
+              @internal_store
+            end
           end
 
           # Filename for this metric's PStore (one per process)

spec/prometheus/client/data_stores/direct_file_store_spec.rb

@@ -57,6 +57,18 @@
     ms2.increment(labels: {}, by: 1)
   end
 
+  context "when process is forked" do
+    it "opens a new internal store to avoid two processes using the same file" do
+      allow(Process).to receive(:pid).and_return(12345)
+      metric_store = subject.for_metric(:metric_name, metric_type: :counter)
+      metric_store.increment(labels: {}, by: 1)
+
+      allow(Process).to receive(:pid).and_return(23456)
+      metric_store.increment(labels: {}, by: 1)
+      expect(Dir.glob('/tmp/prometheus_test/*').size).to eq(2)
+      expect(metric_store.all_values).to eq({} => 2.0)
+    end
+  end
 
   context "for a non-gauge metric" do
     it "sums values from different processes by default" do