In this network programming homework, we are asked to build a remote working ground (RWG), which is actually a combination of hw1 and chat & public pipe function.

According to the spec(hw2Spec.txt), we need to write two programs:

  1. Use the single-process concurrent paradigm.
  2. Use the concurrent connection-oriented paradigm with shared memory.

For more details, please refer to hw2Spec.txt in the repository (cyhuang1230/NetworkProgramming).

There are some notable ideas I came up with and described as follows.
(I will start with version II since I wrote that first :P)

For concurrent version:

  • Keep track of client’s data (e.g. sockfd, pid…) so that we can send msg to each client.
  • Store client data & messages in shared memory so let every child can read.
  • Create additional MAX_USER(# of user) blocks of shm to store direct msg (or broadcst msg).
  • There’s no way server can be closed properly (must end by Ctrl+C), so, in order not to leave any shm unrelaesed, we won’t shmget until the first client is connected, and free shm when all clients are disconnected.
    → To keep track of the number of children, sa_handler needs to be implemented separately.
    → Furthermore, MUST reset sa_handler in the child process so that won’t mistakenly detach shm later when exec.
  • Use signal SIGUSR1 to notify other process there’s a new msg to write.
  • Semaphore on public pipes to prevent concurrent issue. (Same create/release idea as shm.)
  • Use FIFO, a.k.a Named pipe, to implement public pipe. [No need to store in shm].
  • Implement a generic function to send msg to a specific user.
    Function hierarchy:
    → sendRawMsgToClient → tell
    → sendRawMsgToClient → broadcastRawMsg → yell/name/who

For single-process version:

  • Basically same structure as ver. II, but as a single-process program, we don’t need any shm or semaphore, which makes it much easier, yayyy!.
  • Only involves one huge adjustment.
    Consider the following input:
[Client 1] % ls |1
[Client 2] % ls |1
[Client 1] % cat
[Client 2] (empty) <- stucked, prompt won't display

    This error is caused by the way we decide input.
    → We can no longer expect the whole input with numbered-pipe can be got in one while loop.
    → Instead, we have to check input line by line, and keep track of input-related information.

Demo video: (client is not included in the repo)
np_hw2_demo

Source → cyhuang1230/NetworkProgramming

For ver. I (Single process):
Please look for NP_project2_Single.cpp.
To try: make hw2s and run ./np_hw2s.
*Try with debug message: make hw2_debugs and run ./np_hw2s.

For ver. II (Concurrent):
Please look for NP_project2_Concurrent.cpp.
To try: make hw2 and run ./np_hw2.
*Try with debug message: make hw2_debug and run ./np_hw2.

*Debug version is complied with -g, which may use gdb np_hw2(s) to debug.