Fixes crashes in unit tests

In the case of multiple dozens of tests running, they will end up
loading and saving the config files dozens of times.
This was causing the configuration system to load in half saved files
that were causing common crashes in the posix unit tests.

Theoretically this could have happened at any time but it looks like
with the posix unit tests added, it is just more likely to happen.

Makes it so loading the configuration file is much more robust and
verbose on failure.
Makes it so saving the config file first saves to a temporary and then
moves in to the correct location. This causes the config saving to be
atomic in a sense so the unit tests won't corrupt other processes of FEX
trying to load the config file.

Source/Common/Config.cpp

@@ -1,9 +1,12 @@
 #include "Common/Config.h"
+#include "LogManager.h"
+
 #include <cassert>
 #include <cstring>
 #include <fstream>
 #include <memory>
 #include <list>
+#include <unistd.h>
 #include <unordered_map>
 #include <vector>
 #include <tiny-json.h>
@@ -28,7 +31,47 @@ namespace FEX::Config {
     return &*alloc->json_objects->emplace(alloc->json_objects->end());
   }
 
+  bool LoadConfigFile(std::vector<char> &Data) {
+    std::fstream ConfigFile;
+    ConfigFile.open("Config.json", std::fstream::in);
+
+    if (!ConfigFile.is_open()) {
+      return false;
+    }
+
+    if (!ConfigFile.seekg(0, std::fstream::end)) {
+      LogMan::Msg::D("Couldn't load configuration file: Seek end");
+      return false;
+    }
+    size_t FileSize = ConfigFile.tellg();
+    if (ConfigFile.fail()) {
+      LogMan::Msg::D("Couldn't load configuration file: tellg");
+      return false;
+    }
+
+    if (!ConfigFile.seekg(0, std::fstream::beg)) {
+      LogMan::Msg::D("Couldn't load configuration file: Seek beginning");
+      return false;
+    }
+
+    if (FileSize > 0) {
+      Data.resize(FileSize);
+      if (ConfigFile.read(&Data.at(0), FileSize)) {
+        LogMan::Msg::D("Couldn't load configuration file: Read");
+        return false;
+      }
+      ConfigFile.close();
+    }
+
+    return true;
+  }
+
   void Init() {
+    std::vector<char> Data;
+    if (!LoadConfigFile(Data)) {
+      return;
+    }
+
     JsonAllocator Pool {
       .PoolObject = {
         .init = PoolInit,
@@ -36,32 +79,36 @@ namespace FEX::Config {
       },
     };
 
-    std::fstream ConfigFile;
-    std::vector<char> Data;
-    ConfigFile.open("Config.json", std::fstream::in);
+    json_t const *json = json_createWithPool(&Data.at(0), &Pool.PoolObject);
+    if (!json) {
+      LogMan::Msg::E("Couldn't create json");
+      return;
+    }
 
-    if (ConfigFile.is_open()) {
-      ConfigFile.seekg(0, std::fstream::end);
-      size_t FileSize = ConfigFile.tellg();
-      ConfigFile.seekg(0, std::fstream::beg);
+    json_t const* ConfigList = json_getProperty(json, "Config");
 
-      if (FileSize > 0) {
-        Data.resize(FileSize);
-        ConfigFile.read(&Data.at(0), FileSize);
-        ConfigFile.close();
+    if (!ConfigList) {
+      LogMan::Msg::E("Couldn't get config list");
+      return;
+    }
 
-        json_t const *json = json_createWithPool(&Data.at(0), &Pool.PoolObject);
-        json_t const* ConfigList = json_getProperty(json, "Config");
+    for (json_t const* ConfigItem = json_getChild(ConfigList);
+      ConfigItem != nullptr;
+      ConfigItem = json_getSibling(ConfigItem)) {
+      const char* ConfigName = json_getName(ConfigItem);
+      const char* ConfigString = json_getValue(ConfigItem);
 
-        for (json_t const* ConfigItem = json_getChild(ConfigList);
-          ConfigItem != nullptr;
-          ConfigItem = json_getSibling(ConfigItem)) {
-          const char* ConfigName = json_getName(ConfigItem);
-          const char* ConfigString = json_getValue(ConfigItem);
-
-          FEX::Config::Add(ConfigName, ConfigString);
-        }
+      if (!ConfigName) {
+        LogMan::Msg::E("Couldn't get config name");
+        return;
       }
+
+      if (!ConfigString) {
+        LogMan::Msg::E("Couldn't get ConfigString for '%s'", ConfigName);
+        return;
+      }
+
+      FEX::Config::Add(ConfigName, ConfigString);
     }
   }
 
@@ -77,13 +124,13 @@ namespace FEX::Config {
     Dest = json_objClose(Dest);
     json_end(Dest);
 
-    std::fstream ConfigFile;
-    ConfigFile.open("Config.json", std::fstream::out);
-
-    if (ConfigFile.is_open()) {
-      ConfigFile.write(Buffer, strlen(Buffer));
-      ConfigFile.close();
-    }
+    // Write the config to a temporary file first then move it to the correct location
+    // This is to solve threading issues when multiple applications are loading and storing the configuration
+    char TmpName[] = "/tmp/ConfigXXXXXXX";
+    int tmp = mkstemp(TmpName);
+    write(tmp, Buffer, strlen(Buffer));
+    close(tmp);
+    rename(TmpName, "Config.json");
 
     ConfigMap.clear();
   }