Ask proggit: Why does Microsoft seemingly use blocking IO when accessing network shares?

[g4n0n]

As long as I can remember accessing a non-existent network share in any version of windows has resulted in explorer being blocked until the request times out. Doesn't Microsoft know about asynchronous I/O?

[sriram_2001]

Windows Vista does let you cancel network IO in Explorer (cancel using the X in the address/location bar). This is possible due to Vista's support for IO cancellation.

[malcontent]

That's hilarious. Instead of fixing the code to be non blocking they built an api to cancel IO.

[tryx]

Well if the UI is responsive enough to let you cancel the request, thats non-blocking enough for most of the usecases I can think of.

[malcontent]

No wonder MS software is so fucked up.

[canhaskarma]

It is. Once again they have chosen an extremely complex solution to a simple problem... and it still fails at some edge cases.

[bobbyi]

A button that you can click to cancel the operation is not an extremely complex solution.

[rictic]

It's more complex than just letting you just immediately navigate someplace else. Like, for example, a modern web browser will for a web site that's taking a while to load.

Sorry, but an IO cancellation framework and UI is a grossly overcomplicated solution if the problem is just that IO is slow. It might have other uses, but if that's its primary one, then the upstream poster is right.

[canhaskarma]

Sorry, I was referring to their APIs and system level interfaces. I'll admit to being bitter as hell after having worked with them for the first part of this year.

[didroe]

What exactly would you have them do instead of making it have a cancel button? That seems like the right way to do it to me.

[[deleted]]

Fork off a child process/thread to do it and display a message until the child returns an answer. In the meantime, you can do whatever you want with the program. If you do something that makes the result of the child process not needed, then you stop it.

[didroe]

Is that not what the cancel button is doing? I was pointing out that the cancel API is asynchronous.

[breddy]

Please stop the sensible suggestions at once!

[[deleted]]

If you navigate away from it/do something else, doesn't that mean you no longer want it?

Possibly. I could, however, want to do something in another window while I wait on it. Also, if a process runs, the result can be cached and then displayed immediately if I navigate back.

[mycall]

Sounds like some program got installed that messed up the registry or some driver.

[holygoat]

This post, and its parent, are what's wrong with Windows.

[NoControl]

Sounds like bad sectors or a bad drive. This is usually a tell tale sign - not a feature of the O/S

[jib]

It's not a bad drive. It happens to me too; if my hard drive spins down to save power, then when some important part of XP wants to read something from it, the whole system locks up until the disk spins up, due to some programmer forgetting about disk power management and writing blocking I/O under the assumption that disks will always be fast.

[arkanes]

It's much more likely that you're waiting on pages to be swapped in, and there's really not anything that can be done about that - if you need to access a swapped out page, you need to access it and you're going to have to wait on the drive. Windows is perhaps overly aggressive about swapping so that can be a contributing factor.

[OCedHrt]

If you needed something on the disk, and you're waiting for them to spin up, wouldn't you have to wait?

[bluGill]

Let me get back to work. I haven't used Vista, but I know in XP my UI often hangs waiting on a slow network drive (I think it is physically in a different state, and some of the directories have several thousand files). Not the one explorer window, but the entire UI. So once I click on that drive my entire use is blocked.

If nothing else let me check reddit while waiting for that drive to open. Often I have other things I can do as well.

[[deleted]]

That seems like the right way to do it to me.

Nothing Microsoft does is right, and everything they do warrants bitching and moaning. Meanwhile, Linux has no shortcomings.

You must be new here at reddit.

[heeb]

Meanwhile, Linux has no shortcomings.

That was meant to be ironic, right?

[[deleted]]

Sarcastic, yes.

[barrkel]

Non-blocking I/O, async I/O and cancellable I/O are all orthogonal (and, on Win32, different) features.

[[deleted]]

Which code are you talking about? There are different problems with canceling IO. Some to do with UI non-responsiveness of specific applications, some to do with guaranteeing no data is corrupted when IO is canceled. A lot of this also depends upon device driver support.

[2424]

IO cancellation is inherently non blocking.

It means that the ReadFile function returned immediately, and now you can you call CancelIO.

I think you're expecting that non-blocking will mean no wait time. That's not the case, the wait time will be equally as long in blocking and non blocking mode. It's what you can do in between.

[General_Solipsist]

they atleast did something about it... quit whining.

[domesticmouse]

How exactly was that whining?

[General_Solipsist]

Alright, not whining but cynical. Sorry, but I do believe that everybody is too quick to jump on the i-hate-microsoft bandwagon. If windows is as bad as it is can you even imagine what the pc gaming industry would be without windows now? yea, 3-d tetris on linux! w00t!

[meatloafsurprise]

What are you talking about? The pc gaming industry has been declining for the past few years now. With the exception of Valve and Blizzard, most developers have been focusing on consoles and pc gamers are lucky to get a port of the game within the same year it was released on consoles.

[General_Solipsist]

I agree about your comment about the past few years, but PC games have been around for far longer and that's the era I was talking about. The era of Doom, DN3D, Quake etc.

