Multithreading problem

From: ArmedCoder (ArmedCoder.1bmjpn_at_mail.codecomments.com)
Date: 08/27/04 

Date: Thu, 26 Aug 2004 19:11:26 -0500

Hi, im just learning about multithreading for a program i am writing
that needs to read from multiple camreas attached to the computer at
the same time.
I know how to create threads and pass around info, and i know a bit
about mutexes but this is not where the problem resides.
Every time the thread goes to open the device at /dev/video* the thread
just stops running as far as i can see.
i put printf's all over the place and it prints right before the open
call on the camera, then the next thread kicks in and does the same
thing.
I know the camreas work cuse when i go back to the non-multithreaded
code, everything works just fine.
Also if i try the open call outside the thread, then pass the camrea
into the thread, they open fine but when the read() call comes, then
the thread dies in the same way.
Does anyone have any ideas whats going on?
Here is the code for the program.

Code:
--------------------
  #include "dispimg.h"
  #include "imggroup.h"
  #include "ifpng.h"
  #include "ifqcam.h"
  #include "error.h"
  #include <stdlib.h>
  #include <stdio.h>
  #include <pthread.h>
  
  #include <sys/ioctl.h>
  #include <sys/mman.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <linux/videodev.h>
  
  #include <X11/Xlib.h>
  #include <X11/Xutil.h>
  #include <X11/Xos.h>
  #include <X11/Xatom.h>
  
  #define SETWIDTH 320
  #define SETHEIGHT 240
  #define SETDEPTH 3
  #define SETFOV 0.1
  #define SETZDIST 50
  #define WINDOWWIDTH 980
  #define WINDOWHEIGHT 480
  #define MAXVIEWS 15
  
  
  // Globals that all files can see
  int imgwidth = SETWIDTH;
  int imgheight = SETHEIGHT;
  int imgdepth = SETDEPTH;
  
  
  extern Display *display;
  extern Window win;
  
  typedef unsigned char * charp;
  
  pthread_mutex_t a_mutex = PTHREAD_MUTEX_INITIALIZER;
  
  
  struct thread_data
  {
  char deviceName[40];
  int device;
  char name[200];
  int maxFrames;
  int xOffset;
  int yOffset;
  char experiment;
  char nopng;
  int cam;
  char isbottom;
  pthread_mutex_t the_mutex;
  };
  
  void * cam_read( void * theInfo )
  {
  int width, height, depth;
  int i, result;
  unsigned char * image;
  struct thread_data *data;
  data = (struct thread_data *)theInfo;
  
  char prefix[200];
  int rc;
  
  fflush(stdout);
  printf( "%s\n", data->deviceName );
  /* rc = pthread_mutex_lock( &a_mutex ); */
  /* if( !rc ) */
  /* { */
  /* printf( "Mutex locked in cam_open\n" ); */
  /* } */
  /* else */
  /* { */
  /* printf( "Cant lock mutex in cam_open\n" ); */
  /* } */
  //data->device = open( data->deviceName, O_RDWR);
  data->device = open_camera( data->deviceName, a_mutex );
  /* if( !rc ) */
  /* { */
  /* printf( "Mutex unlocked in cam_open\n" ); */
  /* } */
  fflush(stdout);
  printf( "%s %d\n", "hi", data->device );
  
  
  for( i = 0; i < data->maxFrames; i++ )
  {
  printf( "%s %i\n", "READ FRAME:", i );
  // read the cam image
  result = qcam_read( data->device, &width, &height, &depth,
                            &image, a_mutex );
  printf( "%d\n", result );
  if( !result )
          {
            printf( "%s %i\n", "BLEAH:", i );
            get_actual_image( image, width, height, depth,
                              data->xOffset, data->yOffset, data->isbottom, 1 );
          }
  
  if( !data->nopng )
          {
            if( !data->experiment )
              {
                sprintf( prefix, "../var/%s_%d/%s_%d %03d.png", data->name, data->cam, data->name, data->cam, i );
              }
            else if ( data->experiment )
              {
                sprintf( prefix, "../var/experiments/image_sequences/%s/%s_%d/%s_%d %03d.png", data->name,
                         data->name, data->cam, data->name,
                         data->cam, i );
              }
            // Ends up looknig like "dirname_cam/frame.png"
            png_write_qcam( prefix, width, height, i, image, data->isbottom );
            //fprintf( stdout, "%s\n", prefix );
          }
  free( image );
  }
  
  close_camera( data->device );
  pthread_exit(0);
  }
  
  
  
  int main (int argc, char ** argv)
  {
  charp image[MAXVIEWS];
  int width[MAXVIEWS], height[MAXVIEWS], depth[MAXVIEWS];
  int xOffSet[MAXVIEWS], yOffSet[MAXVIEWS];
  int error;
  int i, j;
  int gzpx[MAXVIEWS], gzpy[MAXVIEWS], gzpz[MAXVIEWS];
  double pitch[MAXVIEWS], roll[MAXVIEWS], yaw[MAXVIEWS];
  int isbottom[MAXVIEWS];
  int devices[MAXVIEWS]; // Store the camera device(s)
  FILE *stereo; // stereo.dat file pointer
  FILE *directory[MAXVIEWS]; // File pointer for the flatview info in each dir
  int numDirs = 0; // Holds the number of directorys we will be looking at, must be less than MAXVIEWS.
  int maxFrames, currentFrame;
  int viewNum; // Stores the current view being looked at.
  char name[125] = {};// Stores the name of the capture we are working on
  char filename[125];
  FILE *fp;
  char prefix[125];
  
  int nopng = 0; // if 1 no png will be writen.
  int up_down = 0;
  int ud_cam = 0;
  int go = 0;
  int experiment = 0; // if 1 this is capturing an experiment and will create the corect directories accordingly.
  
