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: ayojs/ayo#82

PR-URL: #20539
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

Author: addaleax

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();
   }