1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
|
// $Id$
#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(ace, 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);
}
|
