How to send a message to all clients connected to TidTcpServer.
lazarus / 38-Networking and Web Programming

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SniperX · 2016-08-04 17:58

I read some post from Remy stating that all the messages to the
connected clients should be sent from within the OnExecute handler
rather than the GUI itself. But then i saw this thread on
stackoverflow http://stackoverflow.com/questions/14173140/tidserver-
about-synchronization-again where a user created a derived class from
TidSeverContext and queued up all the string based messages in it but
what about a scenario where i need to use a combination of more than 2
or more methods from IOHandler class to form a proper message which
could include writing Integer values to socket or TStream or lets say
even a string (just a example).

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Remy Lebeau · 2016-08-10 01:49

Quote from: SniperX on August 04, 2016, 07:58:22 pmI read some post
from Remy stating that all the messages to the connected clients
should be sent from within the OnExecute handler rather than the GUI
itself.

Yes.  That is the safest option.  It prevents 1) deadlocks, 2) failed
clients from causing problems for other clients, and 3) outgoing TCP
messages from overlapping each other on the wire.

Quote from: SniperX on August 04, 2016, 07:58:22 pmBut then i saw this
thread on stackoverflow
http://stackoverflow.com/questions/14173140/tidserver-about-
synchronization-again where a user created a derived class from
TidSeverContext and queued up all the string based messages in it

That is just a convenient way to allow outside threads to add messages
to a client's queue whenever needed, and then that client's OnExecute
event checks the queue for new messages to send to the client.  I have
demonstrated that kind of coding technique with TIdTCPServer many
times.

Quote from: SniperX on August 04, 2016, 07:58:22 pmbut what about a
scenario where i need to use a combination of more than 2 or more
methods from IOHandler class to form a proper message which could
include writing Integer values to socket or TStream or lets say even a
string (just a example).

Once the OnExecute handler detects a queued message is available to be
sent, the code can send the message however it needs to, however many
IOHandler calls it takes.  The point is, by putting all of the writing
logic in OnExecute, outgoing messages are serialized to avoid
overlapping, and the client thread decides when it is safe to send
each message so it does not get interrupted by other things (except
maybe a socket disconnect).  The actual writing logic is up to you,
based on your protocol needs.  Use whatever IOHandler calls you want
per message.  Usually the examples are just strings, but there is
nothing stopping you from sending other kinds of data.