Increase the open file soft limit to the hard limit

On some platforms (macOS), the default soft limit is very low, but the
hard limit is high. So let's just raise it the maximum permitted.

Author: edolstra

src/libmain/shared.cc

@@ -15,6 +15,7 @@
 #include <cstdlib>
 #include <sys/time.h>
 #include <sys/stat.h>
+#include <sys/resource.h>
 #include <unistd.h>
 #include <signal.h>
 #ifdef __linux__
@@ -116,6 +117,26 @@ std::string getArg(const std::string & opt, Strings::iterator & i, const Strings
 static void sigHandler(int signo) {}
 #endif
 
+/**
+ * Increase the open file soft limit to the hard limit. On some
+ * platforms (macOS), the default soft limit is very low, but the hard
+ * limit is high. So let's just raise it the maximum permitted.
+ */
+void bumpFileLimit()
+{
+#ifndef _WIN32
+    struct rlimit limit;
+    if (getrlimit(RLIMIT_NOFILE, &limit) != 0)
+        return;
+
+    if (limit.rlim_cur < limit.rlim_max) {
+        limit.rlim_cur = limit.rlim_max;
+        // Ignore errors, this is best effort.
+        setrlimit(RLIMIT_NOFILE, &limit);
+    }
+#endif
+}
+
 void initNix(bool loadConfig)
 {
     /* Turn on buffering for cerr. */
@@ -183,6 +204,8 @@ void initNix(bool loadConfig)
        now.  In particular, store objects should be readable by
        everybody. */
     umask(0022);
+
+    bumpFileLimit();
 }
 
 LegacyArgs::LegacyArgs(