fix: prevent EDEADLK self-join in ~CurlHttpOperation on async-thread destruction

lib/http/HttpClient_Curl.cpp

@@ -84,7 +84,13 @@ namespace MAT_NS_BEGIN {
         auto curlOperation = std::make_shared<CurlHttpOperation>(curlRequest->m_method, curlRequest->m_url, callback, requestHeaders, curlRequest->m_body, false, HTTP_CONN_TIMEOUT, m_sslVerify, sslCaInfo);
         curlRequest->SetOperation(curlOperation);
 
-        // The lifetime of curlOperation is guarnteed by the call to result.wait() in the d'tor.  
+        // The lifetime of curlOperation across the async Send is guaranteed by
+        // ~CurlHttpOperation. After this function returns, the only remaining
+        // shared_ptr is the one held by the owning CurlHttpRequest. When that
+        // request is destroyed from another thread, the destructor waits for the
+        // async result; if the callback below leads to the request being
+        // destroyed on the async thread itself (OnHttpResponse ->
+        // EventsUploadContext::clear()), the destructor defers the join instead.
         curlOperation->SendAsync([this, callback, requestId](CurlHttpOperation& operation) {
             this->EraseRequest(requestId);
 

lib/http/HttpClient_Curl.hpp

@@ -22,6 +22,8 @@
 #include <numeric>
 #include <future>
 #include <atomic>
+#include <thread>
+#include <new>
 
 #include <poll.h>
 #include <curl/curl.h>
@@ -173,11 +175,58 @@ class CurlHttpOperation {
      */
     virtual ~CurlHttpOperation()
     {
-        // Given the request has not been aborted we should wait for completion here
-        // This guarantees the lifetime of this request.
+        // libstdc++'s std::future<>::~future implicitly joins the async thread
+        // during destruction. If this destructor runs ON that same async thread
+        // (the async callback led to the owning CurlHttpRequest being destroyed
+        // on that thread, e.g. OnHttpResponse -> EventsUploadContext::clear()),
+        // that join is a self-join and throws std::system_error("Resource
+        // deadlock avoided"); since it originates in this noexcept destructor it
+        // aborts the process.
+        //
+        // Distinguish the two cases by the thread id published when the async
+        // task started:
+        //   * self-join   -> Send() has returned (we are running inside its
+        //                    callback), but the async task itself has not yet
+        //                    returned (this destructor is executing inside it),
+        //                    so defer the future's join to a detached helper
+        //                    thread rather than joining on this (the async)
+        //                    thread; the helper's join completes once the task
+        //                    returns after this destructor unwinds.
+        //   * cross-thread -> the async Send() may still be running, so wait()
+        //                    to keep the curl handle, response buffer and the
+        //                    by-reference request body alive until it finishes.
         if (result.valid())
         {
-            result.wait();
+            if (m_asyncThreadIdSet.load(std::memory_order_acquire) &&
+                std::this_thread::get_id() == m_asyncThreadId)
+            {
+                // Heap-allocate first so a rare std::thread spawn failure leaks
+                // the already-finished future rather than joining it on this
+                // async thread (EDEADLK) or letting std::system_error escape
+                // this noexcept destructor.
+                std::future<long>* pending = new (std::nothrow) std::future<long>(std::move(result));
+                if (pending == nullptr)
+                {
+                    // Out of memory: `result` is still valid and would self-join
+                    // (EDEADLK) when destroyed on this async thread at the end of
+                    // the destructor, and there is no allocation-free way to move
+                    // it off-thread. Abort as a last resort rather than fall
+                    // through to a guaranteed EDEADLK abort.
+                    std::abort();
+                }
+                try
+                {
+                    std::thread([pending]() { delete pending; }).detach();
+                }
+                catch (...)
+                {
+                    // Thread exhaustion: intentionally leak *pending.
+                }
+            }
+            else
+            {
+                result.wait();
+            }
         }
         DispatchEvent(OnDestroy);
         res = CURLE_OK;
@@ -318,7 +367,13 @@ class CurlHttpOperation {
     }
 
     std::future<long> & SendAsync(std::function<void(CurlHttpOperation &)> callback = nullptr) {
+        // Reset the publication flag before launching so self-join detection
+        // stays correct even if this operation were ever reused (today each
+        // CurlHttpOperation is single-use: one SendAsync call per request).
+        m_asyncThreadIdSet.store(false, std::memory_order_release);
         result = std::async(std::launch::async, [this, callback] {
+            m_asyncThreadId = std::this_thread::get_id();
+            m_asyncThreadIdSet.store(true, std::memory_order_release);
             long result = Send();
             if (callback!=nullptr)
                 callback(*this);
@@ -437,6 +492,15 @@ class CurlHttpOperation {
 
     CURL *curl;                     // Local curl instance
     CURLcode res = CURLE_OK;        // Curl result OR HTTP status code if successful
+
+    // Id of the thread running the async Send() task, published via the
+    // atomic<bool> flag below (release/acquire). ~CurlHttpOperation uses these
+    // to detect a self-join (destruction from within the async callback) and
+    // avoid the EDEADLK that joining the future would raise. A plain thread::id
+    // plus an atomic<bool> flag is used instead of std::atomic<std::thread::id>,
+    // which is not guaranteed to be supported across standard libraries.
+    std::thread::id m_asyncThreadId{};
+    std::atomic<bool> m_asyncThreadIdSet{ false };
 
     IHttpResponseCallback* m_callback = nullptr;