IXDNSLookup. Uses weak pointer + smart_ptr + shared_from_this instead of static sets + mutex to handle object going away before dns lookup has resolved

ixwebsocket/IXDNSLookup.cpp

@@ -14,27 +14,15 @@ namespace ix
 {
     const int64_t DNSLookup::kDefaultWait = 10; // ms
 
-    std::atomic<uint64_t> DNSLookup::_nextId(0);
-    std::set<uint64_t> DNSLookup::_activeJobs;
-    std::mutex DNSLookup::_activeJobsMutex;
-
     DNSLookup::DNSLookup(const std::string& hostname, int port, int64_t wait) :
         _port(port),
         _wait(wait),
         _res(nullptr),
-        _done(false),
-        _id(_nextId++)
+        _done(false)
     {
         setHostname(hostname);
     }
 
-    DNSLookup::~DNSLookup()
-    {
-        // Remove this job from the active jobs list
-        std::lock_guard<std::mutex> lock(_activeJobsMutex);
-        _activeJobs.erase(_id);
-    }
-
     struct addrinfo* DNSLookup::getAddrInfo(const std::string& hostname,
                                             int port,
                                             std::string& errMsg)
@@ -94,17 +82,14 @@ namespace ix
                             // if you need a second lookup.
         }
 
-        // Record job in the active Job set
-        {
-            std::lock_guard<std::mutex> lock(_activeJobsMutex);
-            _activeJobs.insert(_id);
-        }
-
         //
         // Good resource on thread forced termination
         // https://www.bo-yang.net/2017/11/19/cpp-kill-detached-thread
         //
-        _thread = std::thread(&DNSLookup::run, this, _id, getHostname(), _port);
+        auto ptr = shared_from_this();
+        std::weak_ptr<DNSLookup> self(ptr);
+
+        _thread = std::thread(&DNSLookup::run, this, self, getHostname(), _port);
         _thread.detach();
 
         std::unique_lock<std::mutex> lock(_conditionVariableMutex);
@@ -138,7 +123,7 @@ namespace ix
         return getRes();
     }
 
-    void DNSLookup::run(uint64_t id, const std::string& hostname, int port) // thread runner
+    void DNSLookup::run(std::weak_ptr<DNSLookup> self, const std::string& hostname, int port) // thread runner
     {
         // We don't want to read or write into members variables of an object that could be
         // gone, so we use temporary variables (res) or we pass in by copy everything that
@@ -146,21 +131,15 @@ namespace ix
         std::string errMsg;
         struct addrinfo* res = getAddrInfo(hostname, port, errMsg);
 
-        // if this isn't an active job, and the control thread is gone
-        // there is nothing to do, and we don't want to touch the defunct
-        // object data structure such as _errMsg or _condition
-        std::lock_guard<std::mutex> lock(_activeJobsMutex);
-        if (_activeJobs.count(id) == 0)
+        if (self.lock())
         {
-            return;
+            // Copy result into the member variables
+            setRes(res);
+            setErrMsg(errMsg);
+
+            _condition.notify_one();
+            _done = true;
         }
-
-        // Copy result into the member variables
-        setRes(res);
-        setErrMsg(errMsg);
-
-        _condition.notify_one();
-        _done = true;
     }
 
     void DNSLookup::setHostname(const std::string& hostname)

ixwebsocket/IXDNSLookup.h

@@ -16,16 +16,17 @@
 #include <set>
 #include <string>
 #include <thread>
+#include <memory>
 
 struct addrinfo;
 
 namespace ix
 {
-    class DNSLookup
+    class DNSLookup : public std::enable_shared_from_this<DNSLookup>
     {
     public:
         DNSLookup(const std::string& hostname, int port, int64_t wait = DNSLookup::kDefaultWait);
-        ~DNSLookup();
+        ~DNSLookup() = default;
 
         struct addrinfo* resolve(std::string& errMsg,
                                  const CancellationRequest& isCancellationRequested,
@@ -41,7 +42,7 @@ namespace ix
                                             int port,
                                             std::string& errMsg);
 
-        void run(uint64_t id, const std::string& hostname, int port); // thread runner
+        void run(std::weak_ptr<DNSLookup> self, const std::string& hostname, int port); // thread runner
 
         void setHostname(const std::string& hostname);
         const std::string& getHostname();
@@ -69,11 +70,6 @@ namespace ix
         std::condition_variable _condition;
         std::mutex _conditionVariableMutex;
 
-        uint64_t _id;
-        static std::atomic<uint64_t> _nextId;
-        static std::set<uint64_t> _activeJobs;
-        static std::mutex _activeJobsMutex;
-
         const static int64_t kDefaultWait;
     };
 } // namespace ix

ixwebsocket/IXSocketConnect.cpp

@@ -128,8 +128,8 @@ namespace ix
         //
         // First do DNS resolution
         //
-        DNSLookup dnsLookup(hostname, port);
-        struct addrinfo *res = dnsLookup.resolve(errMsg, isCancellationRequested);
+        auto dnsLookup = std::make_shared<DNSLookup>(hostname, port);
+        struct addrinfo *res = dnsLookup->resolve(errMsg, isCancellationRequested);
         if (res == nullptr)
         {
             return -1;