nQuant c++IV #1 #socket/thread

Overall, I remember nQuant IV was rather low-level and heavy on optimization. Mostly QQ.

Q: what’s offered on Layer 2? Can IP simply operate on top of physical layer without Layer 2?
A: ethernet is a L2 technology.
A: Each device on a network has a hardware address or MAC address, used by the data link layer

Q: when a user land thread makes a syscall, what’s the implication?
%%A: the thread enters kernel mode?

Q6: how could do you implement a userland thread?
%%A: setjump and longjmp

Q6b: how? I feel better be modest and offer my tentative guesses.

Q6c: how is setjump different from goto?
AA: http://ecomputernotes.com/what-is-c/function-a-pointer/what-is-the-difference-between-goto-and-longjmp-and-setjmp and http://www.geekinterview.com/question_details/3330

Q: by default, is a linux mutex cross-process?
%%A: the mutex in pthreads by default isn’t. Outside linux, the windows mutex is cross-process.
AA: Beyond the default, linux mutex can be cross-process — http://stackoverflow.com/questions/9389730/is-it-possible-to-use-mutex-in-multiprocessing-case-on-linux-unix

Q: in linux, what’s the difference between a process and a thread?

Q: start 5 copies of the current process, using fork? (Can use the example in [[head first c]] )

Q: If a variable in (2-process) shared memory is marked volatile, is it a reasonable usage of volatile keyword?
AA: now i think so. http://embeddedgurus.com/barr-code/2012/01/combining-cs-volatile-and-const-keywords/ shows use of “const volatile” on a variable in shared memory.
AA: [[moving from c to c++]] section on Volatile (P75) seems to agree

Q: what’s a limitation of the select() system call when there are too many sockets to check, and each messages (~ 2KB) is important.
A: select has max socket count. Use epoll() — http://stackoverflow.com/questions/5357445/select-max-sockets

Q: how many sockets can a single process open? Not too sure. A few hundred?
A: http://stackoverflow.com/questions/410616/increasing-the-maximum-number-of-tcp-ip-connections-in-linux

Q: what’s inside a socket? My socket book has detailed diagrams.
%%A: http://bigblog.tanbin.com/2011/06/5-parts-in-socket-object.html

Q: can a socket be shared by 2 processes?
AA: Yes. See https://bintanvictor.wordpress.com/2017/04/29/socket-shared-between-2-processes/

Q: what linux command to monitor network performance?
%%A: Beside netstat, I have seen tools that report error rates that indicate saturation
A: ss

Q: what linux command to monitor memory usage by a given process, showing size of heap, stack, text, even broken down to shared lib vs static lib
A: cat /proc/{pid}/smaps
A: pmap -x {pid}

Q: given a one-line c program “while(1);”, launch it and /usr/bin/top would show 100% cpu usage. What does it mean?

Q: how to remove the word “option” from a resume, unless it is a sub-word? Use perl or python
%%A: Word boundary symbol?

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