Add reusePort argument to ServerSocket.

runtime/bin/socket_linux.cc

Index: runtime/bin/socket_linux.cc
diff --git a/runtime/bin/socket_linux.cc b/runtime/bin/socket_linux.cc
index b9431e17ee64e1f3369f1b2f8523cd2061c8808a..203be0a64ab891b81eab922b39b0b8b4b4e08179 100644
--- a/runtime/bin/socket_linux.cc
+++ b/runtime/bin/socket_linux.cc
@@ -307,11 +307,15 @@ AddressList<InterfaceSocketAddress>* Socket::ListInterfaces(
   return addresses;
 }
 
+#ifndef SO_REUSEPORT
+#define SO_REUSEPORT 15
+#endif  // SO_REUSEPORT
 
 intptr_t ServerSocket::CreateBindListen(RawAddr addr,
                                         intptr_t port,
                                         intptr_t backlog,
-                                        bool v6_only) {
+                                        bool v6_only,
+                                        bool reuse_port) {
   intptr_t fd;
 
   fd = TEMP_FAILURE_RETRY(socket(addr.ss.ss_family, SOCK_STREAM, 0));
@@ -320,6 +324,28 @@ intptr_t ServerSocket::CreateBindListen(RawAddr addr,
   FDUtils::SetCloseOnExec(fd);
 
   int optval = 1;
+
+  if (reuse_port) {
+    if (TEMP_FAILURE_RETRY(setsockopt(fd,
+                                      SOL_SOCKET,
+                                      SO_REUSEPORT,
+                                      &optval,
+                                      sizeof(optval))) != 0) {
+      int e = errno;
+      VOID_TEMP_FAILURE_RETRY(close(fd));
+      errno = e;
+      return -1;
+    }
+  } else {
+    optval = 0;
+    VOID_TEMP_FAILURE_RETRY(setsockopt(fd,
+                                       SOL_SOCKET,
+                                       SO_REUSEPORT,
+                                       &optval,
+                                       sizeof(optval)));
+  }
+
+  optval = 1;
   TEMP_FAILURE_RETRY(
       setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)));