Linked by Thom Holwerda on Sat 28th Jun 2008 22:09 UTC, submitted by diegocg
X11, Window Managers "Maybe I'm just naive, but designing a graphics API such that all image data had to be sent over a socket to another process every time the image needed to be drawn seems like complete idiocy. Unfortunately, that is precisely what the X Window System forces a program to do, and exactly what Cairo does when drawing images in Linux - a full copy of the image data, send to another process, no less, every time it is drawn. One would think there would be some room for improvement. Unsurprisingly, others felt the same way about X, and decided to write an extension, Xlib Shm or XShm for short, that allows images to placed in a shared memory segment from which the X server reads which allows the program to avoid the memory copy. GTK already makes use of the XShm extension, and it seems like a good idea to see if Gecko couldn't do the same."
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RE[2]: Exaggerating
by diegocg on Sun 29th Jun 2008 09:02 UTC in reply to "RE: Exaggerating"
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There's an additional big problem with sockets: Once you send the image to the server, the client can't "share" it, because it's living in the server's address space. So you have a copy of the image on the server AND exactly the same copy of the image on the client. The image is effectively using 2x its size in the memory.

The "right fix" for this stupid waste of resources is to free() the image on the client. With shared memory, you can SHARE the image's memory between the client and the process.

That's how things should work on a sane local graphic setup, but X is far from being "sane". Yes, IS efficient and comparable to other systems, but only because people have spent a lot of time workarounding the stupid things it does so that at the end in local systems it works like other sane systems.

That's the funny thing: X is supposed to be "network transparent", but then the server and the client need to DETECT if they're in "local mode", or if such extension is enabled or not, and make SPECIAL MODIFICATIONS to the code paths so that it works right. There's no "transparency" anymore, as applications (toolkits) need to be aware of such low-level graphic details and code different paths according to the results. It has been needed to create many X extensions, it has been needed to MODIFY applications to use those extensions...oh my god, it's just not fun even to think about it. And to think that backwards compatibility is all that was stopping people from doing it right...

Edited 2008-06-29 09:20 UTC

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