I am reading the source code of the "File Source" Block and have a question about the source code. In the source code, it firstly opens file by using the d_new_fp variable, then update by using the d_fp variable to replace it. Why not using the d_fp variable to open the file directly instead of replacing d_new_fp with d_fp. It confuses me. I will appreciate it If anyone knows that.
/* -*- c++ -*- */
/*
* Copyright 2012 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio 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 3, or (at your option)
* any later version.
*
* GNU Radio 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 GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <gnuradio/thread/thread.h>
#include "file_source_impl.h"
#include <gnuradio/io_signature.h>
#include <cstdio>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdexcept>
#include <stdio.h>
// win32 (mingw/msvc) specific
#ifdef HAVE_IO_H
#include <io.h>
#endif
#ifdef O_BINARY
#define OUR_O_BINARY O_BINARY
#else
#define OUR_O_BINARY 0
#endif
// should be handled via configure
#ifdef O_LARGEFILE
#define OUR_O_LARGEFILE O_LARGEFILE
#else
#define OUR_O_LARGEFILE 0
#endif
namespace gr {
namespace blocks {
file_source::sptr file_source::make(size_t itemsize, const char *filename, bool repeat)
{
return gnuradio::get_initial_sptr
(new file_source_impl(itemsize, filename, repeat));
}
file_source_impl::file_source_impl(size_t itemsize, const char *filename, bool repeat)
: sync_block("file_source",
io_signature::make(0, 0, 0),
io_signature::make(1, 1, itemsize)),
d_itemsize(itemsize), d_fp(0), d_new_fp(0), d_repeat(repeat),
d_updated(false)
{
open(filename, repeat);
do_update();
}
file_source_impl::~file_source_impl()
{
if(d_fp)
fclose ((FILE*)d_fp);
if(d_new_fp)
fclose ((FILE*)d_new_fp);
}
bool
file_source_impl::seek(long seek_point, int whence)
{
return fseek((FILE*)d_fp, seek_point *d_itemsize, whence) == 0;
}
void
file_source_impl::open(const char *filename, bool repeat)
{
// obtain exclusive access for duration of this function
gr::thread::scoped_lock lock(fp_mutex);
int fd;
// we use "open" to use to the O_LARGEFILE flag
if((fd = ::open(filename, O_RDONLY | OUR_O_LARGEFILE | OUR_O_BINARY)) < 0) {
perror(filename);
throw std::runtime_error("can't open file");
}
if(d_new_fp) {
fclose(d_new_fp);
d_new_fp = 0;
}
if((d_new_fp = fdopen (fd, "rb")) == NULL) {
perror(filename);
::close(fd); // don't leak file descriptor if fdopen fails
throw std::runtime_error("can't open file");
}
//Check to ensure the file will be consumed according to item size
fseek(d_new_fp, 0, SEEK_END);
int file_size = ftell(d_new_fp);
rewind (d_new_fp);
//Warn the user if part of the file will not be consumed.
if(file_size % d_itemsize){
GR_LOG_WARN(d_logger, "WARNING: File will not be fully consumed with the current output type");
}
d_updated = true;
d_repeat = repeat;
}
void
file_source_impl::close()
{
// obtain exclusive access for duration of this function
gr::thread::scoped_lock lock(fp_mutex);
if(d_new_fp != NULL) {
fclose(d_new_fp);
d_new_fp = NULL;
}
d_updated = true;
}
void
file_source_impl::do_update()
{
if(d_updated) {
gr::thread::scoped_lock lock(fp_mutex); // hold while in scope
if(d_fp)
fclose(d_fp);
d_fp = d_new_fp; // install new file pointer
d_new_fp = 0;
d_updated = false;
}
}
int
file_source_impl::work(int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
char *o = (char*)output_items[0];
int i;
int size = noutput_items;
do_update(); // update d_fp is reqd
if(d_fp == NULL)
throw std::runtime_error("work with file not open");
gr::thread::scoped_lock lock(fp_mutex); // hold for the rest of this function
while(size) {
i = fread(o, d_itemsize, size, (FILE*)d_fp);
size -= i;
o += i * d_itemsize;
if(size == 0) // done
break;
if(i > 0) // short read, try again
continue;
// We got a zero from fread. This is either EOF or error. In
// any event, if we're in repeat mode, seek back to the beginning
// of the file and try again, else break
if(!d_repeat)
break;
if(fseek ((FILE *) d_fp, 0, SEEK_SET) == -1) {
fprintf(stderr, "[%s] fseek failed\n", __FILE__);
exit(-1);
}
}
if(size > 0) { // EOF or error
if(size == noutput_items) // we didn't read anything; say we're done
return -1;
return noutput_items - size; // else return partial result
}
return noutput_items;
}
} /* namespace blocks */
} /* namespace gr */
/* -*- c++ -*- */
/*
* Copyright 2012 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio 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 3, or (at your option)
* any later version.
*
* GNU Radio 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 GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef INCLUDED_BLOCKS_FILE_SOURCE_IMPL_H
#define INCLUDED_BLOCKS_FILE_SOURCE_IMPL_H
#include <gnuradio/blocks/file_source.h>
#include <boost/thread/mutex.hpp>
namespace gr {
namespace blocks {
class BLOCKS_API file_source_impl : public file_source
{
private:
size_t d_itemsize;
FILE *d_fp;
FILE *d_new_fp;
bool d_repeat;
bool d_updated;
boost::mutex fp_mutex;
void do_update();
public:
file_source_impl(size_t itemsize, const char *filename, bool repeat);
~file_source_impl();
bool seek(long seek_point, int whence);
void open(const char *filename, bool repeat);
void close();
int work(int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items);
};
} /* namespace blocks */
} /* namespace gr */
#endif /* INCLUDED_BLOCKS_FILE_SOURCE_IMPL_H */