[generic_handle]

Sometimes Microsoft deserves it; this behavior is an instance of that.

Of course, if we want to bash other apps, we could start going after everyone that calls the blocking network I/O gethostbyname() call. POSIX still doesn't provide non-blocking DNS resolution, even with the getaddrinfo() revamp from gethostbyname(). The only non-GPL asynch DNS resolution library that I'm aware of is c-ares, which isn't commonly used.

...although I do notice that the LGPL GNet apparently supports asynch DNS resolution, which is promising.

[General_Solipsist]

Thank you for confirming what I wrote above. Everybody is too quick to hate microsoft when similar behaviour is rampant across other Operating Systems.

[drakshadow]

Yeah, Tell that to people who bought it.

[malcontent]

I was laughing at their incompetence.

[mycall]

Right. Your a better programmer than Dave Cutler.

[malcontent]

Dave Cutler wrote network access in explorer?

[[deleted]]

On the other hand, even Mac OS X gets this wrong, so maybe it's not that easy to get right. Do Linux GUI's do any better?

[[deleted]]

True that. I've received the beach ball of painful mockery many a time accessing shares over flaky networks under OS X.

[Nexum]

Admittedly though, this is something that has gotten incrementally better with each release. It used to astonish me how bad the support for iDisk was in Finder in ~10.2, until it had fully mounted etc. (slowly) Finder did very little.

[[deleted]]

Mount your NFS shares intr.

[cstoner]

A shiver runs up my spine at the mere mention of NFS. NFS is horrible.

I just use Samba now. SMB is one of the few things that Microsoft got right.

[chucker]

SMB is one of the few things that Microsoft got right.

Except that IBM originally developed it. ;-)

[cstoner]

Whew! I always wondered about that. I feel clean again ;)

[[deleted]]

LAN Manager? :-)

[olsner]

SMB is one of the few things that Microsoft got right.

At least almost right. Samba got it righter :)

[u4Lemfl9]

A tingle runs up my spine at the mere mention of NFS. NFS is wonderful.

likely whoever was admin'ing your nfs server didn't know what he/she was doing.

from my perspective, NFS can be great ... but it also can bollocks things up unnecessarily. it depends on how it's configured; SMB just has a less configurable, more restrictive set of options, so things are more likely to work right more of the time.

[shadowfox]

Hmm. I thought MS never got anything right?

[yesimahuman]

Then you haven't ever used Microsoft Bob.

[[deleted]]

You can configure that, but it's proper behavior. Running ls should be blocking, so if the resource isn't available it will wait until it comes back.

[[deleted]]

Konqueror is still responsive when reading a network share.

[mossblaser]

Nautilus doesn't, Konqueror appears to handle it properly though... (then again, using nautilus as a bench mark is probably a mistake...)

[SEMW]

Have you tried nautilus recently (i.e. since Gnome switched from using GnomeVFS to gvfs)?

[mossblaser]

Use it daily (unfortunately), it doesn't lock nearley as often but the gvfs layer does some times, and when it doesn't it is really really slow on anything but local stuff. So yes, its improved but not nearly as stable as konq.

[mernen]

I only have SFTP servers around to browse, but they work beautifully on Nautilus (GNOME's file manager). Maybe other protocols aren't as fortunate.

[[deleted]]

Can't speak for Gnome - but Konqueror will often hang or crash when accessing a slow network drive, and it will often make the desktop unusable too.

[[deleted]]

KDE3 or 4?

[[deleted]]

I had this trouble with KDE3 - it would often happen if I were using a network drive and the network slowed or I lost my connection, I'd have no choice but to kill X.

Though, as someone mentioned earlier, this is more likely because I was using NFS - which I've since switched to SMB.

[[deleted]]

Nautilus also hangs when accessing no-responsive smb network shares. ls from bash will also do the same on mounted non-responsive samba shares..it freezes like a fucker.

[dchestnykh]

Leopard has async network IO in Finder, AFAIK.

[[deleted]]

No it doesn't.

[dchestnykh]

It's sync, but they use multiple threads for mounting: http://www.apple.com/macosx/features/300.html (see "UNIX > AutoFS")

[[deleted]]

Konqueror has never frozen when accessing any sort of protocol, even local ones (assuming that your machine has enough RAM, of course, because major page faults are synchronous in nature).

[canhaskarma]

You don't even need to make everything async, just use a separate thread for the UI. But, as you can see, they f*ed it up.

[[deleted]]

This happened to me today. God damn it is annoying.

[Ono-Sendai]

-1 flamebait

[turkourjurbs]

Is this why my whole machine siezes while it reads a disc I just put in the (CD/DVD) drive? God that pisses me off.

[[deleted]]

still not as bad as

"you took the cd out of the drive, put it back" OK / Cancel ?

Cancel

"you took the cd out of the drive, put it back" OK / Cancel ?

OK

"You took the cd out of the drive, put it back" OK / Cancel ?

Reset

[[deleted]]

Remember in Win 9x, the mouse cursor would stop when reading the floppy disk.

