得物 iOS 启动优化之 Building Closure

一

神秘的 BuildingClosure

dyld && BuildingClosure

BuildingClosure 非常耗时

BuildingClosure 文件解析

二

离奇的启动耗时暴增事件

启动耗时暴增 200ms

BuildingClosure 

耗时异常变化定位

三

启动优化新秘境

void PrebuiltObjC::generateHashTables(RuntimeState& state){    // Write out the class table    writeObjCDataStructHashTable(state, PrebuiltObjC::ObjCStructKind::classes, objcImages, classesHashTable, duplicateSharedCacheClassMap, classMap);    // Write out the protocol table    writeObjCDataStructHashTable(state, PrebuiltObjC::ObjCStructKind::protocols, objcImages, protocolsHashTable, duplicateSharedCacheClassMap, protocolMap);    // If we have closure selectors, we need to make a hash table for them.    if( !closureSelectorStrings.empty() ) {        objc::PerfectHash phash;        objc::PerfectHash::make_perfect(closureSelectorStrings, phash);        size_t size = ObjCStringTable::size(phash);        selectorsHashTable.resize(size);        //printf("Selector table size: %lld\n", size);        selectorStringTable = (ObjCStringTable*)selectorsHashTable.begin();        selectorStringTable->write(phash, closureSelectorMap.array());    }}

Perfect Hash

for (si=1; ; ++si)    {        ub4 rslinit;        /* Try to find distinct (A,B) for all keys */        *salt = si * 0x9e3779b97f4a7c13LL; /* golden ratio (arbitrary value) */        initnorm(keys, *alen, blen, smax, *salt);        rslinit = inittab(tabb, keys, FALSE);        if (rslinit == 0)        {            /* didn't find distinct (a,b) */            if (++bad_initkey >= RETRY_INITKEY)            {                /* Try to put more bits in (A,B) to make distinct (A,B) more likely */                if (*alen < maxalen)                {                    *alen *= 2;                }                else if (blen < smax)                {                    blen *= 2;                    tabb.resize(blen);                    tabq.resize(blen+1);                }                bad_initkey = 0;                bad_perfect = 0;            }            continue;                             /* two keys have same (a,b) pair */        }        /* Given distinct (A,B) for all keys, build a perfect hash */        if (!perfect(tabb, tabh, tabq, smax, scramble, (ub4)keys.count()))        {            if (++bad_perfect >= RETRY_PERFECT)            {                if (blen < smax)                {                    blen *= 2;                    tabb.resize(blen);                    tabq.resize(blen+1);                    --si;               /* we know this salt got distinct (A,B) */                }                else                {                    return false;                }                bad_perfect = 0;            }            continue;        }        break;    }

/* * put keys in tabb according to key->b_k * check if the initial hash might work */staticintinittab_ts(dyld3::OverflowSafeArray<bstuff>& tabb, dyld3::OverflowSafeArray<key>& keys, int complete, int si)// bstuff   *tabb;                     /* output, list of keys with b for (a,b) */// ub4       blen;                                            /* length of tabb */// key      *keys;                               /* list of keys already hashed */// int       complete;        /* TRUE means to complete init despite collisions */{  int  nocollision = TRUE;  ub4 i;  memset((void *)tabb.begin(), 0, (size_t)(sizeof(bstuff)*tabb.maxCount()));  /* Two keys with the same (a,b) guarantees a collision */  for (i = 0; i < keys.count(); i++) {    key *mykey = &keys[i];    key *otherkey;    for (otherkey=tabb[mykey->b_k].list_b;     otherkey;     otherkey=otherkey->nextb_k)    {      if (mykey->a_k == otherkey->a_k)      {          // 打印冲突的字符串        std::cout << mykey->name_k << " and " << otherkey->name_k << " has the same ak " << otherkey->a_k << " si is " << si << std::endl;        nocollision = FALSE;          /* 屏蔽此处代码，有冲突的情况下，继续执行，便于打印所有的冲突    if (!complete)      return FALSE;           */      }    }    ++tabb[mykey->b_k].listlen_b;    mykey->nextb_k = tabb[mykey->b_k].list_b;    tabb[mykey->b_k].list_b = mykey;  }  /* no two keys have the same (a,b) pair */  return nocollision;}

向前一步

四

总结