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Satoshi Client Operation: Initialization and Thread Startup
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Note that the client uses a fixed number of threads that are created on
startup. All of the reading and writing on active network sockets are
handled by one thread.

The main() entry point to the program is in init.cpp. Do not go looking in
main.cpp for main() - you will not find it.

The first thing main() does is call AppInit, which calls AppInit2 which
performs a bunch of initialization busy work mostly related to how the
application handles errors. At some point AppInit2 calls ParseParameters,
and then some argument handling code processes some basic arguments.

Now it checks to see if an existing GUI window is already present and if so,
brings it to the foreground.

Next it creates a lock file in the bitcoin directory and if bitcoin is already
running, displays a message and exits.

Next it attemps to listen on the bitcoin port, and if the port is already in
user or other error, displays a message and exits.

Next it loads IP addresses from a database, then it loads the block index, and
then it loads the wallet.

Next it gets the top block number from the wallet, or zero if -rescan is used.
Then It scans the block chain from the block number above.

Side Note:
    Note that printf has been redefined in util.h. So printf is really
    OutputDebugStringF which directs to a file if appropriate (see util.h
    and util.cpp). Also "loop" is defined in util.h as for (  ; ;  ).

Then it does a bit more initialization and parameter processing and then it
finally opens the GUI main window.

Next it creates two threads:

    1. StartNode()
    2. And if acting as server: ThreadRPCServer()
This is the only place where these threads are created.

StartNode() is in net.cpp and ThreadRPCServer() is in rpc.cpp.

Last, if not compiled for the GUI it sleeps for 5 seonds in an infinite loop.



-- Thread StartNode() in net.cpp --

StartNode is sort of a master networking thread.

First it creates a CNode for the localhost 127.0.0.1 internal addresss to
handle communication.

Next, it gets the local IP address. On windows, its a lookup using the
local host name. On Linux, it is the first IP address it finds on an
interface that is up and is not the loopback interface.

Next it creates a thread (ThreadGetMyExternalIP) to confirm the local IP
address using 3rd party verification. If using a proxy, it does not
bother, because it will not take incoming connections.

Next, if Universal Plug and Play is used, then a thread (ThreadMapPort)
to deal with port mapping is created.

Next it creates a thread (ThreadIRCSeed) to exchange IP addresses.

Next it creates a thread (ThreadSocketHandler) to "Send and receive from
sockets, accept connections".

Next it creates a thread (ThreadOpenConnections) to initiate outbound
connections.

Next it creates a thread (ThreadMessageHandler) to process messages.

Finally, if you have specified so, it will start a bitcoin mining thread.



-- Thread IRCSeed in net.cpp --

Connects to 92.243.23.21 port 6667, JOINs the channel, and then
reads lines one at a time looking for other users.


-- Thread ThreadSocketHandler in net.cpp --

Goes into an endless loop servicing sockets that need servicing.
Handles disconnected nodes.
Prepares "select" descriptor list and then calls select, waiting for
I/O on all the relevant sockets with a 50ms timeout.
Process new incoming connection on listening socket. Create a CNode for them.
Handle receiving and sending.
Set sockets that have not done anything to disconnected state.


-- Thread ThreadOpenConnecions in net.cpp --

Figures out nodes from parameters, seeds, irc, etc, and then goes into a
loop, connecting to each one by one.


-- Thread ThreadMessageHandler in net.cpp

This thread goes through all the nodes and calls ProcessMessages(pnode) in
main.cpp which looks for valid messages on the node receive
queue (pFrom->vRecv) and if it finds one, it calls
ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv), which
is also in main.cpp.

Then the thread calls SendMessages for each node (which is in main.cpp)
which handles creating and sending any messages appropriate for that node.


-- Thread ThreadRPCServer in rpc.cpp --


This thread will be rather complicated in that it implements an
HTTP(S)+JSONRPC server using boost classes that are probably going
to be unfamiliar to most developers.

You will see lines like this:
    acceptor.set_option(boost::asio::ip::tcp::acceptor::reuse_address(true));

and this:
    boost::thread api_caller(ReadHTTP, boost::ref(stream), boost::ref(mapHeaders), boost::ref(strRequest));
    if (!api_caller.timed_join(boost::posix_time::seconds(GetArg("-rpctimeout", 30))))

It appears the code above is creating a thread in order to apply 30
second timeout to reading an HTTPrequest.  When HTTP requests are
read, they are parsed, and then a routine corresponding to the
request command name is called to handle the request. This happens
in a loop until shutdown.



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