std::Future_error when using std::promise - multithreading

Question

I'm trying to make a video player. I have added a thread to time how long a video should be show on the screen. I'm trying to decode the video and update window in the main thread; the second thread will get the packets, see how long the packet should be displayed, and send the packet to main thread then wait for time to elapse.
For some reason I get this error:
terminate called after throwing an instance of 'std::future_error'
what(): std::future_error: No associated state
What's causing the error?
My Code:
extern "C"{
//FFmpeg libraries
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
//SDL2 libraries
#include <SDL2/SDL.h>
}
// compatibility with newer API
#if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(55,28,1)
#define av_frame_alloc avcodec_alloc_frame
#define av_frame_free avcodec_free_frame
#endif
//C++ libraries
#include <memory>
#include <stdio.h>
#include <iostream>
#include <chrono>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
typedef struct PacketQueue {
AVPacketList *first_pkt, *last_pkt;
} PacketQueue;
std::atomic<bool> quitting;
std::mutex mutex;
std::condition_variable convar;
int packet_queue_put(PacketQueue *q, AVPacket *pkt){
AVPacketList *pkt1;
if(av_dup_packet(pkt) < 0){
return -1;
}
pkt1 = (AVPacketList*) av_malloc(sizeof(AVPacketList));
if(!pkt1){
return -1;
}
pkt1->pkt = *pkt;
pkt1->next = NULL;
std::lock_guard<std::mutex> lock(mutex);
if (!q->last_pkt){
q->first_pkt = pkt1;
}else{
q->last_pkt->next = pkt1;
}
q->last_pkt = pkt1;
convar.notify_all();
return 0;
}
static int packet_queue_get(PacketQueue *q, AVPacket *pkt){
AVPacketList *pkt1;
int ret;
std::unique_lock<std::mutex> lk(mutex);
while(1){
if(quitting){
ret = -1;
break;
}
pkt1 = q->first_pkt;
if(pkt1){
q->first_pkt = pkt1->next;
if(!q->first_pkt){
q->last_pkt = NULL;
}
*pkt = pkt1->pkt;
av_free(pkt1);
ret = 1;
break;
}else {
convar.wait_for(lk, std::chrono::milliseconds(1));
}
}
return ret;
}
void videoTimerFunc(AVRational time_base, PacketQueue* videoq, std::promise<AVPacket> prms){
AVPacket pkt;
int64_t last_pts = 0;
int64_t frameDelay;
AVRational microseconds = {1, 1000000};
while(!quitting){
// Getting packet and check if there are more packets
if(!packet_queue_get(videoq, &pkt)){
// Close programme
quitting = true;
}else {
// Send packet and create timer
frameDelay = av_rescale_q(pkt.dts, time_base, microseconds) - last_pts;
last_pts = av_rescale_q(pkt.dts, time_base, microseconds);
prms.set_value(pkt);
std::this_thread::sleep_for(std::chrono::microseconds(frameDelay));
}
}
}
int main(int argc, char *argv[]){
AVFormatContext* FormatCtx = nullptr;
AVCodecContext* CodecCtxOrig = nullptr;
AVCodecContext* CodecCtx = nullptr;
AVCodec* Codec = nullptr;
int videoStream;
AVFrame* Frame = nullptr;
AVPacket packet;
struct SwsContext* SwsCtx = nullptr;
PacketQueue videoq;
std::promise<AVPacket> pktprms;
std::future<AVPacket> pktftr = pktprms.get_future();
int frameFinished;
int64_t lastPTS;
SDL_Event event;
SDL_Window* screen;
SDL_Renderer* renderer;
SDL_Texture* texture;
std::shared_ptr<Uint8> yPlane, uPlane, vPlane;
int uvPitch;
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
return -1;
}
// Register all formats and codecs
av_register_all();
// Initialise SDL2
if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
fprintf(stderr, "Couldn't initialise SDL - %s\n", SDL_GetError());
return -1;
}
// Setting things up
quitting = false;
memset(&videoq, 0, sizeof(PacketQueue));
// Open video file
if(avformat_open_input(&FormatCtx, argv[1], NULL, NULL) != 0){
fprintf(stderr, "Couldn't open file\n");
return -1; // Couldn't open file
}
// Retrieve stream information
if(avformat_find_stream_info(FormatCtx, NULL) < 0){
fprintf(stderr, "Couldn't find stream information\n");
// Close the video file
avformat_close_input(&FormatCtx);
return -1; // Couldn't find stream information
}
// Find the video stream
videoStream = av_find_best_stream(FormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
if(videoStream < 0){
fprintf(stderr, "Couldn't find video stream\n");
// Close the video file
avformat_close_input(&FormatCtx);
return -1; // Didn't find a video stream
}
// Get a pointer to the codec context for the video stream
CodecCtxOrig = FormatCtx->streams[videoStream]->codec;
// Find the decoder for the video stream
Codec = avcodec_find_decoder(CodecCtxOrig->codec_id);
if(Codec == NULL){
fprintf(stderr, "Unsupported codec\n");
// Close the codec
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1; // Codec not found
}
// Copy context
CodecCtx = avcodec_alloc_context3(Codec);
if(avcodec_copy_context(CodecCtx, CodecCtxOrig) != 0){
