Dear All,
I need to implement the below mentioned features in my program attached. Any
clue or hint about how to proceed....
Imagining that there are four threads - 2 writers and 2 readers and we have one
shared memory
segment with one block in it.
All threads are contending for the same block of shared memory.
The Writers will write just one message each and the readers will attempt to
read, process and respond.
A typical run would look like this :-
1.Writer 1 & Writer 2 read in a unique buffer from two different files and
store these in malloced blocks of memory.
2. Writer 1 contends for the shared memory segment with the other 3 threads and
if he get it - locks the segment.
3. Writer 1 writes the message to the segment along with a header defining the
length of the buffer
he has written,his thread ID, and a flag showing it is an 'inbound' operation
and then appends the
buffer he has read from file.
He then unlocks the segment. And immediately starts polling to get back a
response.
4. Reader 1 or Reader 2 contend to read from shared memory. Reader 1 wins the
race and locks the block
5. Reader 1 reads in the buffer, parses the header to make sure it is a
'inbound' request,
IF it is a 'inbound' requests he reads in the message as defined by
length field in the header
then xors the buffer or rot13's the buffer and moves to
point 6.
ELSE He unlocks the buffer because it's not an inbound request.
6. Reader 1 then clears that block of shared memory and writes back a header
which has in it
The threadid of the sender, the length of the xor'd or rot13'd buffer and a
flag indicating it is a 'outbound' operation.
He the writes the buffer onto the back of this and unlocks the shared
memory block.
7. Writer 1 is polling for a response. He wins the race with the other 3
threads and locks the block.
He peaks into the shared memory and reads the header.
IF the operation is 'outbound' i.e from a reader thread and the threadid
is his then he moves to point 8.
ELSE he unlocks the blocks because it is not a response for him and or it
is an 'inbound' request from Writer 2.
8. Writer 1 xors or rot13's the response message and then compares it with the
message he sent which he stored in
malloced memory in point 1.
IF it matches he signals success by writing a suitable message to standard
out.
IF it doesn't he writes the block to a error file along with the block he
sent and exits the process witn a suitable error code and
error message to standard error.
When both writer 1 and writer 2 have written their message, got back a response
and check it is correct.
Of course all of this is happening at once. So writer 1 and writer 2 are both
trying to lock the blocks and send 'inbound' messages
and readers 1 and readers 2 are simultaneously trying to lock the same block to
read from it, process the message and respond.
skumar
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