MRCommandLoop.h

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#pragma once
#include "exports.h"
#include <queue>
#include <functional>
#include <condition_variable>
#include <mutex>
#include <thread>
 
namespace MR
{
 
// Additional command loop for external app control
class CommandLoop
{
public:
    using CommandFunc = std::function<void()>;
 
    // Specify execution in specific time of application start
    enum class StartPosition
    {
        AfterWindowInit, // executes right after window is initialized
        AfterSplashAppear, // executes after splash appeared
        AfterPluginInit, // executes during splash, after plugins init)
        AfterSplashHide, // executes after splash, to have valid main window context
        AfterWindowAppear // executes after window appeared to have valid opengl context
    };
 
    // This function setups main thread id, it should be called before any command
    MRVIEWER_API static void setMainThreadId( const std::thread::id& id );
    MRVIEWER_API static std::thread::id getMainThreadId();
    // Update state of command loop, only can rise
    MRVIEWER_API static void setState( StartPosition state );
 
    // Adds command to the end of command loop, can be performed from any thread
    // do not block, so be careful with lambda captures
    // note: state - specify execution in specific time of application start
    MRVIEWER_API static void appendCommand( CommandFunc func, StartPosition state = StartPosition::AfterSplashHide );
 
    // If caller thread is main - instantly run command, otherwise add command to the end of loop with
    // StartPosition state = StartPosition::AfterSplash and blocks caller thread until command is done
    MRVIEWER_API static void runCommandFromGUIThread( CommandFunc func );
 
    // Execute all commands from loop
    MRVIEWER_API static void processCommands();
 
    // Return true if loop is empty
    MRVIEWER_API static bool empty();
 
    // Clears the queue without executing the commands
    // if closeLoop is true, does not accept any new commands
    MRVIEWER_API static void removeCommands( bool closeLoop );
 
private:
    CommandLoop() = default;
    ~CommandLoop();
 
    static CommandLoop& instance_();
 
    static void addCommand_( CommandFunc func, bool blockThread, StartPosition state );
 
    struct Command
    {
        CommandFunc func;
        StartPosition state{ StartPosition::AfterSplashHide };
        std::condition_variable callerThreadCV;
        std::thread::id threadId;
    };
 
    StartPosition state_{ StartPosition::AfterWindowInit };
 
    // if set then cannot accept new commands
    bool queueClosed_{ false }; // marked true in `removeCommands`
    std::thread::id mainThreadId_;
    std::queue<std::shared_ptr<Command>> commands_;
    std::mutex mutex_;
};
 
}