<p><b>@mmd-osm</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/openstreetmap/osm2pgsql/pull/960#discussion_r334763876">db-copy.cpp</a>:</p>
<pre style='color:#555'>> @@ -28,9 +28,18 @@ db_copy_thread_t::~db_copy_thread_t() { finish(); }
 void db_copy_thread_t::add_buffer(std::unique_ptr<db_cmd_t> &&buffer)
 {
     assert(m_worker.joinable()); // thread must not have been finished
-    std::unique_lock<std::mutex> lock(m_queue_mutex);
-    m_worker_queue.push_back(std::move(buffer));
-    m_queue_cond.notify_one();
+
+    for (;;) {
+        std::unique_lock<std::mutex> lock(m_queue_mutex);
+        if (m_worker_queue.size() >= db_cmd_copy_t::Max_buffers) {
+            m_queue_full_cond.wait(lock);
</pre>
<p>just checked how this is done in <em>c++ concurrency in action</em>. They use a lambda function for the condition variable wait method: <a href="https://github.com/anthonywilliams/ccia_code_samples/blob/master/listings/listing_4.1.cpp#L47">https://github.com/anthonywilliams/ccia_code_samples/blob/master/listings/listing_4.1.cpp#L47</a> (code example is not about a bounded queue, it's just to show how they use condition variables throughout chapter 4).</p>

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