From 258292366298bbc55e9c3c432efc523dfb394014 Mon Sep 17 00:00:00 2001
From: Richard Schubert <richard.schubert@vay.io>
Date: Tue, 13 Feb 2024 12:25:34 -0600
Subject: [PATCH] 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 | 57 +++++++++++--------------
 1 file changed, 24 insertions(+), 33 deletions(-)

diff --git a/utilities/xmlrpcpp/src/XmlRpcServer.cpp b/utilities/xmlrpcpp/src/XmlRpcServer.cpp
index 99aa24d2f0..28bcf70cd1 100644
--- a/utilities/xmlrpcpp/src/XmlRpcServer.cpp
+++ b/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);
 }
@@ -233,13 +213,31 @@ 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++) {
+  // List of all file descriptors, used for counting open files.
+  pollfds.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<pollfds.size(); i++) {
+      // Set up file descriptor query for all events.
+      pollfds[i].fd = i + offset;
+      pollfds[i].events = POLLIN | POLLPRI | POLLOUT;
+    }
+    if(poll(&pollfds[0], pollfds.size(), 1) >= 0) {
+      for(rlim_t i=0; i<pollfds.size(); i++) {
         if(pollfds[i].revents & POLLNVAL) {
           free_fds++;
         }
@@ -254,13 +252,6 @@ bool XmlRpcServer::enoughFreeFDs() {
       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;