Only initialize libcurl once.

include/instance.hpp

@@ -26,6 +26,9 @@ namespace mastodonpp
 
 using std::string;
 
+//! Internal use only.
+extern bool curl_initialized;
+
 /*!
  *  @brief  Holds the access data of and the connection to an instance.
  *
@@ -39,6 +42,11 @@ public:
     /*!
      *  @brief  Construct a new Instance object.
      *
+     *  The first construction of an Instance object will call
+     *  `curl_global_init`, which is not thread-safe. For more information
+     *  consult [curl_global_init(3)]
+     *  (https://curl.haxx.se/libcurl/c/curl_global_init.html).
+     *
      *  @param  instance     The hostname of the instance.
      *  @param  access_token Your access token.
      *

src/instance.cpp

@@ -24,16 +24,29 @@ namespace mastodonpp
 
 using std::move;
 
+bool curl_initialized{false};
+
 Instance::Instance(string instance, string access_token)
     : _instance{move(instance)}
     , _access_token{move(access_token)}
-    , _connection{curl_easy_init()}
 {
+    if (!curl_initialized)
+    {
+        curl_global_init(CURL_GLOBAL_DEFAULT);
+        curl_initialized = true;
+    }
+    _connection = curl_easy_init();
     setup_curl();
 }
 Instance::~Instance()
 {
     curl_easy_cleanup(_connection);
+
+    if (curl_initialized)
+    {
+        curl_global_cleanup();
+        curl_initialized = false;
+    }
 }
 
 int Instance::writer(char *data, size_t size, size_t nmemb, string *writerData)