From 90a2a545e2d96a92618a6a0dd8a94cc1cf4440a9 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Mon, 4 Sep 2017 22:31:20 +0200
Subject: [PATCH] src: use lock for c-ares library init/cleanup

This helps embedders wishing to use Node.js in a multi-threaded fashion
and helps pave the way for thread-based worker support.

Thanks to Stephen Belanger for reviewing this commit in its original PR.

Refs: https://github.com/ayojs/ayo/pull/82
---
 src/cares_wrap.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/cares_wrap.cc b/src/cares_wrap.cc
index 4df47d75d43ba8..4208c02d4fe445 100644
--- a/src/cares_wrap.cc
+++ b/src/cares_wrap.cc
@@ -70,6 +70,8 @@ using v8::Value;
 
 namespace {
 
+Mutex ares_library_mutex;
+
 inline uint16_t cares_get_16bit(const unsigned char* p) {
   return static_cast<uint32_t>(p[0] << 8U) | (static_cast<uint32_t>(p[1]));
 }
@@ -470,6 +472,7 @@ void ChannelWrap::Setup() {
 
   int r;
   if (!library_inited_) {
+    Mutex::ScopedLock lock(ares_library_mutex);
     // Multiple calls to ares_library_init() increase a reference counter,
     // so this is a no-op except for the first call to it.
     r = ares_library_init(ARES_LIB_INIT_ALL);
@@ -483,6 +486,7 @@ void ChannelWrap::Setup() {
                         ARES_OPT_FLAGS | ARES_OPT_SOCK_STATE_CB);
 
   if (r != ARES_SUCCESS) {
+    Mutex::ScopedLock lock(ares_library_mutex);
     ares_library_cleanup();
     return env()->ThrowError(ToErrorCodeString(r));
   }
@@ -500,6 +504,7 @@ void ChannelWrap::Setup() {
 
 ChannelWrap::~ChannelWrap() {
   if (library_inited_) {
+    Mutex::ScopedLock lock(ares_library_mutex);
     // This decreases the reference counter increased by ares_library_init().
     ares_library_cleanup();
   }