Re: [fpc-pascal] Better random numbers ?
On Friday 03 March 2006 12:55, Vincent Snijders wrote: > Jonas Maebe wrote: > > On 3 mrt 2006, at 13:42, Vinzent Hoefler wrote: > >>> BTW, I never would have guessed that the random number generator > >>> would have used threadvars. I would have thought, that on app > >>> start you would set one randseed and then call random from all > >>> threads. > >> > >> Considering that the state array for the Mersenne Twister is an > >> unprotected global variable, calling random from different threads > >> looks like a bad idea to me. > >> > >> I mean, it surely gives you sort of random values, but ... > > > > That's why its state (and indeed not just randseed) should be > > threadvars. > > Or use some locking mechanism. That would be slower, but would safe > some memory. I'd suggest both. :) Objectify the whole Mersenne Twister into a single "class", so that each thread can have it's own PRNG if necessary and provide a single global, but locked instance of it for the System.Random subroutines. Vinzent. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
Jonas Maebe wrote: On 3 mrt 2006, at 13:42, Vinzent Hoefler wrote: BTW, I never would have guessed that the random number generator would have used threadvars. I would have thought, that on app start you would set one randseed and then call random from all threads. Considering that the state array for the Mersenne Twister is an unprotected global variable, calling random from different threads looks like a bad idea to me. I mean, it surely gives you sort of random values, but ... That's why its state (and indeed not just randseed) should be threadvars. Or use some locking mechanism. That would be slower, but would safe some memory. Vincent ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
On 3 mrt 2006, at 13:42, Vinzent Hoefler wrote: BTW, I never would have guessed that the random number generator would have used threadvars. I would have thought, that on app start you would set one randseed and then call random from all threads. Considering that the state array for the Mersenne Twister is an unprotected global variable, calling random from different threads looks like a bad idea to me. I mean, it surely gives you sort of random values, but ... That's why its state (and indeed not just randseed) should be threadvars. Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
On Monday 27 February 2006 08:41, Vincent Snijders wrote: > BTW, I never would have guessed that the random number generator > would have used threadvars. I would have thought, that on app start > you would set one randseed and then call random from all threads. Considering that the state array for the Mersenne Twister is an unprotected global variable, calling random from different threads looks like a bad idea to me. I mean, it surely gives you sort of random values, but ... Vinzent. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
On 27 feb 2006, at 09:41, Vincent Snijders wrote: Some other workaround that comes to my mind is to do something like Randomize; RandSeed := RandSeed * getpid; This worked, cut the initial generation time from about 30 seconds down to under 1, of course right now it's NOT platform independent at all so I will need to enhance it but I like the direction of your thinking, combining randseed with some virtually guaranteed unique value solves the problem. Maybe you use a global variable and just add one for each randseed call. After all the only thing that matters for the randseed, is that it is different. BTW, I never would have guessed that the random number generator would have used threadvars. It doesn't currently. I would have thought, that on app start you would set one randseed and then call random from all threads. Every time you call random, the current randseed is read, some calculations are performed and a new value is stored in the randseed variable. So if two threads call random "at the same time", then both will use the same randseed value and thus return the same random value (in the -current- case that randseed is not a threadvar). Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
A.J. Venter wrote: Some other workaround that comes to my mind is to do something like Randomize; RandSeed := RandSeed * getpid; This worked, cut the initial generation time from about 30 seconds down to under 1, of course right now it's NOT platform independent at all so I will need to enhance it but I like the direction of your thinking, combining randseed with some virtually guaranteed unique value solves the problem. Maybe you use a global variable and just add one for each randseed call. After all the only thing that matters for the randseed, is that it is different. BTW, I never would have guessed that the random number generator would have used threadvars. I would have thought, that on app start you would set one randseed and then call random from all threads. Vincent. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
On 27 feb 2006, at 00:15, A.J. Venter wrote: Randomize; RandSeed := RandSeed * getpid; This worked, cut the initial generation time from about 30 seconds down to under 1, of course right now it's NOT platform independent at all so I will need to enhance it but I like the direction of your thinking, combining randseed with some virtually guaranteed unique value solves the problem. It's not just that, but randseed is not a threadvar. This means that all your threads use the same randseed variable, so if two threads call "random" at the same time they will still get the same "random" number. Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
