Loader.cpp

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/* Copyright (C) 2009 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

// FIFO queue of load 'functors' with time limit; enables displaying
// load progress without resorting to threads (complicated).

#include "precompiled.h"

#include <deque>
#include <numeric>

#include "lib/timer.h"
#include "CStr.h"
#include "Loader.h"
#include "LoaderThunks.h"


// set by LDR_EndRegistering; may be 0 during development when
// estimated task durations haven't yet been set.
static double total_estimated_duration;

// total time spent loading so far, set by LDR_ProgressiveLoad.
// we need a persistent counter so it can be reset after each load.
// this also accumulates less errors than:
// progress += task_estimated / total_estimated.
static double estimated_duration_tally;

// needed for report of how long each individual task took.
static double task_elapsed_time;

// main purpose is to indicate whether a load is in progress, so that
// LDR_ProgressiveLoad can return 0 iff loading just completed.
// the REGISTERING state allows us to detect 2 simultaneous loads (bogus);
// FIRST_LOAD is used to skip the first timeslice (see LDR_ProgressiveLoad).
static enum
{
    IDLE,
    REGISTERING,
    FIRST_LOAD,
    LOADING
}
state = IDLE;


// holds all state for one load request; stored in queue.
struct LoadRequest
{
    // member documentation is in LDR_Register (avoid duplication).

    LoadFunc func;
    void* param;

    CStrW description;
        // rationale for storing as CStrW here:
        // - needs to be WCS because it's user-visible and will be translated.
        // - don't just store a pointer - the caller's string may be volatile.
        // - the module interface must work in C, so we get/set as wchar_t*.

    int estimated_duration_ms;

    // LDR_Register gets these as parameters; pack everything together.
    LoadRequest(LoadFunc func_, void* param_, const wchar_t* desc_, int ms_)
        : func(func_), param(param_), description(desc_),
          estimated_duration_ms(ms_)
    {
    }
};

typedef std::deque<LoadRequest> LoadRequests;
static LoadRequests load_requests;

// std::accumulate binary op; used by LDR_EndRegistering to sum up all
// estimated durations (for % progress calculation)
struct DurationAdder: public std::binary_function<double, const LoadRequest&, double>
{
    double operator()(double partial_result, const LoadRequest& lr) const
    {
        return partial_result + lr.estimated_duration_ms*1e-3;
    }
};


// call before starting to register load requests.
// this routine is provided so we can prevent 2 simultaneous load operations,
// which is bogus. that can happen by clicking the load button quickly,
// or issuing via console while already loading.
void LDR_BeginRegistering()
{
    ENSURE(state == IDLE);

    state = REGISTERING;
    load_requests.clear();
}


// register a task (later processed in FIFO order).
// <func>: function that will perform the actual work; see LoadFunc.
// <param>: (optional) parameter/persistent state; must be freed by func.
// <description>: user-visible description of the current task, e.g.
//   "Loading Textures".
// <estimated_duration_ms>: used to calculate progress, and when checking
//   whether there is enough of the time budget left to process this task
//   (reduces timeslice overruns, making the main loop more responsive).
void LDR_Register(LoadFunc func, void* param, const wchar_t* description,
    int estimated_duration_ms)
{
    ENSURE(state == REGISTERING);   // must be called between LDR_(Begin|End)Register

    const LoadRequest lr(func, param, description, estimated_duration_ms);
    load_requests.push_back(lr);
}


// call when finished registering tasks; subsequent calls to
// LDR_ProgressiveLoad will then work off the queued entries.
void LDR_EndRegistering()
{
    ENSURE(state == REGISTERING);
    ENSURE(!load_requests.empty());

    state = FIRST_LOAD;
    estimated_duration_tally = 0.0;
    task_elapsed_time = 0.0;
    total_estimated_duration = std::accumulate(load_requests.begin(), load_requests.end(), 0.0, DurationAdder());
}


// immediately cancel this load; no further tasks will be processed.
// used to abort loading upon user request or failure.
// note: no special notification will be returned by LDR_ProgressiveLoad.
void LDR_Cancel()
{
    // the queue doesn't need to be emptied now; that'll happen during the
    // next LDR_StartRegistering. for now, it is sufficient to set the
    // state, so that LDR_ProgressiveLoad is a no-op.
    state = IDLE;
}

// helper routine for LDR_ProgressiveLoad.
// tries to prevent starting a long task when at the end of a timeslice.
static bool HaveTimeForNextTask(double time_left, double time_budget, int estimated_duration_ms)
{
    // have already exceeded our time budget
    if(time_left <= 0.0)
        return false;

    // we haven't started a request yet this timeslice. start it even if
    // it's longer than time_budget to make sure there is progress.
    if(time_left == time_budget)
        return true;

