在solr的查询请求中添加timeAllowed参数，可以限定solr查询的请求时间，在solr内部，是通过TimeLimitingCollector类来实现该功能的
在org.apache.solr.handler.component.QueryComponent类中的process方法中处理该参数
代码语言：javascript复制// -1 as flag if not set.
// 从请求中获取timeAllowed参数，默认值是-1
long timeAllowed = params.getLong(CommonParams.TIME_ALLOWED, -1L);
if (null != rb.getCursorMark() && 0 < timeAllowed) {
// fundamentally incompatible
throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "Can not search using both "
CursorMarkParams.CURSOR_MARK_PARAM " and " CommonParams.TIME_ALLOWED);
}
QueryCommand cmd = rb.createQueryCommand();
// 设置solr的query请求的超时时间
cmd.setTimeAllowed(timeAllowed);在org.apache.solr.search.SolrIndexSearcher类中getDocListNC方法中，通过调用buildAndRunCollectorChain方法，来生成TimeLimitingCollector类
代码语言：javascript复制// 获取请求中query的请求超时时间
final long timeAllowed = cmd.getTimeAllowed();
// 如果请求中设置的超时时间大于0， 生成TimeLimitingCollector
if (timeAllowed > 0) {
collector = new TimeLimitingCollector(collector, TimeLimitingCollector.getGlobalCounter(), timeAllowed);
}最终通过调用org.apache.lucene.search.IndexSearcher类中的public void search(Query query, Collector results)方法来起作用
在org.apache.lucene.search.IndexSearcher类中，lucene请求的源码如下
代码语言：javascript复制protected void search(List<LeafReaderContext> leaves, Weight weight, Collector collector)
throws IOException {
// TODO: should we make this
// threaded...? the Collector could be sync'd?
// always use single thread:
for (LeafReaderContext ctx : leaves) { // search each subreader
final LeafCollector leafCollector;
try {
// 如果是第一个segment的reader, 则通过调用setBaseline()方法来设置请求的最终执行结束时间
leafCollector = collector.getLeafCollector(ctx);
} catch (CollectionTerminatedException e) {
// there is no doc of interest in this reader context
// continue with the following leaf
continue;
}
// 生成BulkScorer对象
BulkScorer scorer = weight.bulkScorer(ctx);
if (scorer != null) {
try {
// 对query查询相关的文档进行打分
scorer.score(leafCollector, ctx.reader().getLiveDocs());
} catch (CollectionTerminatedException e) {
// collection was terminated prematurely
// continue with the following leaf
}
}
}
}org.apache.lucene.search.Weight.DefaultBulkScorer中对每一个找到的docId进行评分
代码语言：javascript复制 /** Specialized method to bulk-score all hits; we
* separate this from {@link #scoreRange} to help out
* hotspot.
* See <a href="https://issues.apache.org/jira/browse/LUCENE-5487">LUCENE-5487</a> */
static void scoreAll(LeafCollector collector, DocIdSetIterator iterator, TwoPhaseIterator twoPhase, Bits acceptDocs) throws IOException {
if (twoPhase == null) {
// 遍历每一个找到的docId
for (int doc = iterator.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = iterator.nextDoc()) {
// 判断找到的docId是不是满足条件，是否被删除
if (acceptDocs == null || acceptDocs.get(doc)) {
// 调用collector的collect方法对每一个docId进行评分，该collector会在调用实际的
// collector之前判断请求是否超时，如果超时，则抛出
collector.collect(doc);
}
}
} else {
// The scorer has an approximation, so run the approximation first, then check acceptDocs, then confirm
final DocIdSetIterator approximation = twoPhase.approximation();
for (int doc = approximation.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = approximation.nextDoc()) {
if ((acceptDocs == null || acceptDocs.get(doc)) && twoPhase.matches()) {
collector.collect(doc);
}
}
}
}TimeLimitingCollector中collect方法对找到的每一个docId进行判断是否已经超过结束时间
代码语言：javascript复制 @Override
public LeafCollector getLeafCollector(LeafReaderContext context) throws IOException {
this.docBase = context.docBase;
if (Long.MIN_VALUE == t0) {
setBaseline();
}
final long time = clock.get();
if (time - timeout > 0L) {
throw new TimeExceededException(timeout - t0, time - t0, -1);
}
return new FilterLeafCollector(collector.getLeafCollector(context)) {
@Override
public void collect(int doc) throws IOException {
final long time = clock.get();
// 判断是否已经超过结束时间
if (time - timeout > 0L) {
if (greedy) {
//System.out.println(this " greedy: before failing, collecting doc: " (docBase doc) " " (time-t0));
in.collect(doc);
}
//System.out.println(this " failing on: " (docBase doc) " " (time-t0));
throw new TimeExceededException( timeout-t0, time-t0, docBase doc );
}
//System.out.println(this " collecting: " (docBase doc) " " (time-t0));
in.collect(doc);
}
};
}lucene中使用org.apache.lucene.search.TimeLimitingCollector.TimerThread类进行模拟时钟计时，可以参考这篇文章 http://pzemtsov.github.io/2017/07/23/the-slow-currenttimemillis.html 来了解lucene这样设计的原因。
