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/*
traversing a flat pre-built (in speed20.c) pointer list of 10 million records
of 5 fields in a 1 GB database using a ctrl record to scan
different segments of the list in parallel.
Nr of segments is built by speed20: control the number there.
Compile with
gcc speed21.c -o speed21 -O2 -lwgdb -lpthread
Ctrl record (see speed20.c) fields:
0: type (unused)
1: ptr field (3 here)
2: start pointer
3: midpointer0
4: midpointer1
...
N: ptr to last record
N+1: NULL
Database was created earlier by speed20 and is not freed here.
one thread:
real 0m0.110s
user 0m0.064s
sys 0m0.045s
two threads:
real 0m0.064s
user 0m0.071s
sys 0m0.048s
three threads:
real 0m0.047s
user 0m0.073s
sys 0m0.052s
four threads:
real 0m0.041s
user 0m0.072s
sys 0m0.057s
eight threads:
real 0m0.032s
user 0m0.097s
sys 0m0.062s
sixteen threads
real 0m0.033s
user 0m0.088s
sys 0m0.076s
*/
#include <whitedb/dbapi.h>
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#define RECORD_HEADER_GINTS 3
#define wg_field_addr(db,record,fieldnr) (((wg_int*)record)+RECORD_HEADER_GINTS+fieldnr)
#define MAX_THREADS 100
#define DB_NAME "20"
void *process(void *targ);
struct thread_data{
int thread_id; // 0,1,..
void* db; // db handler
wg_int fptr; // first pointer
wg_int lptr; // last pointer
int ptrfld; // pointer field in rec
int res; // stored by thread
};
int main(int argc, char **argv) {
void *db, *ctrl, *rec;
char *name=DB_NAME;
int i,ptrfld,ptrs,rc;
wg_int encptr,tmp,first,next,last;
pthread_t threads[MAX_THREADS];
struct thread_data tdata[MAX_THREADS];
pthread_attr_t attr;
long tid;
db = wg_attach_database(name, 1000000000);
if (!db) { printf("db creation failed \n"); exit(0); }
// get values from cntrl record
ctrl=wg_get_first_record(db);
ptrfld=wg_decode_int(db,wg_get_field(db,ctrl,1));
first=wg_get_field(db,ctrl,2);
for(ptrs=0;ptrs<10000;ptrs++) {
tmp=wg_get_field(db,ctrl,3+ptrs);
if ((int)tmp==0) break;
last=tmp;
}
printf("\nsegments found: %d \n",ptrs);
if (ptrs>=MAX_THREADS) {
printf("List segment nr larger than MAX_THREADS, exiting\n");
wg_detach_database(db);
pthread_exit(NULL);
return 0;
}
// prepare and create threads
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
for(tid=0;tid<ptrs;tid++) {
first=wg_get_field(db,ctrl,2+tid);
next=wg_get_field(db,ctrl,2+tid+1);
tdata[tid].thread_id=tid;
tdata[tid].db=db;
tdata[tid].fptr=first;
tdata[tid].lptr=next;
tdata[tid].ptrfld=ptrfld;
tdata[tid].res=0;
rc=pthread_create(&threads[tid], &attr, process, (void *) &tdata[tid]);
}
// wait for all threads to finish
for(tid=0;tid<ptrs;tid++) {
pthread_join(threads[tid],NULL);
//printf("thread %d finished with res %d\n",
// tdata[tid].thread_id,tdata[tid].res);
}
printf("\nall threads finished\n");
wg_detach_database(db);
pthread_exit(NULL);
return 0;
}
void *process(void *targ) {
struct thread_data *tdata;
void *db,*rec,*lptr;
wg_int encptr;
int i,tid,ptrfld;
tdata=(struct thread_data *) targ;
tid=tdata->thread_id;
db=tdata->db;
ptrfld=tdata->ptrfld;
rec=wg_decode_record(db,tdata->fptr);
lptr=wg_decode_record(db,tdata->lptr);
printf("thread %d starts, first el value %d \n",tid,
wg_decode_int(db,wg_get_field(db,rec,1)));
i=1;
while(1) {
encptr=*(wg_field_addr(db,rec,ptrfld)); // encptr is not yet decoded
rec=wg_decode_record(db,encptr); // get a pointer to the previous record
if (rec==lptr) break;
i++;
}
tdata->res=i;
printf ("thread %d finishing with res %d \n",tid,i);
pthread_exit((void*) tid);
}
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