fprintf(stderr, "Couldn't copy codec context");
// Close the codec
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1; // Error copying codec context
}
// Open codec
if(avcodec_open2(CodecCtx, Codec, NULL) < 0){
fprintf(stderr, "Couldn't open codec\n");
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1; // Could not open codec
}
// Allocate video frame
Frame = av_frame_alloc();
// Make a screen to put our video
screen = SDL_CreateWindow("Video Player", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, CodecCtx->width, CodecCtx->height, 0);
if(!screen){
fprintf(stderr, "SDL: could not create window - exiting\n");
quitting = true;
// Clean up SDL2
SDL_Quit();
// Free the YUV frame
av_frame_free(&Frame);
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1;
}
renderer = SDL_CreateRenderer(screen, -1, 0);
if(!renderer){
fprintf(stderr, "SDL: could not create renderer - exiting\n");
quitting = true;
// Clean up SDL2
SDL_DestroyWindow(screen);
SDL_Quit();
// Free the YUV frame
av_frame_free(&Frame);
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1;
}
// Allocate a place to put our YUV image on that screen
texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YV12, SDL_TEXTUREACCESS_STREAMING, CodecCtx->width, CodecCtx->height);
if(!texture){
fprintf(stderr, "SDL: could not create texture - exiting\n");
quitting = true;
// Clean up SDL2
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(screen);
SDL_Quit();
// Free the YUV frame
av_frame_free(&Frame);
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1;
}
// Initialise SWS context for software scaling
SwsCtx = sws_getContext(CodecCtx->width, CodecCtx->height, CodecCtx->pix_fmt,
CodecCtx->width, CodecCtx->height, PIX_FMT_YUV420P, SWS_BILINEAR, NULL, NULL, NULL);
if(!SwsCtx){
fprintf(stderr, "Couldn't create sws context\n");
quitting = true;
// Clean up SDL2
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(screen);
SDL_Quit();
// Free the YUV frame
av_frame_free(&Frame);
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1;
}
// set up YV12 pixel array (12 bits per pixel)
yPlane = std::shared_ptr<Uint8>((Uint8 *)::operator new (CodecCtx->width * CodecCtx->height, std::nothrow));
uPlane = std::shared_ptr<Uint8>((Uint8 *)::operator new (CodecCtx->width * CodecCtx->height / 4, std::nothrow));
vPlane = std::shared_ptr<Uint8>((Uint8 *)::operator new (CodecCtx->width * CodecCtx->height / 4, std::nothrow));
uvPitch = CodecCtx->width / 2;
if (!yPlane || !uPlane || !vPlane) {
fprintf(stderr, "Could not allocate pixel buffers - exiting\n");
quitting = true;
// Clean up SDL2
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(screen);
SDL_Quit();
// Free the YUV frame
av_frame_free(&Frame);
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return -1;
}
std::thread videoTimerThread(videoTimerFunc, FormatCtx->streams[videoStream]->time_base, &videoq, std::move(pktprms));
while (!quitting) {
// Check for more packets
if(av_read_frame(FormatCtx, &packet) >= 0){
// Check what stream it belongs to
if (packet.stream_index == videoStream) {
packet_queue_put(&videoq, &packet);
}else{
// Free the packet that was allocated by av_read_frame
av_free_packet(&packet);
}
}
// Check if its time to update
if(pktftr.wait_for(std::chrono::milliseconds(1)) == std::future_status::ready){
// Getting packet
packet = pktftr.get();
// Decode video frame
avcodec_decode_video2(CodecCtx, Frame, &frameFinished, &packet);
// Did we get a video frame?
if (frameFinished) {
AVPicture pict;
pict.data[0] = yPlane.get();
pict.data[1] = uPlane.get();
pict.data[2] = vPlane.get();
pict.linesize[0] = CodecCtx->width;
pict.linesize[1] = uvPitch;
pict.linesize[2] = uvPitch;
// Convert the image into YUV format that SDL uses
sws_scale(SwsCtx, (uint8_t const * const *) Frame->data, Frame->linesize, 0, CodecCtx->height, pict.data, pict.linesize);
SDL_UpdateYUVTexture(texture, NULL, yPlane.get(), CodecCtx->width, uPlane.get(), uvPitch, vPlane.get(), uvPitch);
SDL_RenderClear(renderer);
SDL_RenderCopy(renderer, texture, NULL, NULL);
SDL_RenderPresent(renderer);
}
// Free the packet that was allocated by av_read_frame
av_free_packet(&packet);
}
SDL_PollEvent(&event);
switch (event.type) {
case SDL_QUIT:
quitting = true;
break;
default:
break;
}
}
videoTimerThread.join();
//SDL2 clean up
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(screen);
SDL_Quit();
// Free the YUV frame
av_frame_free(&Frame);
// Free Sws
sws_freeContext(SwsCtx);
// Close the codec
avcodec_close(CodecCtx);
avcodec_close(CodecCtxOrig);
// Close the video file
avformat_close_input(&FormatCtx);
return 0;
}

Answer 1

You can't use std::promise and std::future in a loop. Thanks to Igor Tandetnik, for commenting that.