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• Does Mac OS X throttle the RATE of socket creation?

  - by pbhogan

  This may seem programming related, but this is an OS question. I'm writing a small high performance daemon that takes thousands of connections per second. It's working fine on Linux (specifically Ubuntu 9.10 on EC2). On Mac OS X if I throw a few thousand connections at it (roughly about 16350) in a benchmark that simply opens a connection, does it's thing and closes the connection, then the benchmark program hangs for several seconds waiting for a socket to become available before continuing (or timing out in the process). I used both Apache Bench as well as Siege (to make sure it wasn't the benchmark application). So why/how is Mac OS X limiting the RATE at which sockets can be used, and can I stop it from doing this? Or is there something else going on? I know there is a file descriptor limit, but I'm not hitting that. There is no error on accepting a socket, it's simply hangs for a while after the first (roughly) 16000, waiting -- I assume -- for the OS to release a socket. This shouldn't happen since all prior the sockets are closed at that point. They're supposed to come available at the rate they're closed, and do on Ubuntu, but there seems to be some kind of multi (5-10?) second delay on Mac OS X. I tried tweaking with ulimit every-which-way. Nada.

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• Does Mac OS X throttle the RATE of socket creation?

  - by pbhogan

  This may seem programming related, but this is an OS question. I'm writing a small high performance daemon that takes thousands of connections per second. It's working fine on Linux (specifically Ubuntu 9.10 on EC2). On Mac OS X if I throw a few thousand connections at it (roughly about 16350) in a benchmark that simply opens a connection, does it's thing and closes the connection, then the benchmark program hangs for several seconds waiting for a socket to become available before continuing (or timing out in the process). I used both Apache Bench as well as Siege (to make sure it wasn't the benchmark application). So why/how is Mac OS X limiting the RATE at which sockets can be used, and can I stop it from doing this? Or is there something else going on? I know there is a file descriptor limit, but I'm not hitting that. There is no error on accepting a socket, it's simply hangs for a while after the first (roughly) 16000, waiting -- I assume -- for the OS to release a socket. This shouldn't happen since all prior the sockets are closed at that point. They're supposed to come available at the rate they're closed, and do on Ubuntu, but there seems to be some kind of multi (5-10?) second delay on Mac OS X. I tried tweaking with ulimit every-which-way. Nada.

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• How do I do high quality scaling of a image?

  - by pbhogan

  I'm writing some code to scale a 32 bit RGBA image in C/C++. I have written a few attempts that have been somewhat successful, but they're slow and most importantly the quality of the sized image is not acceptable. I compared the same image scaled by OpenGL (i.e. my video card) and my routine and it's miles apart in quality. I've Google Code Searched, scoured source trees of anything I thought would shed some light (SDL, Allegro, wxWidgets, CxImage, GD, ImageMagick, etc.) but usually their code is either convoluted and scattered all over the place or riddled with assembler and little or no comments. I've also read multiple articles on Wikipedia and elsewhere, and I'm just not finding a clear explanation of what I need. I understand the basic concepts of interpolation and sampling, but I'm struggling to get the algorithm right. I do NOT want to rely on an external library for one routine and have to convert to their image format and back. Besides, I'd like to know how to do it myself anyway. :) I have seen a similar question asked on stack overflow before, but it wasn't really answered in this way, but I'm hoping there's someone out there who can help nudge me in the right direction. Maybe point me to some articles or pseudo code... anything to help me learn and do. Here's what I'm looking for: 1. No assembler (I'm writing very portable code for multiple processor types). 2. No dependencies on external libraries. 3. I am primarily concerned with scaling DOWN, but will also need to write a scale up routine later. 4. Quality of the result and clarity of the algorithm is most important (I can optimize it later). My routine essentially takes the following form: DrawScaled( uint32 *src, uint32 *dst, src_x, src_y, src_w, src_h, dst_x, dst_y, dst_w, dst_h ); Thanks! UPDATE: To clarify, I need something more advanced than a box resample for downscaling which blurs the image too much. I suspect what I want is some kind of bicubic (or other) filter that is somewhat the reverse to a bicubic upscaling algorithm (i.e. each destination pixel is computed from all contributing source pixels combined with a weighting algorithm that keeps things sharp. EXAMPLE: Here's an example of what I'm getting from the wxWidgets BoxResample algorithm vs. what I want on a 256x256 bitmap scaled to 55x55. And finally: the original 256x256 image

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• How to algorithmically partion a keyspace?

  - by pbhogan

  This is related to consistent hashing and while I conceptually understand what I need to do, I'm having a hard time translating this into code. I'm trying to divide a given keyspace (say, 128 bits) into equal sized partitions. I want the upper bound (highest key) of each partition. Basically, how would I complete this? #define KEYSPACE_BYTE_SIZE 16 #define KEYSPACE_BIT_SIZE (KEYSPACE_BYTE_SIZE * 8) typedef struct _key { char byte[KEYSPACE_BYTE_SIZE]; } key; key * partition_keyspace( int num_partitions ) { key * partitions = malloc( sizeof(key) * num_partitions ); // ... }

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