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// gcc cache2.c ../linux/shmem.o -o cache2
// Initial draft of my new cache system...
// includes some simulation code, using usleep() to emulate limited bandwith
// TODO: seeking, data consistency checking
#define READ_SPEED 20
#define FILL_SPEED 10
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "../linux/shmem.h"
typedef struct {
// constats:
void *buffer; // base pointer of the alllocated buffer memory
int buffer_size; // size of the alllocated buffer memory
int sector_size; // size of a single sector (2048/2324)
// Note: buffer_size should be N*sector_size, where N is integer...
int back_size; // we should keep back_size amount of old bytes for backward seek
int fill_limit; // we should fill buffer if space>fill_limit
// reader's pointers:
int read_filepos;
// filler's pointers:
int min_filepos; // buffer contain only a part of the file, from min-max pos
int max_filepos;
int offset; // filepos <-> bufferpos offset value (filepos of the buffer's first byte)
// commands/locking:
int cmd_lock; // 1 if we will seek/reset buffer, 2 if we are ready for cmd
int fifo_flag; // 1 if we should use FIFO to notice cache about buffer reads.
} cache_vars_t;
int min_fill=0;
int sleep_flag=0;
void cache_stats(cache_vars_t* s){
int newb=s->max_filepos-s->read_filepos; // new bytes in the buffer
printf("0x%06X [0x%06X] 0x%06X ",s->min_filepos,s->read_filepos,s->max_filepos);
printf("%3d %% (%3d%%)\n",100*newb/s->buffer_size,100*min_fill/s->buffer_size);
}
int cache_read(cache_vars_t* s,int size){
int total=0;
while(size>0){
int pos,newb,len;
pos=s->read_filepos - s->offset;
if(pos<0) pos+=s->buffer_size; else
if(pos>=s->buffer_size) pos-=s->buffer_size;
newb=s->max_filepos-s->read_filepos; // new bytes in the buffer
if(newb<min_fill) min_fill=newb; // statistics...
if(newb<=0){
// waiting for buffer fill...
usleep(10000); // 10ms
continue;
}
// printf("*** newb: %d bytes ***\n",newb);
if(newb>s->buffer_size-pos) newb=s->buffer_size-pos; // handle wrap...
if(newb>size) newb=size;
// len=write(mem,newb)
printf("Buffer read: %d bytes\n",newb);
len=newb;usleep(len*READ_SPEED*sleep_flag);
// ...
s->read_filepos+=len;
size-=len;
total+=len;
}
return total;
}
int cache_fill(cache_vars_t* s){
int read,back,newb,space,len,pos,endpos;
read=s->read_filepos;
// calc number of back-bytes:
back=read - s->min_filepos;
if(back<0) back=0; // strange...
if(back>s->back_size) back=s->back_size;
// calc number of new bytes:
newb=s->max_filepos - read;
if(newb<0) newb=0; // strange...
// calc free buffer space:
space=s->buffer_size - (newb+back);
// calc bufferpos:
pos=s->max_filepos - s->offset;
if(pos>=s->buffer_size) pos-=s->buffer_size; // wrap-around
if(space<s->fill_limit){
// printf("Buffer is full (%d bytes free, limit: %d)\n",space,s->fill_limit);
return 0; // no fill...
}
// printf("### read=0x%X back=%d newb=%d space=%d pos=%d\n",read,back,newb,space,pos);
// reduce space if needed:
if(space>s->buffer_size-pos) space=s->buffer_size-pos;
if(space>32768) space=32768; // limit one-time block size
s->min_filepos=read-back; // avoid seeking-back to temp area...
// ....
printf("Buffer fill: %d bytes of %d\n",space,s->buffer_size);
len=space; usleep(len*FILL_SPEED*sleep_flag);
// ....
s->max_filepos+=len;
if(pos+len>=s->buffer_size){
// wrap...
s->offset+=s->buffer_size;
}
return len;
}
cache_vars_t* cache_init(int size,int sector){
int num;
cache_vars_t* s=shmem_alloc(sizeof(cache_vars_t));
memset(s,0,sizeof(cache_vars_t));
num=size/sector;
s->buffer_size=num*sector;
s->sector_size=sector;
s->buffer=shmem_alloc(s->buffer_size);
s->fill_limit=8*sector;
s->back_size=size/2;
return s;
}
int main(){
cache_vars_t* s=cache_init(1024*1024,2048);
// while(cache_fill(s)){ } // fill buffer:
min_fill=s->buffer_size;
sleep_flag=1; // start simulation
if(fork()){
while(1){
if(!cache_fill(s)) usleep(10000); // wait 10ms for buffer space
//cache_stats(s);
}
} else {
srand(12345);
while(1){
int len=10+rand()&8191;
cache_stats(s);
cache_read(s,len);
}
}
}
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