1 files changed, 98 insertions, 0 deletions
diff --git a/src/lib/thread/numcpus.c b/src/lib/thread/numcpus.c
new file mode 100644
index 0000000000..b293d965d2
--- /dev/null
+++ b/src/lib/thread/numcpus.c
@@ -0,0 +1,98 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file numcpus.c
+ * \brief Compute the number of CPUs configured on this system.
+ **/
+
+#include "orconfig.h"
+#include "lib/thread/numcpus.h"
+#include "lib/log/log.h"
+#include "lib/log/util_bug.h"
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+#include <stdlib.h>
+
+/** Implementation logic for compute_num_cpus(). */
+static int
+compute_num_cpus_impl(void)
+{
+#ifdef _WIN32
+  SYSTEM_INFO info;
+  memset(&info, 0, sizeof(info));
+  GetSystemInfo(&info);
+  if (info.dwNumberOfProcessors >= 1 && info.dwNumberOfProcessors < INT_MAX)
+    return (int)info.dwNumberOfProcessors;
+  else
+    return -1;
+#elif defined(HAVE_SYSCONF)
+#ifdef _SC_NPROCESSORS_CONF
+  long cpus_conf = sysconf(_SC_NPROCESSORS_CONF);
+#else
+  long cpus_conf = -1;
+#endif
+#ifdef _SC_NPROCESSORS_ONLN
+  long cpus_onln = sysconf(_SC_NPROCESSORS_ONLN);
+#else
+  long cpus_onln = -1;
+#endif
+  long cpus = -1;
+
+  if (cpus_conf > 0 && cpus_onln < 0) {
+    cpus = cpus_conf;
+  } else if (cpus_onln > 0 && cpus_conf < 0) {
+    cpus = cpus_onln;
+  } else if (cpus_onln > 0 && cpus_conf > 0) {
+    if (cpus_onln < cpus_conf) {
+      log_notice(LD_GENERAL, "I think we have %ld CPUS, but only %ld of them "
+                 "are available. Telling Tor to only use %ld. You can over"
+                 "ride this with the NumCPUs option",
+                 cpus_conf, cpus_onln, cpus_onln);
+    }
+    cpus = cpus_onln;
+  }
+
+  if (cpus >= 1 && cpus < INT_MAX)
+    return (int)cpus;
+  else
+    return -1;
+#else
+  return -1;
+#endif /* defined(_WIN32) || ... */
+}
+
+#define MAX_DETECTABLE_CPUS 16
+
+/** Return how many CPUs we are running with.  We assume that nobody is
+ * using hot-swappable CPUs, so we don't recompute this after the first
+ * time.  Return -1 if we don't know how to tell the number of CPUs on this
+ * system.
+ */
+int
+compute_num_cpus(void)
+{
+  static int num_cpus = -2;
+  if (num_cpus == -2) {
+    num_cpus = compute_num_cpus_impl();
+    tor_assert(num_cpus != -2);
+    if (num_cpus > MAX_DETECTABLE_CPUS) {
+      /* LCOV_EXCL_START */
+      log_notice(LD_GENERAL, "Wow!  I detected that you have %d CPUs. I "
+                 "will not autodetect any more than %d, though.  If you "
+                 "want to configure more, set NumCPUs in your torrc",
+                 num_cpus, MAX_DETECTABLE_CPUS);
+      num_cpus = MAX_DETECTABLE_CPUS;
+      /* LCOV_EXCL_STOP */
+    }
+  }
+  return num_cpus;
+}