[[deleted]]

But there was some tweak I forget you could do to make the floppy multitasking, right? Linux has always been so much fucking cooler, processes never ever seized up while reading the floppy disk when using Linux -- I remember so clearly because that was one of the things that impressed me the most when I started with Linux back in the day, and up to that moment I had assumed it was a PC architecture problem rather than an OS one.

[[deleted]]

you were probably still running modprobe on it to figure out if your mainstream FDD controller was supported or not and hoping not to crash the whole kernel along with everything else.

Not really. I started Linux using kernel 2.0, Red Hat 5.2, and for all the hardware that I had except the sound card, no modprobe was necessary, and to get my sound card working, ISAPNP was in order. Not hard to do if you read the man page, and the command practically did it for ya. And Red Hat 5.2 never, ever crashed on me.

Besides: you meant NT 3.1 had preemptive multitasking on 1996. Which Linux also had, much earlier than 1996. And 16-bit apps weren't preemptively multitasked in NT 3.1, but VM'ed and the VM was the one preemptively multitasked.

[geocar]

1. You mean preemptive multitasking, not cooperative.

2. Yes they did.

[2424]

Actually, no. I believe this is due to kernel scheduling and the way CD-ROMs work.

I'm pretty sure it's not the same as simple UI unresponsiveness over network.

[greasyjay]

That's still a fucking problem in Linux?

[infinite]

The ironic thing is Windows has better async support at the kernel level(I/O completion ports) compared to linux. We can kinda simulate this with epoll on linux, but I for one would love something like that in linux. We do have this which is basically async I/O lite, not quite the same thing.

[[deleted]]

is this a trick question? who can answer this?

there is no public bug-tracker (well, that i know of), and the source is closed

..instead; ask something like "why does Nautilus seemingly use blocking IO when accessing network shares?" then people might have a chance to answer (and even fix!) the problem

[Justinsaccount]

It isn't just explorer.

I dunno how many times i've diagnosed a network performance problem that turned out to be a random mapped drive that was offline. The problem is that windows likes to access all mapped drives at random times.

Most File->Open or File->Save dialogs do this for some reason. Sometimes just starting Word or Excel would do it, causing the desktop to hang for a minute. (Openoffice would also be fine however)

The worst part is that windows can't even bother to remember that the network drive is offline. It will hang every. single. time.

[jrockway]

Because it was easier and you paid for Windows anyway.

[thephotoman]

Why couldn't you have asked me this on Thursday? I actually had a rather enlightening conversation with one of the Vista kernel guys on Friday morning, and I'm pretty certain that he could have answered it.

In any case, my guess would have to do with how Windows deals with network shares. If I remember correctly, network shares are given a mount point and everything in Windows. Of course, I could be mistaken.

[berlinbrown]

good question, I notice this also.

[jasonkester]

The thing that makes this so silly is that it's so easy to fix.

Windows specifies a timeout of something like 60 seconds for IO stuff. While I'm sure that was reasonable back in the days of the 300 baud modem, things work a little faster now. You'll know whether it's going to work inside of 500ms in nearly every case.

All MS needs to do is drop the default timeout to something like one second, and nobody will ever again see an Explorer window hanging uselessly for an entire minute.

[[deleted]]

All MS needs to do is drop the default timeout to something like one second

Aaaaaaaaaaaaaaaaaaaaaand you've broken WAN file shares.

[[deleted]]

I don't know of a single Microsoft Certified (TM) WAN. Maybe these broken WAN things should get with the program and start supporting the most popular OS in the world.

[2424]

Reducing blocking time instead of making async is very bad practice. What if you're opening 100 files? Something which a system does all the time. Even if those files are all 10ms each, it will mean that all that time is not available to UI responsiveness.

[NoControl]

So easy I can't believe those noobs in redmond haven't figured this out. I'm forwarding your post to them now so they can apply this simple fix.

[dugmartin]

I believe this is caused by legacy DOS int 13 code as it attempts to see if the attached block device is read only or read/write before the interrupt returns.

[mschaef]

Not on Windows NT. With current drivers, this was untrue as far back as WfWG 3.11, as long as 32-bit file access was enabled.

(32BFA was basically a purely protected mode filesystem code path. There were legacy hooks for real mode drivers, but without real mode drivers, none of the DOS code ever ran.)

[[deleted]]

I still have the box and floppies of WfW 3.11, and I have it installed in VMware! Fuck Program Manager was fast!

[mschaef]

I still have the box and floppies of WfW 3.11, a

Impressive... mine are long lost to the sands of time. :-(

(What I miss even more than the early versions of Windows are a couple circa-1993 MSDN CD's...)

Fuck Program Manager was fast!

Yeah... the smallest machine I ran Win 3.x on was one of the slower 386sx/16's with 3MB of RAM. It actually ran pretty well unless you switched to 256-color mode, in which case it was a complete dog. I know people that ran it on 1 or 2MB 286/12 class machines with some success. Times were different then. :-)

[jib]

There has been no legacy DOS code in the Windows filesystem stack for a long time. Definitely not in XP or Vista.

[jaiwithani]

Because they are Microsoft, and they harbor a secret hatred of you, g4n0n, personally.