    // check next task length. we want a lengthy task to happen in its own
    // timeslice so that its description is displayed beforehand.
    const double estimated_duration = estimated_duration_ms*1e-3;
    if(time_left+estimated_duration > time_budget*1.20)
        return false;

    return true;
}


// process as many of the queued tasks as possible within <time_budget> [s].
// if a task is lengthy, the budget may be exceeded. call from the main loop.
//
// passes back a description of the next task that will be undertaken
// ("" if finished) and the current progress value.
//
// return semantics:
// - if the final load task just completed, return INFO::ALL_COMPLETE.
// - if loading is in progress but didn't finish, return ERR::TIMED_OUT.
// - if not currently loading (no-op), return 0.
// - any other value indicates a failure; the request has been de-queued.
//
// string interface rationale: for better interoperability, we avoid C++
// std::wstring and PS CStr. since the registered description may not be
// persistent, we can't just store a pointer. returning a pointer to
// our copy of the description doesn't work either, since it's freed when
// the request is de-queued. that leaves writing into caller's buffer.
Status LDR_ProgressiveLoad(double time_budget, wchar_t* description, size_t max_chars, int* progress_percent)
{
    Status ret; // single exit; this is returned
    double progress = 0.0;  // used to set progress_percent
    double time_left = time_budget;

    // don't do any work the first time around so that a graphics update
    // happens before the first (probably lengthy) timeslice.
    if(state == FIRST_LOAD)
    {
        state = LOADING;

        ret = ERR::TIMED_OUT;   // make caller think we did something
        // progress already set to 0.0; that'll be passed back.
        goto done;
    }

    // we're called unconditionally from the main loop, so this isn't
    // an error; there is just nothing to do.
    if(state != LOADING)
        return INFO::OK;

    while(!load_requests.empty())
    {
        // get next task; abort if there's not enough time left for it.
        const LoadRequest& lr = load_requests.front();
        const double estimated_duration = lr.estimated_duration_ms*1e-3;
        if(!HaveTimeForNextTask(time_left, time_budget, lr.estimated_duration_ms))
        {
            ret = ERR::TIMED_OUT;
            goto done;
        }

        // call this task's function and bill elapsed time.
        const double t0 = timer_Time();
        int status = lr.func(lr.param, time_left);
        const bool timed_out = ldr_was_interrupted(status);
        const double elapsed_time = timer_Time() - t0;
        time_left -= elapsed_time;
        task_elapsed_time += elapsed_time;

        // either finished entirely, or failed => remove from queue.
        if(!timed_out)
        {
            debug_printf(L"LOADER| completed %ls in %g ms; estimate was %g ms\n", lr.description.c_str(), task_elapsed_time*1e3, estimated_duration*1e3);
            task_elapsed_time = 0.0;
            estimated_duration_tally += estimated_duration;
            load_requests.pop_front();
        }

        // calculate progress (only possible if estimates have been given)
        if(total_estimated_duration != 0.0)
        {
            double current_estimate = estimated_duration_tally;

            // function interrupted itself; add its estimated progress.
            // note: monotonicity is guaranteed since we never add more than
            //   its estimated_duration_ms.
            if(timed_out)
                current_estimate += estimated_duration * status/100.0;

            progress = current_estimate / total_estimated_duration;
        }

        // do we need to continue?
        // .. function interrupted itself, i.e. timed out; abort.
        if(timed_out)
        {
            ret = ERR::TIMED_OUT;
            goto done;
        }
        // .. failed; abort. loading will continue when we're called in
        //    the next iteration of the main loop.
        //    rationale: bail immediately instead of remembering the first
        //    error that came up so we can report all errors that happen.
        else if(status < 0)
        {
            ret = (Status)status;
            goto done;
        }
        // .. function called LDR_Cancel; abort. return OK since this is an
        //    intentional cancellation, not an error.
        else if(state != LOADING)
        {
            ret = INFO::OK;
            goto done;
        }
        // .. succeeded; continue and process next queued task.
    }

    // queue is empty, we just finished.
    state = IDLE;
    ret = INFO::ALL_COMPLETE;


    // set output params (there are several return points above)
done:
    *progress_percent = (int)(progress * 100.0);
    ENSURE(0 <= *progress_percent && *progress_percent <= 100);

    // we want the next task, instead of what just completed:
    // it will be displayed during the next load phase.
    const wchar_t* new_description = L"";   // assume finished
    if(!load_requests.empty())
        new_description = load_requests.front().description.c_str();
    wcscpy_s(description, max_chars, new_description);

    debug_printf(L"LOADER| returning; desc=%ls progress=%d\n", description, *progress_percent);

    return ret;
}


// immediately process all queued load requests.
// returns 0 on success or a negative error code.
Status LDR_NonprogressiveLoad()
{
    const double time_budget = 100.0;
        // large enough so that individual functions won't time out
        // (that'd waste time).
    wchar_t description[100];
    int progress_percent;

    for(;;)
    {
        Status ret = LDR_ProgressiveLoad(time_budget, description, ARRAY_SIZE(description), &progress_percent);
        switch(ret)
        {
        case INFO::OK:
            debug_warn(L"No load in progress");
            return INFO::OK;
        case INFO::ALL_COMPLETE:
            return INFO::OK;
        case ERR::TIMED_OUT:
            break;          // continue loading
        default:
            WARN_RETURN_STATUS_IF_ERR(ret); // failed; complain
        }
    }
}