core, frontend: Better progress reporter

A new "quick" decryptor is implemented. This is not really much faster (not slower either) but provides the benefit of being able to report progress on a single file. The frontend is updated accordingly to support this feature.

src/common/thread.h

@@ -0,0 +1,95 @@
+// Copyright 2013 Dolphin Emulator Project / 2014 Citra Emulator Project
+//           2019 threeSD Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <chrono>
+#include <condition_variable>
+#include <cstddef>
+#include <mutex>
+#include <thread>
+
+namespace Common {
+
+class Event {
+public:
+    void Set() {
+        std::lock_guard lk{mutex};
+        if (!is_set) {
+            is_set = true;
+            condvar.notify_one();
+        }
+    }
+
+    void Wait() {
+        std::unique_lock lk{mutex};
+        condvar.wait(lk, [&] { return is_set; });
+        is_set = false;
+    }
+
+    template <class Duration>
+    bool WaitFor(const std::chrono::duration<Duration>& time) {
+        std::unique_lock lk(mutex);
+        if (!condvar.wait_for(lk, time, [this] { return is_set; }))
+            return false;
+        is_set = false;
+        return true;
+    }
+
+    template <class Clock, class Duration>
+    bool WaitUntil(const std::chrono::time_point<Clock, Duration>& time) {
+        std::unique_lock lk{mutex};
+        if (!condvar.wait_until(lk, time, [this] { return is_set; }))
+            return false;
+        is_set = false;
+        return true;
+    }
+
+    void Reset() {
+        std::unique_lock lk{mutex};
+        // no other action required, since wait loops on the predicate and any lingering signal will
+        // get cleared on the first iteration
+        is_set = false;
+    }
+
+private:
+    bool is_set = false;
+    std::condition_variable condvar;
+    std::mutex mutex;
+};
+
+class Barrier {
+public:
+    explicit Barrier(std::size_t count_) : count(count_) {}
+
+    /// Blocks until all "count" threads have called Sync()
+    void Sync() {
+        std::unique_lock lk{mutex};
+        const std::size_t current_generation = generation;
+
+        if (++waiting == count) {
+            generation++;
+            waiting = 0;
+            condvar.notify_all();
+        } else {
+            condvar.wait(lk,
+                         [this, current_generation] { return current_generation != generation; });
+        }
+    }
+
+    std::size_t Generation() const {
+        std::unique_lock lk(mutex);
+        return generation;
+    }
+
+private:
+    std::condition_variable condvar;
+    mutable std::mutex mutex;
+    std::size_t count;
+    std::size_t waiting = 0;
+    std::size_t generation = 0; // Incremented once each time the barrier is used
+};
+
+} // namespace Common