使用php实现一致性hash算法

     hasher = isset($hasher) ? $hasher : new Crc32Hasher();        isset($replicas) && $this->replicas = $replicas;    }    public function addTarget($target, $weight = 1) {        $positions = array();        $existPositions = array_keys($this->positionTargetMap);        for ($i = 0; $i < $this->replicas * $weight; $i++) {            //find an position not in exist positions            $suffix = '';            do {                $suffix .= $i;                $position = $this->hasher->hash($target.''.$suffix);            } while (in_array($position, $existPositions));            //record position's target            $this->positionTargetMap[$position] = $target;            //collect position            $positions[] = $position;        }        //sort position        ksort($this->positionTargetMap);        //record target's positions        $this->targetPositionsMap[$target] = $positions;    }    public function removeTarget($target) {        if (!isset($this->targetPositionsMap[$target])) {            throw new Exception('remove not exists target: '.$target);        }        $positions = $this->targetPositionsMap[$target];        //remove target's positions        unset($this->targetPositionsMap[$target]);        //remove position's target        foreach ($positions as $position) {            unset($this->positionTargetMap[$position]);        }    }    public function lookup($resource) {        return $this->lookupList($resource, 1)[0];    }    public function lookupList($resource, $count) {        if ($this->isTargetsEmpty()) {            throw new Exception('lookup targets empty');        }        if ($count > count($this->targetPositionsMap)) {            throw new Exception('lookup targets not enough');        }        $targetList = array();        $hash = $this->hasher->hash($resource);        //find in the above positions        foreach ($this->positionTargetMap as $position => $t) {            if (count($targetList) == $count) {                break;            }            if ($hash >= $position) {                $targetList[] = $t;            }        }        //find in the below positions        if (count($targetList) < $count) {            foreach ($this->positionTargetMap as $position => $t) {                if (count($targetList) == $count) {                    break;                }                $targetList[] = $t;            }        }        return $targetList;    }    public function isTargetsEmpty() {        return count($this->targetPositionsMap) == 0;    }    public function addTargets($targets) {        foreach ($targets as $target) {            $this->addTarget($target);        }    }    public function removeTargets($targets) {        foreach ($targets as $target) {            $this->removeTarget($target);        }    }}