Probleme world generation with thread - c++

Question

I'm trying to create a world generation system.
I have a world class that contain a map of terrain that can be increased during the program.
When I do it in the main thread it work fine but their is little freeze when he calculate the vertex and everything, so I tried to use Thread.
So to generate a terrain I do that :
std::thread newThread(&World::addTerrain, this, xIndex, zIndex, 64, 64);
newThread.detach();
(The addTerrain method)
void World::addTerrain(int x, int z, size_t len, size_t col) {
//allTerrain_[x].emplace(std::make_pair(z, Terrain(x*size_, z*size_, size_ / 2.0f, len, col, &shader_, &heightGenerator_)));
allTerrain_[x].emplace(std::make_pair(z, Terrain(x*size_, z*size_, size_/2.0f, len, col, &shader_, &waterShader_, &heightGenerator_)));
}
but when I do this, the new terrain is added to the map, but he look empty (nothing is drawn).
I'm not sure I'm using the right approach, so if you can help me it will be great !

Answer 1

Try this:
Add a mutex to World (terrain_mutex_)
Use a std::lock_guard<std::mutex> when reading from/writing to allTerrain_. Your painting code needs to use this mutex too.
In addTerrain:
void World::addTerrain(int x, int z, size_t len, size_t col) {
{ // lock while copying the terrain
std::lock_guard<std::mutex> guard(terrain_mutex_);
auto terrain_copy = allTerrain_;
}
// add more terrain to the copy
terrain_copy[x].emplace(z, Terrain(x*size_, z*size_, size_/2.0f, len, col,
&shader_, &waterShader_, &heightGenerator_));
{ // lock when swapping in the copy
std::lock_guard<std::mutex> guard(terrain_mutex_);
std::swap(terrain_copy, allTerrain_);
}
}