That's because only a few system calls can be safely called inside signals. Only calls that are re-entrant or not interruptible by signals can be called safely.
This can happen if XML documents are parsed infrequently, or if the number of threads within your application varies widely (Xerces-C++ parsers are not re-entrant).
如果不经常解析 XML 文档，或者应用程序中的线程数量变化很大（Xerces-C++ 解析器不支持再次进入），就会出现这种情况。
3
Concurrency in the java.util.concurrent collection is enabled via re-entrant read-write locks and is now supported natively inside Terracotta 2.4.