On 27 Feb 06, at 1:15, A.J. Venter wrote: > > Some other workaround that comes to my mind is to do something like > >Randomize; > >RandSeed := RandSeed * getpid; > This worked, cut the initial generation time from about 30 seconds down to > under 1, of course right now it's NOT platform independent at all so I will > need to enhance it but I like the direction of your thinking, combining > randseed with some virtually guaranteed unique value solves the problem. System.GetProcessID should be perfectly platform independent. HTH Tomas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
> Some other workaround that comes to my mind is to do something like >Randomize; >RandSeed := RandSeed * getpid; This worked, cut the initial generation time from about 30 seconds down to under 1, of course right now it's NOT platform independent at all so I will need to enhance it but I like the direction of your thinking, combining randseed with some virtually guaranteed unique value solves the problem. Ciao A.J. -- A.J. Venter Chief Software Architect OpenLab International www.getopenlab.com www.silentcoder.co.za +27 82 726 5103 ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
> Hi, I am using standard run of the mill randomize/random() calls in a program > to generate random numbers, used in turn to select random data which is fed > into another program. You are just supposed to call randomize once, to initialize the random number generator. You then call random over and over, and a different random number gets generated from each successive call. The random call modifies the stored seed so that repeated calls give different answers. I can see how this might not work so well when you are calling the program over and over again (i.e., restarting it). One option is to have the random # generator program generate a large batch of numbers that are saved to a file, and you only call it again when the calling program has used up that batch. (If you are working in windows, you might look at the randgen program, freely available at http://www.winsite.com/bin/Info?1700036826 which can be used like this.) Another option is to have the random # generator program return its new seed value as well as its random number. When you call it again, you pass it the seed value that it last returned, and the random # generator program sets the seed to that value without calling randomize again. I hope something here useful to you... Jeff [EMAIL PROTECTED] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Better random numbers ?
A.J. Venter wrote: Hi, I am using standard run of the mill randomize/random() calls in a program to generate random numbers, used in turn to select random data which is fed into another program. (All this just to create a multi-language enabled module structure eh) Well there is just one little problem, on the commandline it works fine, just about every single call gives a different result, or different enough. But when run from inside my other app (where it is threaded) and where I cannot proceed until I have at least the first 5 non-repeating values, it doesn't work so great, I have to call the program an average of 40 times before the value changes - I presume because randomize gets it's seed from the clock and that is how long it takes for the whichever value it uses to update. So is there a better way I can do this ? Some way of getting a more frequently updated random seed ? I am talking literally every few milliseconds here. I think that this problem is more-or-less unavoidable when you want to really call Randomize/Random inside the program that is called very often. The proper solution is to use some system-wide generator, that doesn't have to be initialized every time you initialize your program. On Unix, just read /dev/urandom, this should return pseudo-random numbers. On Windows I guess that you will have to do something like that on your own (e.g. write a program in FPC that runs as a service and can be queried for random numbers). (Or you can use Cygwin routines to read Cygwin's /dev/urandom --- never done it, but it should be possible). Some other workaround that comes to my mind is to do something like Randomize; RandSeed := RandSeed * getpid; This way you increase chances that your RandSeed is different for different processes, since they will most probably get different (usually successive) pids. Probably there is some equivalent to "getpid" on Windows. Hope this helps. Michalis ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] Better random numbers ?
Hi, I am using standard run of the mill randomize/random() calls in a program to generate random numbers, used in turn to select random data which is fed into another program. (All this just to create a multi-language enabled module structure eh) Well there is just one little problem, on the commandline it works fine, just about every single call gives a different result, or different enough. But when run from inside my other app (where it is threaded) and where I cannot proceed until I have at least the first 5 non-repeating values, it doesn't work so great, I have to call the program an average of 40 times before the value changes - I presume because randomize gets it's seed from the clock and that is how long it takes for the whichever value it uses to update. So is there a better way I can do this ? Some way of getting a more frequently updated random seed ? I am talking literally every few milliseconds here. -- A.J. Venter Chief Software Architect OpenLab International www.getopenlab.com www.silentcoder.co.za +27 82 726 5103 ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
