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// $Id$
#include "RMCast_Fragment.h"
#include "ace/Message_Block.h"
#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */
#if !defined (__ACE_INLINE__)
#include "RMCast_Fragment.i"
#endif /* __ACE_INLINE__ */
ACE_RCSID(RMCast, RMCast_Fragment, "$Id$")
ACE_RMCast_Fragment::
ACE_RMCast_Fragment (void)
: ACE_RMCast_Module ()
, max_fragment_size_ (ACE_RMCAST_DEFAULT_FRAGMENT_SIZE)
{
}
ACE_RMCast_Fragment::~ACE_RMCast_Fragment (void)
{
}
int
ACE_RMCast_Fragment::data (ACE_RMCast::Data &received_data)
{
if (this->next () == 0)
return 0;
// The Data object sent downstream
ACE_RMCast::Data data = received_data;
ACE_Message_Block *mb = data.payload;
// @@ We should keep the total size precomputed
data.total_size = ACE_static_cast (ACE_UINT32, mb->total_length ());
// We must leave room for the header
#if defined (ACE_HAS_BROKEN_DGRAM_SENDV)
const int ACE_RMCAST_WRITEV_MAX = ACE_IOV_MAX - 2;
#else
const int ACE_RMCAST_WRITEV_MAX = ACE_IOV_MAX - 1;
#endif /* ACE_HAS_BROKEN_DGRAM_SENDV */
// Assume the header will be included on each fragment, so readuce
// the maximum amount of memory allowed on each fragment....
const size_t fragment_header_size = 1 + 3 * sizeof(ACE_UINT32);
const size_t max_fragment_payload =
this->max_fragment_size_ - fragment_header_size;
// Iterate over all the message blocks in the chain. If there is
// enough data to send an MTU then it is sent immediately.
// The last fragment is sent with whatever data remains.
// A single fragment can expand multiple message blocks, put
// together in an <iovec> array, it is also possible that a single
// message block requires multiple fragments... so the code below is
// as simple as possible, but not any simpler ;-)
// The first piece of each fragment is a header that contains:
// - A sequence number for reassembly, this is unrelated to
// the sequence number for re-transmission.
// NOTE: yes, this increases the bandwidth requires by 4 bytes on
// each message, I don't think this is a big deal.
// - A fragment offset for reassembly.
// - The total size of the message, so the reassembly layer knows
// when a complete message has been received.
// Complete the initialization of the <data> structure
data.fragment_offset = 0;
// The underlying transport layer can only tolerate so many elements
// in a chain, so we must count them and send a fragment if we are
// going over the limit.
ACE_Message_Block blocks[ACE_RMCAST_WRITEV_MAX];
// How many elements of the <blocks> array are in use...
int iovcnt = 0;
// The size of the current message, adding the size of all its
// message blocks.
size_t fragment_size = 0;
for (ACE_Message_Block* b = mb; b != 0; b = b->cont ())
{
ACE_Message_Block *current_block = &blocks[iovcnt];
// Add the block to the vector...
current_block->data_block (b->data_block ()->duplicate ());
current_block->rd_ptr (b->rd_ptr ());
current_block->wr_ptr (b->wr_ptr ());
current_block->cont (0);
// Set the continuation field
if (iovcnt != 0)
blocks[iovcnt-1].cont (current_block);
size_t current_block_length = current_block->length ();
// Recompute the state of the fragment
fragment_size += current_block_length;
iovcnt++;
while (fragment_size >= max_fragment_payload)
{
// We have filled a fragment. It is possible that we need
// to split the last message block in multiple fragments,
// thus the loop above...
// First adjust the last message block to exactly fit in the
// fragment:
size_t last_sent_mb_len =
max_fragment_payload - (fragment_size - current_block_length);
// Send only enough data of the last message block to fill
// the fragment...
current_block->wr_ptr (current_block->rd_ptr ()
+ last_sent_mb_len);
data.payload = blocks;
if (this->next ()->data (data) == -1)
return -1;
// adjust the offset
data.fragment_offset += ACE_static_cast (ACE_UINT32,
max_fragment_payload);
// Now compute how much data is left in the last message
// block, to check if we should continue sending it...
current_block_length -= last_sent_mb_len;
if (current_block_length == 0)
{
// No more data from this message block, just continue
// the outer loop...
iovcnt = 0;
fragment_size = 0;
blocks[0].cont (0);
break; // while
}
// There is some data left, we try to send it in a single
// fragment, if it is still too big the beginning of this
// loop will adjust things.
// We must put the data in the right place in the array..
char *rd_ptr = current_block->rd_ptr () + last_sent_mb_len;
char *wr_ptr = rd_ptr + current_block_length;
blocks[0].data_block (current_block->replace_data_block (0));
// And determine what segment of the data will be sent..
blocks[0].rd_ptr (rd_ptr);
blocks[0].wr_ptr (wr_ptr);
blocks[0].cont (0);
// Adjust the state of the fragment
fragment_size = current_block_length;
iovcnt = 1;
// Notice that if <fragment_size> is too big the start of
// this loop will continue the fragmentation.
}
// It is also possible to fill up the iovec array before the
// fragment is completed, in this case we must send whatever we
// have:
if (iovcnt == ACE_RMCAST_WRITEV_MAX)
{
if (this->next ()->data (data) == -1)
return -1;
iovcnt = 0;
fragment_size = 0;
blocks[0].cont (0);
}
}
if (iovcnt == 0)
return 0;
return this->next ()->data (data);
}
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