move writing to REPL history file to behind a PID lock

Author: KristofferC

stdlib/REPL/Project.toml

@@ -2,14 +2,15 @@ name = "REPL"
 uuid = "3fa0cd96-eef1-5676-8a61-b3b8758bbffb"
 
 [deps]
+FileWatching = "7b1f6079-737a-58dc-b8bc-7a2ca5c1b5ee"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 Markdown = "d6f4376e-aef5-505a-96c1-9c027394607a"
 Sockets = "6462fe0b-24de-5631-8697-dd941f90decc"
 Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 
 [extras]
-Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
 test = ["Test", "Random"]

stdlib/REPL/src/REPL.jl

@@ -17,6 +17,7 @@ Base.Experimental.@optlevel 1
 
 using Base.Meta, Sockets
 import InteractiveUtils
+import FileWatching
 
 export
     AbstractREPL,
@@ -642,7 +643,6 @@ function add_history(hist::REPLHistoryProvider, s::PromptState)
     # mode: $mode
     $(replace(str, r"^"ms => "\t"))
     """
-    # TODO: write-lock history file
     try
         seekend(hist.history_file)
     catch err
@@ -651,8 +651,10 @@ function add_history(hist::REPLHistoryProvider, s::PromptState)
         # If this doesn't fix it (e.g. when file is deleted), we'll end up rethrowing anyway
         hist_open_file(hist)
     end
-    print(hist.history_file, entry)
-    flush(hist.history_file)
+    FileWatching.mkpidlock(hist.file_path  * ".pid", stale_age=3) do
+        print(hist.history_file, entry)
+        flush(hist.history_file)
+    end
     nothing
 end