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From: =?UTF-8?Q?Ren=c3=a9_Berber?= <rene DOT berber AT gmail DOT com>
Subject: Re: Fork and Windows Heap
Date: Wed, 15 Jun 2016 21:48:43 -0500
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References: <D38743FD.926E%billziss AT navimatics DOT com>
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In-Reply-To: <D38743FD.926E%billziss@navimatics.com>

On 6/15/2016 7:42 PM, Bill Zissimopoulos wrote:

[snip]
> WinFsp consists of an FSD (file system driver) and a DLL component. The
> WinFsp DLL uses the Windows heap functions to manage memory
> (HeapAlloc/HeapFree). It seems that the Windows heap is not properly
> cloned after a fork, which leads to the crash I am experiencing. I have
> the following questions:
> 
> (1) Is my assumption that Windows heaps are not properly cloned after a
> fork correct? A 2011 post [2] seems to suggest so.
> (2) Is there any workaround that the WinFsp DLL can use to get around this
> limitation and work properly after a fork? The obvious answer would be to
> have the DLL use Cygwin's malloc/free and this is indeed possible within
> the DLL's FUSE layer, but not workable elsewhere.

Those are the wrong questions: you shouldn't be mixing Windows and Unix
(SuSv4, Posix) APIs, and by your description you are trying a Windows
port, mixing it with probably the base, and expecting it to work on
Cygwin, that's a no-go from the start.

Unix software usually requires no porting, or very little to account for
libc implementations (glibc in Linux, newlib in Cygwin), and the Windows
environment.

I think you have 2 options:

1. Keep the Windows port and use the cross-compiler tools to create
Windows native binaries.  That means: forget about fork, start using the
spawn family of functions, i.e. _wspawnvp.  Of course the result will
work independently of Cygwin, daemons are called services (and created
differently).

2. Keep the base Unix version for everything.  Fork/exec works fine,
daemon works fine but you'll have to use cygrunsrv to install the daemon
as service.

You should read the documentation:

https://cygwin.com/cygwin-ug-net/highlights.html#ov-hi-ansiclib

Hope this helps.
-- 
René Berber


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