Improve polling for available file descriptors

 - Remove 8MB of memory for each socket created
 - Reduce available file descriptor polling to minimum necessary
   - roughly a 1000 times faster
   - old duration: 34'571'539 ns
   - new duration: 34'464 ns

utilities/xmlrpcpp/src/XmlRpcServer.cpp

@@ -30,26 +30,6 @@ XmlRpcServer::XmlRpcServer()
     _accept_error(false),
     _accept_retry_time_sec(0.0)
 {
-#if !defined(_WINDOWS)
-  struct rlimit limit = { .rlim_cur = 0, .rlim_max = 0 };
-  unsigned int max_files = 1024;
-
-  if(getrlimit(RLIMIT_NOFILE, &limit) == 0) {
-    max_files = limit.rlim_max;
-    if( limit.rlim_max == RLIM_INFINITY ) {
-      max_files = 0;
-    }
-  } else {
-    XmlRpcUtil::error("Could not get open file limit: %s", strerror(errno));
-  }
-  pollfds.resize(max_files);
-  for(unsigned int i=0; i<max_files; i++) {
-    // Set up file descriptor query for all events.
-    pollfds[i].fd = i;
-    pollfds[i].events = POLLIN | POLLPRI | POLLOUT;
-  }
-#endif
-
   // Ask dispatch not to close this socket if it becomes unreadable.
   setKeepOpen(true);
 }
@@ -233,14 +213,33 @@ bool XmlRpcServer::enoughFreeFDs() {
     if( limit.rlim_max == RLIM_INFINITY ) {
       return true;
     }
+  } else {
+    // The man page for getrlimit says that it can fail if the requested
+    // resource is invalid or the second argument is invalid. I'm not sure
+    // either of these can actually fail in this code, but it's better to
+    // check.
+    XmlRpcUtil::error("XmlRpcServer::enoughFreeFDs: Could not get open file "
+                      "limit, getrlimit() failed: %s", strerror(errno));
+    return false;
+  }
 
-    // Poll the available file descriptors.
-    // The POSIX specification guarantees that rlim_cur will always be less or
-    // equal to the process's initial rlim_max, so we don't need an additional
-    // bounds check here.
-    if(poll(&pollfds[0], limit.rlim_cur, 1) >= 0) {
-      for(rlim_t i=0; i<limit.rlim_cur; i++) {
-        if(pollfds[i].revents & POLLNVAL) {
+  // List of all file descriptors, used for counting open files.
+  std::vector<struct pollfd> poll_fds;
+  poll_fds.resize(limit.rlim_cur > FREE_FD_BUFFER ? FREE_FD_BUFFER : limit.rlim_cur);
+
+  // Poll the available file descriptors.
+  // The POSIX specification guarantees that rlim_cur will always be less or
+  // equal to the process's initial rlim_max, so we don't need an additional
+  // bounds check here.
+  for(unsigned long long offset=0; offset<limit.rlim_cur; offset += FREE_FD_BUFFER) {
+    for(unsigned int i=0; i<poll_fds.size(); i++) {
+      // Set up file descriptor query for all events.
+      poll_fds[i].fd = i + offset;
+      poll_fds[i].events = POLLIN | POLLPRI | POLLOUT;
+    }
+    if(poll(&poll_fds[0], poll_fds.size(), 1) >= 0) {
+      for(rlim_t i=0; i<poll_fds.size(); i++) {
+        if(poll_fds[i].revents & POLLNVAL) {
           free_fds++;
         }
         if (free_fds >= FREE_FD_BUFFER) {
@@ -249,18 +248,11 @@ bool XmlRpcServer::enoughFreeFDs() {
         }
       }
     } else {
-      // poll() may fail if interrupted, if the pollfds array is a bad pointer,
+      // poll() may fail if interrupted, if the poll_fds array is a bad pointer,
       // if nfds exceeds RLIMIT_NOFILE, or if the system is out of memory.
       XmlRpcUtil::error("XmlRpcServer::enoughFreeFDs: poll() failed: %s",
                         strerror(errno));
     }
-  } else {
-    // The man page for getrlimit says that it can fail if the requested
-    // resource is invalid or the second argument is invalid. I'm not sure
-    // either of these can actually fail in this code, but it's better to
-    // check.
-    XmlRpcUtil::error("XmlRpcServer::enoughFreeFDs: Could not get open file "
-                      "limit, getrlimit() failed: %s", strerror(errno));
   }
 
   return false;