s_async.h

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/*
Minetest
Copyright (C) 2013 sapier, <sapier AT gmx DOT net>
 
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.
 
You should have received a copy of the GNU Lesser General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
 
#pragma once
 
#include <vector>
#include <deque>
#include <unordered_set>
#include <memory>
 
#include <lua.h>
#include "threading/semaphore.h"
#include "threading/thread.h"
#include "common/c_packer.h"
#include "cpp_api/s_base.h"
#include "cpp_api/s_security.h"
 
// Forward declarations
class AsyncEngine;
 
 
// Declarations
 
// Data required to queue a job
struct LuaJobInfo
{
    LuaJobInfo() = default;
 
    // Function to be called in async environment (from string.dump)
    std::string function;
    // Parameter to be passed to function (serialized)
    std::string params;
    // Alternative parameters
    std::unique_ptr<PackedValue> params_ext;
    // Result of function call (serialized)
    std::string result;
    // Alternative result
    std::unique_ptr<PackedValue> result_ext;
    // Name of the mod who invoked this call
    std::string mod_origin;
    // JobID used to identify a job and match it to callback
    u32 id;
};
 
// Asynchronous working environment
class AsyncWorkerThread : public Thread,
    virtual public ScriptApiBase, public ScriptApiSecurity {
    friend class AsyncEngine;
public:
    virtual ~AsyncWorkerThread();
 
    void *run();
 
protected:
    AsyncWorkerThread(AsyncEngine* jobDispatcher, const std::string &name);
 
private:
    AsyncEngine *jobDispatcher = nullptr;
    bool isErrored = false;
};
 
// Asynchornous thread and job management
class AsyncEngine {
    friend class AsyncWorkerThread;
    typedef void (*StateInitializer)(lua_State *L, int top);
public:
    AsyncEngine() = default;
    AsyncEngine(Server *server) : server(server) {};
    ~AsyncEngine();
 
    void registerStateInitializer(StateInitializer func);
 
    void initialize(unsigned int numEngines);
 
    u32 queueAsyncJob(std::string &&func, std::string &&params,
            const std::string &mod_origin = "");
 
    u32 queueAsyncJob(std::string &&func, PackedValue *params,
            const std::string &mod_origin = "");
 
    void step(lua_State *L);
 
protected:
    bool getJob(LuaJobInfo *job);
 
    void putJobResult(LuaJobInfo &&result);
 
    void addWorkerThread();
 
    void stepJobResults(lua_State *L);
 
    void stepAutoscale();
 
    bool prepareEnvironment(lua_State* L, int top);
 
private:
    // Variable locking the engine against further modification
    bool initDone = false;
 
    // Maximum number of worker threads for automatic scaling
    // 0 if disabled
    unsigned int autoscaleMaxWorkers = 0;
    u64 autoscaleTimer = 0;
    std::unordered_set<u32> autoscaleSeenJobs;
 
    // Only set for the server async environment (duh)
    Server *server = nullptr;
 
    // Internal store for registred state initializers
    std::vector<StateInitializer> stateInitializers;
 
    // Internal counter to create job IDs
    u32 jobIdCounter = 0;
 
    // Mutex to protect job queue
    std::mutex jobQueueMutex;
    // Job queue
    std::deque<LuaJobInfo> jobQueue;
 
    // Mutex to protect result queue
    std::mutex resultQueueMutex;
    // Result queue
    std::deque<LuaJobInfo> resultQueue;
 
    // List of current worker threads
    std::vector<AsyncWorkerThread*> workerThreads;
 
    // Counter semaphore for job dispatching
    Semaphore jobQueueCounter;
};