Add new argument to info fibres to enable grouping by line/stack

Adds an extra optional, numerical argument to info fibres which lets you specify how many frames "up" to inspect for similarity and group. Check for same-line cases regardless of the value of that numerical argument.

Not passing that optional parameter returns output in the same format as before.

src/libfibre/Poller.cc

@@ -66,12 +66,16 @@ inline void BasePoller::pollLoop(T& This, bool pollerFibre) {
 }
 
 inline int PollerThread::blockingPoll() {
+  int evcnt;
+  for (;;) {
 #if __FreeBSD__
-  int evcnt =  kevent(pollFD, nullptr, 0, events, maxPoll, nullptr); // blocking
+    evcnt =  kevent(pollFD, nullptr, 0, events, maxPoll, nullptr); // blocking
 #else // __linux__ below
-  int evcnt =  epoll_wait(pollFD, events, maxPoll, -1);              // blocking
+    evcnt =  epoll_wait(pollFD, events, maxPoll, -1);              // blocking
 #endif
-  if (evcnt < 0) { GENASSERT1(errno == EINTR, errno); } // gracefully handle EINTR
+    if (evcnt > 0) break;
+    if (evcnt < 0) { GENASSERT1(errno == EINTR, errno); } // gracefully handle EINTR
+  }
   if (paused) pauseSem.P();
   return evcnt;
 }
@@ -116,14 +120,18 @@ void Poller::stop() {
 }
 
 inline int Poller::blockingPoll() {
-  _lfEventEngine->blockPollFD(pollFD);
+  int evcnt;
+  for (;;) {
 #if __FreeBSD__
-  static const timespec ts = Time::zero();
-  int evcnt = kevent(pollFD, nullptr, 0, events, maxPoll, &ts);
+    static const timespec ts = Time::zero();
+    evcnt = kevent(pollFD, nullptr, 0, events, maxPoll, &ts);
 #else // __linux__ below
-  int evcnt =  epoll_wait(pollFD, events, maxPoll, 0);
+    evcnt =  epoll_wait(pollFD, events, maxPoll, 0);
 #endif
-  if (evcnt < 0) { GENASSERT1(errno == EINTR, errno); } // gracefully handle EINTR
+    if (evcnt > 0) break;
+    if (evcnt < 0) { GENASSERT1(errno == EINTR, errno); } // gracefully handle EINTR
+    _lfEventEngine->blockPollFD(pollFD);
+  }
   if (paused) pauseSem.P();
   return evcnt;
 }