Hello,
I just started using the APR for the File-IO Part of a CGI-Application that
I'm working on.
I'm dealing with a couple of processes performing read/write accesses on
files concurrently, where the reading process locks the file by using
APR_FLOCK_SHARED and the writing process uses APR_FLOCK_EXCLUSIVE.
In my Log-Files I repeatedly spot an error reported by the read-method:
apr_file_read_full returns APR_EOF as status-value.
In the documentation I read the remark that this can happen, but I'm unsure
what could be the true cause and how to deal with this.
<code>
if( ( rv = apr_file_open( &file,
session_file_path,
APR_CREATE |
APR_READ,
APR_OS_DEFAULT, p ) ) )
{
DEBUG_OUT_STR( "Konnte Datei nicht mit Lesezugriff oeffnen",
session_file_path );
DEBUG_OUT_STR( "APR-Error", apr_strerror( rv, error_buf, 1000 ) );
break;
}
if( ( rv = apr_file_lock( file, APR_FLOCK_SHARED ) ) )
{
DEBUG_OUT_STR( "Konnte keinen shared lock auf Datei etablieren",
session_file_path );
DEBUG_OUT_STR( "APR-Error", apr_strerror( rv, error_buf, 1000 ) );
break;
}
if( ( rv = apr_file_info_get( &finfo, APR_FINFO_SIZE, file ) ) )
{
DEBUG_OUT_STR( "Konnte die Dateigroesse nicht ermitteln",
session_file_path );
DEBUG_OUT_STR( "APR-Error", apr_strerror( rv, error_buf, 1000 ) );
break;
}
if( finfo.size )
{
file_size = finfo.size;
self->data = (char*) malloc( ( finfo.size + 1 ) * sizeof( char ) );
if( ( rv =apr_file_read_full( file, self->data, finfo.size,
&file_size
) ) )
{
//This is, where it happens
DEBUG_OUT_STR( "Session-Fehler: Konnte aus Datei nicht lesen:",
session_file_path );
DEBUG_OUT_STR( "APR-Error", apr_strerror( rv, error_buf, 1000 )
);
break;
}
self->data[file_size] = 0;
}
</code>
Is there
i. any mistake in this code-snippet, that could lead to the EOF-Access or
ii. or, if not, a reasonable/unugly strategy to deal with this?
After all, the filesize is determined after establishing the lock, and even
though a problem is reported, the accessed file is not broken at all.
Greets
Sebastian
