[Ironpython-users] Recreate and compile a script in an existing engine instance?

Mon Jul 14 16:55:40 CEST 2014

Hi, Andrew,

According to my experiences, the FileSystemWatcher are only of limited use without additional precautions.

They fire "eventually" after a file modification took place (the write access happened). This does not imply that

1.     The modifying program has finished its modifications – it could be still issuing further write requests to complete its work.

2.     The modifying program has closed the file handle. (By default, windows blocks concurrent access to the files.)

3.     No one else has started modifying the file in the meantime (including the next "cycle of the original modifying program).

Most of the time, one wishes some "Notify me when the modifying program has closed the file handle, and atomically give me a file handle" event.

Best regards

Markus Schaber

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Von: Ironpython-users [mailto:ironpython-users-bounces+m.schaber=codesys.com at python.org] Im Auftrag von Andrew Stephens
Gesendet: Montag, 14. Juli 2014 16:13
An: Jeff Hardy
Cc: ironpython-users at python.org
Betreff: Re: [Ironpython-users] Recreate and compile a script in an existing engine instance?

I think I’ve found the cause of the problem. I recreate the script source and compile it within the FileSystemWatcher.Changed event. I can only assume that the file is still locked or is still being written to as this event fires - adding even a very small Thread.Sleep() seems to have fixed it.

From: Jeff Hardy [mailto:jdhardy at gmail.com]
Sent: 14 July 2014 13:03
To: Andrew Stephens
Cc: ironpython-users at python.org<mailto:ironpython-users at python.org>
Subject: Re: [Ironpython-users] Recreate and compile a script in an existing engine instance?

Smells like a bug, because this should work. Can you open an issue (https://ironpython.codeplex.com/WorkItem/Create) with a minimal test case that reproduces it?

- Jeff

On Fri, Jul 11, 2014 at 11:58 AM, Andrew Stephens <Andrew.Stephens at nu-ins.com<mailto:Andrew.Stephens at nu-ins.com>> wrote:
In C# I’m loading and compiling a script like this:-

            _engine = Python.CreateEngine();
            _scope = _engine.CreateScope();

            _scriptSource = _engine.CreateScriptSourceFromFile(filename, Encoding.UTF7, SourceCodeKind.Statements);
            _compiledScript = _scriptSource.Compile();

(At some point in time my application will run the script by calling _compiledScript.Execute(_scope).)

I’ve also got a FileSystemWatcher watching the script file. When the file changes I recreate the ScriptSource and compile, basically executing those last two lines again. When I do this, _scriptSource.Compile() throws an ArgumentException (“Invalid argument valueParameter name: start”). The stack trace is below. It works if I re-create *everything* – the engine, scope, script source, compile, but this seems a bit a wasteful. Am I missing something?

Stack trace:-
   at Microsoft.Scripting.Utils.ContractUtils.Requires(Boolean precondition, String paramName)
   at Microsoft.Scripting.SourceUnit.GetCodeLines(Int32 start, Int32 count)
   at Microsoft.Scripting.SourceUnit.GetCodeLine(Int32 line)
   at Microsoft.Scripting.SyntaxErrorException..ctor(String message, SourceUnit sourceUnit, SourceSpan span, Int32 errorCode, Severity severity)
   at Microsoft.Scripting.Hosting.ErrorListenerProxySink.Add(SourceUnit sourceUnit, String message, SourceSpan span, Int32 errorCode, Severity severity)
   at IronPython.Compiler.Parser.CreateParserWorker(CompilerContext context, PythonOptions options, Boolean verbatim)
   at IronPython.Compiler.Parser.CreateParser(CompilerContext context, PythonOptions options)
   at IronPython.Runtime.PythonContext.ParseAndBindAst(CompilerContext context)
   at IronPython.Runtime.PythonContext.CompilePythonCode(SourceUnit sourceUnit, CompilerOptions options, ErrorSink errorSink)
   at IronPython.Runtime.PythonContext.CompileSourceCode(SourceUnit sourceUnit, CompilerOptions options, ErrorSink errorSink)
   at Microsoft.Scripting.SourceUnit.Compile(CompilerOptions options, ErrorSink errorSink)
   at Microsoft.Scripting.SourceUnit.Compile(ErrorSink errorSink)
   at Microsoft.Scripting.Hosting.ScriptSource.CompileInternal(CompilerOptions compilerOptions, ErrorListener errorListener)
   at Microsoft.Scripting.Hosting.ScriptSource.Compile()

Andrew Stephens

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Disclaimer

This message is confidential and may contain privileged information and is protected by copyright. If you are not the intended recipient you should not copy or disclose this message to anyone but should kindly notify the sender and delete the message. Opinions, conclusions and other information in this message which do not relate to the official business of Nu Instruments Ltd shall be understood as neither given nor endorsed by it. No contracts shall be concluded by means of this email. Neither the Company nor the sender accepts any responsibility or liability for any loss or damage arising from the presence of any computer virus or similar harmful code contained in this email or attachment/s.  It is your responsibility to scan this email and any attachments. The Company reserves the right to access and disclose all messages sent over its email system.

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