[Libevent-users] Different behavior of my code

[Bernd Schoeller <bernd.schoeller@xxxxxxxxx>]

Dear List,

I am currently taking my first steps in experimenting with libevent. To 
do that, I have written the small example below that should copy a file. 
I am currently trying to restrict myself to the core functions, and I 
know that the buffer handling is too primitive.

I am trying the code on 3 different platforms:

a) On OpenBSD 4.9, the code seems to work and the file is copied. I am 
not sure what version OpenBSD is using and what they changed.

b) On MacOS Lion, using libevent 2.0.10, the program copies the file, 
but seems to never receive the 0 bytes EOF read, thus blocking after the 
last write. Output ends with:

...
read callback
Read: 6, 2 - 81953
write callback
Written: 7, 4 - 81953 (81953) of 81953
Sub read.

c) On Linux (Ubuntu LTS), using libevent 1.4.13, the read operation is 
never triggered and the main loop exits immediately. The output printed is:

Starting.
Opened read file handle 6.
Opened write file handle 7.
Exited with 1

With these 3 different behaviors, I am pretty sure that I have not 
understood some fundamental detail of libevent. I do not think the 
different versions are to blame, and it should be possible to create 
some code that runs on all versions, as I am using very basic functions 
that seem to be the same in all versions.

Thanks for your help,
Bernd


---> c_libevent_test.c <---

#include <event.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

#define READ_FILE_NAME "in.dat"
#define WRITE_FILE_NAME "out.dat"

#define BUFFER_SIZE 100000

struct event fd_read;
struct event fd_write;

int buffer[BUFFER_SIZE];
int full;
int written;

void onRead(int fd, short mode, void* data)
{
  printf("read callback\n");
  full = read(fd, buffer, BUFFER_SIZE);
  printf("Read: %d, %d - %d\n", fd, mode, full);
  if (full > 0) {
    written = 0;
    event_add(&fd_write, NULL);
  }
}

void onWrite(int fd, short mode, void *data)
{
  printf("write callback\n");
  int wr = write(fd, buffer+written, full-written);
  written += wr;
  printf("Written: %d, %d - %d (%d) of %d\n", fd, mode,
         wr, written, full);
  if (wr >= full) {
    written = 0;
    full = 0;
    printf("Sub read.\n");
    event_add(&fd_read, NULL);
  } else {
    event_add(&fd_write, NULL);
  }
}

int main(int argc, char** argv)
{
  full = 0;

  event_init();

  printf("Starting.\n");

  int fd;
  fd = open(READ_FILE_NAME, O_RDONLY);
  printf("Opened read file handle %d.\n", fd);
  event_set(&fd_read, fd, EV_READ, onRead, 0);

  fd = open(WRITE_FILE_NAME, O_WRONLY | O_CREAT, 0600);
  printf("Opened write file handle %d.\n", fd);
  event_set(&fd_write, fd, EV_WRITE, onWrite, 0);

  event_add(&fd_read, NULL);
  printf("Exited with %d\n", event_dispatch());
  return 0;
}

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