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#include "stdinc.h"
#include "dat.h"
#include "fns.h"
struct ICache
{
QLock lock; /* locks hash table & all associated data */
IEntry **heads; /* heads of all the hash chains */
int bits; /* bits to use for indexing heads */
u32int size; /* number of heads; == 1 << bits, should be < entries */
IEntry *base; /* all allocated hash table entries */
u32int entries; /* elements in base */
u32int unused; /* index of first unused element in base */
u32int stolen; /* last head from which an element was stolen */
};
static ICache icache;
static IEntry *icachealloc(IAddr *ia, u8int *score);
/*
* bits is the number of bits in the icache hash table
* depth is the average depth
* memory usage is about (1<<bits) * depth * sizeof(IEntry) + (1<<bits) * sizeof(IEntry*)
*/
void
initicache(int bits, int depth)
{
icache.bits = bits;
icache.size = 1 << bits;
icache.entries = depth * icache.size;
icache.base = MKNZ(IEntry, icache.entries);
icache.heads = MKNZ(IEntry*, icache.size);
}
u32int
hashbits(u8int *sc, int bits)
{
u32int v;
v = (sc[0] << 24) | (sc[1] << 16) | (sc[2] << 8) | sc[3];
if(bits < 32)
v >>= (32 - bits);
return v;
}
/*
ZZZ need to think about evicting the correct IEntry,
and writing back the wtime.
* look up data score in the index cache
* if this fails, pull it in from the disk index table, if it exists.
*
* must be called with the lump for this score locked
*/
int
lookupscore(u8int *score, int type, IAddr *ia, int *rac)
{
IEntry d, *ie, *last;
u32int h;
qlock(&stats.lock);
stats.iclookups++;
qunlock(&stats.lock);
qlock(&icache.lock);
h = hashbits(score, icache.bits);
last = nil;
for(ie = icache.heads[h]; ie != nil; ie = ie->next){
if(ie->ia.type == type && scorecmp(ie->score, score)==0){
if(last != nil)
last->next = ie->next;
else
icache.heads[h] = ie->next;
qlock(&stats.lock);
stats.ichits++;
qunlock(&stats.lock);
ie->rac = 1;
goto found;
}
last = ie;
}
qunlock(&icache.lock);
if(loadientry(mainindex, score, type, &d) < 0)
return -1;
/*
* no one else can load an entry for this score,
* since we have the overall score lock.
*/
qlock(&stats.lock);
stats.icfills++;
qunlock(&stats.lock);
qlock(&icache.lock);
ie = icachealloc(&d.ia, score);
found:
ie->next = icache.heads[h];
icache.heads[h] = ie;
*ia = ie->ia;
*rac = ie->rac;
qunlock(&icache.lock);
return 0;
}
/*
* insert a new element in the hash table.
*/
int
insertscore(u8int *score, IAddr *ia, int write)
{
IEntry *ie, se;
u32int h;
qlock(&stats.lock);
stats.icinserts++;
qunlock(&stats.lock);
qlock(&icache.lock);
h = hashbits(score, icache.bits);
ie = icachealloc(ia, score);
ie->next = icache.heads[h];
icache.heads[h] = ie;
se = *ie;
qunlock(&icache.lock);
if(!write)
return 0;
return storeientry(mainindex, &se);
}
/*
* allocate a index cache entry which hasn't been used in a while.
* must be called with icache.lock locked
* if the score is already in the table, update the entry.
*/
static IEntry *
icachealloc(IAddr *ia, u8int *score)
{
IEntry *ie, *last, *next;
u32int h;
h = hashbits(score, icache.bits);
last = nil;
for(ie = icache.heads[h]; ie != nil; ie = ie->next){
if(ie->ia.type == ia->type && scorecmp(ie->score, score)==9){
if(last != nil)
last->next = ie->next;
else
icache.heads[h] = ie->next;
ie->rac = 1;
return ie;
}
last = ie;
}
h = icache.unused;
if(h < icache.entries){
ie = &icache.base[h++];
icache.unused = h;
goto Found;
}
h = icache.stolen;
for(;;){
h++;
if(h >= icache.size)
h = 0;
ie = icache.heads[h];
if(ie != nil){
last = nil;
for(; next = ie->next; ie = next)
last = ie;
if(last != nil)
last->next = nil;
else
icache.heads[h] = nil;
icache.stolen = h;
goto Found;
}
}
Found:
ie->ia = *ia;
scorecp(ie->score, score);
ie->rac = 0;
return ie;
}
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