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tal/link
link helper for tal
Rusty Russell <rusty@rustcorp.com.au>
Tal does not support talloc-style references. In the cases where an object needs multiple parents, all parents need to be aware of the situation; thus tal/link is a helper where all "parents" tal_link an object they agree to share ownership of.
// Silly program which keeps a cache of uppercased strings.
// The cache wants to keep strings around even after they may have
// been "freed" by the caller.
// Given 'hello' outputs '1 cache hits HELLO '
// Given 'hello hello there' outputs '4 cache hits HELLO HELLO THERE '
#include <stdio.h>
#include <err.h>
#include <string.h>
#include <ctype.h>
#include <ccan/tal/link/link.h>
#include <ccan/tal/str/str.h>
struct upcache {
const char *str;
const char *upstr;
};
static struct upcache *cache;
static unsigned int cache_hits = 0;
#define CACHE_SIZE 4
static void init_upcase(void)
{
cache = tal_arrz(NULL, struct upcache, CACHE_SIZE);
}
static struct upcache *lookup_upcase(const char *str)
{
unsigned int i;
for (i = 0; i < CACHE_SIZE; i++)
if (cache[i].str && !strcmp(cache[i].str, str)) {
cache_hits++;
return &cache[i];
}
return NULL;
}
static struct upcache *new_upcase(const char *str)
{
unsigned int i;
char *upstr;
upstr = tal_linkable(tal_strdup(NULL, str));
i = random() % CACHE_SIZE;
// Throw out old: works fine if cache[i].upstr is NULL.
tal_delink(cache, cache[i].upstr);
// Replace with new.
cache[i].str = str;
cache[i].upstr = tal_link(cache, upstr);
while (*upstr) {
*upstr = toupper(*upstr);
upstr++;
}
return &cache[i];
}
// If you want to keep the result, tal_link it.
static const char *get_upcase(const char *str)
{
struct upcache *uc = lookup_upcase(str);
if (!uc)
uc = new_upcase(str);
if (!uc)
return NULL;
return uc->upstr;
}
static void exit_upcase(void)
{
tal_free(cache);
printf("%u cache hits ", cache_hits);
}
int main(int argc, char *argv[])
{
unsigned int i;
const char **values;
// Initialize cache.
init_upcase();
// Throw values in.
values = tal_arr(NULL, const char *, argc);
for (i = 1; i < argc; i++)
values[i-1] = tal_link(values, get_upcase(argv[i]));
// This will free all the values, but cache will still work.
tal_free(values);
// Repeat!
values = tal_arr(NULL, const char *, argc);
for (i = 1; i < argc; i++)
values[i-1] = tal_link(values, get_upcase(argv[i]));
// This will remove cache links, but we still have a link.
exit_upcase();
// Show values, so we output something.
for (i = 0; i < argc - 1; i++)
printf("%s ", values[i]);
printf("\n");
// This will finally free the upcase strings (last link).
tal_free(values);
return 0;
}
BSD-MIT