Differences between process and thread
- Process is independent executable with independent virtual memory and control flow
- Threads are part of processes
What does a mutex do
- control access to shared resource
- only thread that obtains mutex can access shared resource
What does a semaphore do
- variable, generalization of mutex
What are 4 things every process have
- PID (process ID)
- PPID (parent process ID)
- independent address space and virtual memory
- control flow
What does fork() do and return
- creates new process running two copies of the remaining code along with parent process
- child process returns 0
- parent process returns child PID
What do exec() family functions do
- runs another program with same PID
What does wait() do
- puts delay in parent process until a child process returns
- returns PID of child process that ended
What does system() do
- run specified command or program as shell command
- when called, process blocked until command is finished, then control is returned to process
What are the two main approaches to IPC?
- signals: int value sent from one process to another, can only be used on same host
- sockets: endpoints for sending or receiving data between processes
What does signal(SIGUSR1, sigHandler) do
- first parameter takes signal code
- second parameter is signal-handling function name
- signal handler functions are void with single int parameter
What does kill() function do
- first parameter is PID of target process
- second parameter is signal code
How to identify a process when using sockets
- IP address: unique to each host (computer) on the same network
- port number: unique identifier of processes on the host
What are the two main transport layers
- TCP (transport control protocol)
- UDP (user datagram protocol)
What are the 3 types of sockets and what transport layer do they work with
Stream socket: connection must be established then closed, best for reliable in-order delivery, TCP
Datagram socket: connectionless, data sent when ready, faster sending but no reliable order, UDP
Raw socket: bypass transport layer
What does the kernel do
- Intermediary between hardware and user programs
- Manages memory, execution of programs, communication w/ devices
- builds process table to keep track of processes
What are possible values for the second parameter of signal()
- SIG_IGN: ignore
- SIG_DFL: default handling
- Signal handler function: call this function
What is an orphan process
- a process where parent process terminated without terminating child
What is a zombie process
- a child process that has exited but is still in process table
- waiting for parent to look at its return value
What are the connection steps for a TCP server
- create stream socket
- bind socket to server’s IP address and port #
- listen on socket for incoming client connection requests
- accept client connection
- receive/send data
- close socket
What are the connection steps for a TCP client
- create stream socket
- connect to server at its IP address and port #
- send/receive data
- close socket
What’s the process for a UDP server
- create datagram socket where messages are received
- bind socket to server’s IP address and port #
- select incoming message from client
- receive/send data
- close socket
What’s the process for a TCP server
- create datagram socket to connect to server
- connect to server at its IP address and port #
- send/receive data
- close socket
What are thread contexts
- unique resources to each thread
includes: - unique thread ID
- unique function call stack
- program counter (keep track of current executing instruction)
What do threads share
- address space
- data segment
- code segment
