[perfstats] do not register the same file twice in the same process

Summary:
Only one instance will win in the end so it's not useful to double register.
Log when that happens. Currently it happens in the Java tests on
`InferBuiltins` but I don't understand why so I left it alone.

Reviewed By: jberdine

Differential Revision: D5217928

fbshipit-source-id: dc7ccca

infer/src/backend/PerfStats.ml

@@ -142,21 +142,29 @@ let stats () =
     attributes_table = at
   }
 
-let register_report_at_exit file =
-  if not Config.buck_cache_mode then
-    Epilogues.register ~f:(fun () ->
-        try
-          let json_stats = to_json (stats ()) in
-          try
-            Unix.mkdir_p (Filename.dirname file);
-            Utils.write_file_with_locking file ~f:(fun stats_oc ->
-                Yojson.Basic.pretty_to_channel stats_oc json_stats;
-              );
-          with exc ->
-            L.internal_error "Info: failed to write stats to %s@\n%s@\n%s@\n%s@."
-              file (Exn.to_string exc) (Yojson.Basic.pretty_to_string json_stats)
-              (Printexc.get_backtrace ())
-        with exc ->
-          L.internal_error "Info: failed to compute stats for %s@\n%s@\n%s@."
-            file (Exn.to_string exc) (Printexc.get_backtrace ())
-      ) ("stats reporting in " ^ file)
+let report_at_exit file () =
+  try
+    let json_stats = to_json (stats ()) in
+    try
+      Unix.mkdir_p (Filename.dirname file);
+      (* the same report may be registered across different infer processes *)
+      Utils.write_file_with_locking file ~f:(fun stats_oc ->
+          Yojson.Basic.pretty_to_channel stats_oc json_stats;
+        );
+    with exc ->
+      L.internal_error "Info: failed to write stats to %s@\n%s@\n%s@\n%s@."
+        file (Exn.to_string exc) (Yojson.Basic.pretty_to_string json_stats)
+        (Printexc.get_backtrace ())
+  with exc ->
+    L.internal_error "Info: failed to compute stats for %s@\n%s@\n%s@."
+      file (Exn.to_string exc) (Printexc.get_backtrace ())
+
+let register_report_at_exit =
+  (* take care of not double-registering the same perf stat report *)
+  let registered_files = String.Table.create ~size:4 () in
+  fun file ->
+    if not (Hashtbl.mem registered_files file) then (
+      String.Table.set registered_files ~key:file ~data:();
+      if not Config.buck_cache_mode then
+        Epilogues.register ~f:(report_at_exit file) ("stats reporting in " ^ file)
+    )

infer/src/java/jClasspath.mli

@@ -27,7 +27,7 @@ val is_model : Typ.Procname.t -> bool
 
 val split_classpath : string -> string list
 
-(** map entry for source files with potential basname collision within the same compiler call *)
+(** map entry for source files with potential basename collision within the same compiler call *)
 type file_entry =
   | Singleton of SourceFile.t
   | Duplicate of (string * SourceFile.t) list