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Re: signals on windows

From: Marsh Ray <marsh-pg(at)mysteray(dot)com>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Andrew Dunstan <andrew(at)dunslane(dot)net>,pgsql-hackers-win32 <pgsql-hackers-win32(at)postgresql(dot)org>
Subject: Re: signals on windows
Date: 2003-10-10 04:09:40
Message-ID: 3F863104.2080208@mysteray.com (view raw or flat)
Thread:
Lists: pgsql-hackers-win32
Hi,
This MS documentation looks like it's slightly retro. I've been trying 
to decypher this stuff myself for a decade, so I might offer some points:.

>Andrew Dunstan wrote:
>  
>
>> *   Note   SIGINT is not supported for any Win32 application, including
>>*   Windows 98/Me and Windows NT/2000/XP.When a CTRL+C interrupt occurs,
>> *   Win32 operating systems generate a new thread to specifically handle
>> *   that interrupt. This can cause a single-thread application such as 
>>UNIX,
>> *   to become multithreaded, resulting in unexpected behavior.
>>
Odd. First they say it's not supported, then they go on to define how it 
works. Probably what they mean is that Win32 _GUI_ applications have no 
way to have receive SIGINT from Ctrl+C, because that's handled as just 
another keystroke by the GUI system (sometimes you'll see the older 
documentation use Win32 as a term implying GUI).  Win32 console apps 
appear to respond to Ctrl+C much like unices do.

Since Win32 will create a new thread for you, if you prepare your app 
for that, I don't see a reason you can't make pure Win32 system calls 
from that thread. You mainly want to be careful to not confuse a 
single-threaded C runtime. Note that the doc 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclib/html/_CRT_signal.asp 
says not to "use any function that generates a system call (e.g., 
*_getcwd*, *time*)", it doesn't say not to make system calls themselves. 
It doesn't look like a "signal" is not a kernel primitive on NT, it's a 
feature of the CRT implemented in userspace with lower-level OS primitives.

>> * I have no idea how to handle this. (Strange they call UNIX an 
>>application!)
>> * So this will need some testing on Windows.
>> * One alternative might be to set a flag that we periodically check for.
>>
A kernel Event 
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/createevent.asp) 
is a common tool for this sort of thing.

- Marsh


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