  pthread_t threads[MAXVIEWS] = {};
  struct thread_data *info[MAXVIEWS] = {};
  
  
  // Get the program flags
  for( i = 0; i < argc; i++ )
  {
  if( !strcmp( argv[i], "-npng" ))
          nopng = 1;
  if( !strcmp( argv[i], "-name" ))
          strcpy( name, argv[++i] );
  if( !strcmp( argv[i], "-exp" ))
          experiment = 1;
  if( !strcmp( argv[i], "-cams" ))
          numDirs = argv[++i];
  if( !strcmp( argv[i], "-u" ))
          up_down = 1;
  if( !strcmp( argv[i], "-go" ))
          go = 1;
  }
  
  if( !go )
  {
  // First get all the info from the user about what we will be caputring
  if( !strcmp( name, "" ) && !nopng)
          {
            fprintf( stdout, "What will this test be called? " );
            fscanf( stdin, "%s", name );
          }
  
  if( numDirs == 0 )
          {
            fprintf( stdout, "How many cameras will we be capturing from? " );
            fscanf( stdin, "%d", &numDirs );
          }
  
  if( up_down )
          {
            fprintf( stdout, "What camera is upside down? " );
            fscanf( stdin, "%d", &ud_cam );
          }
  }
  for( i = 0; i < numDirs; i++ )
  {
  if( !nopng && !go )
          {
            // Get the x, y, z, yaw, pitch, roll for each camera
            fprintf( stdout, "cam %d X pos: ", i+1 );
            fscanf( stdin, "%d", &gzpx[i] );
            fprintf( stdout, "cam %d Y pos: ", i+1 );
            fscanf( stdin, "%d", &gzpy[i] );
            fprintf( stdout, "cam %d Z pos: ", i+1 );
            fscanf( stdin, "%d", &gzpz[i] );
            
            fprintf( stdout, "cam %d Yaw: ", i+1 );
            fscanf( stdin, "%lf", &yaw[i] );
            fprintf( stdout, "cam %d Pitch: ", i+1 );
            fscanf( stdin, "%lf", &pitch[i] );
            fprintf( stdout, "cam %d Roll: ", i+1 );
            fscanf( stdin, "%lf", &roll[i] );
            
            fprintf( stdout, "If the camera is upside down enter 1, otherwise enter 0. " );
            fscanf( stdin, "%d", &isbottom[i] );
            
            // Make the directories that the pics will be stored in
            {
              if( !experiment )
                {
                  sprintf( filename, "mkdir ../var/%s_%d", name, i );
                  //printf( "%s\n", filename );
                }
              else if ( experiment )
                {
                  sprintf( filename, "mkdir ../var/experiments/image_sequences/%s/%s_%d", name, name, i );
                }
              system( filename );
            }
          }
  else
          {
            gzpx[i] = 0;
            gzpy[i] = 0;
            gzpz[i] = 0;
            yaw[i] = 0;
            pitch[i] = 0;
            roll[i] = 0;
            if( up_down == 1 && (ud_cam - 1) == i )
              isbottom[i] = 1;
            else
              isbottom[i] = 0;
          }
  }
  
  if( !nopng )
  {
  fprintf( stdout, "How many frames will we capture? " );
  fscanf( stdin, "%d", &maxFrames );
  }
  else
  {
  maxFrames = 5000;
  }
  
  
  // init the display
  init_display(argv[0],WINDOWWIDTH,WINDOWHEIGHT);
  
  
  // Setup the x and y offset for the images
  for( i = 0; i < numDirs; i++ )
  {
  if( i < 2 )
          {
            xOffSet[i] = ( i % 3 ) * 320;
            yOffSet[i] = ( i / 2 ) * 240;
          }
  if( i >= 2 )
          {
            xOffSet[i] = (( i + 1 ) % 3 ) * 320;
            yOffSet[i] = (( i + 1 ) / 2 ) + 240;
          }
  }
  
  // Write the .dat file for each directory
  if( !nopng )
  {
  for( i = 0; i < numDirs; i++ )
          {
            if( !experiment )
              {
                sprintf( filename, "../var/%s_%d.dat", name, i );
                sprintf( prefix, "%s_%d/%s_%d", name, i, name, i );
              }
            else if ( experiment )
              {
                sprintf( filename, "../var/experiments/image_sequences/%s/%s_%d.dat", name, name, i );
                sprintf( prefix, "experiments/image_sequences/%s/%s_%d/%s_%d", name, name, i, name, i );
              }
            fp = fopen( filename, "w" );
            fprintf( fp, "%s\n%d\n%d\n%d\n%d %d %d\n%lf %lf %lf\n", prefix, 0,
                     currentFrame, 3, gzpx[i], gzpy[i], gzpz[i],
                     yaw[i], pitch[i], roll[i] );
            fclose( fp );
          }
  }
  
  
  // Make all the threads
  for( i = 0; i < numDirs; i++ )
  {
  info[i] = ( struct thread_data* )malloc( sizeof( struct thread_data ));
  sprintf( info[i]->deviceName, "/dev/video%d", i );
  strcpy( info[i]->name, name );
  info[i]->maxFrames = maxFrames;
  info[i]->xOffset = xOffSet[i];
  info[i]->yOffset = yOffSet[i];
  info[i]->nopng = nopng;
  info[i]->experiment = experiment;
  info[i]->cam = i;
  info[i]->isbottom = isbottom[i];
  //info[i]->the_mutex = a_mutex;
  
  pthread_create( &threads[i], 0,
                        cam_read,
                        (void *)info[i]);
  }
  
  /* for( i = 0; i < numDirs; i++ ) */
  /* { */
  /* pthread_join(info[i], 0); */
  /* } */
  
  
  }
-------------------- 

--
ArmedCoder
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