QNetworkAccessManager unable to close socket in time

In my APP, there are 50 QWebPages, which loading many URLs without stop, these QWebPages share one QNetworkAccessManager.

After about 300 URLs are loaded by QWebPages, my APP crashed and display following message:
[New Thread 0x5f585940 (LWP 28949)]
QEventDispatcherUNIXPrivate(): Unable to create thread pipe: Too many open files
QEventDispatcherUNIXPrivate(): Can not continue without a thread pipe

I have recorded every QNetworkReply created by QNetworkAccessManager in a replyList, when one QNetworkReply finished, i
remove it from replyList, when my APP crashed, the replyList has only 50 to 100 QNetworkReplys.