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fork and fork bomb moved in from cpp-cheat

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Ciro Santilli 六四事件 法轮功
2019-11-12 00:00:00 +00:00
parent 762cd8d601
commit ca47a77676
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README.adoc
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@@ -13783,6 +13783,8 @@ This first allows memory overcommit so to that the program can mmap 1GiB, 4x mor
It then walks over every page and writes a value in it to ensure that it is used.
A <<fork-bomb>> is another example that can trigger the OOM killer.
Algorithm used by the OOM: https://unix.stackexchange.com/questions/153585/how-does-the-oom-killer-decide-which-process-to-kill-first
==== C multithreading
@@ -13875,9 +13877,47 @@ These links provide a clear overview of what POSIX is:
* link:userland/posix/count.c[] illustrates `sleep()`
* link:userland/posix/count_to.c[] minor variation of link:userland/posix/count.c[]
==== fork
POSIX' multiprocess API. Contrast with <<pthreads>> which are for threads.
Example: link:userland/posix/fork.c[]
Sample <<userland-setup-getting-started-natively,native userland output>> on Ubuntu 19.04 at 762cd8d601b7db06aa289c0fca7b40696299a868 + 1:
....
before fork before fork pid=13038 ppid=4805
after fork after fork pid=13038 ppid=4805
after (pid == 0) after (pid == 0) pid=13038 ppid=4805
after fork after fork pid=13039 ppid=13038
inside (pid == 0) inside (pid == 0) pid=13039 ppid=13038
after wait after wait pid=13038 ppid=4805
fork() return = 13039
....
Read the source comments and understand everything that is going on!
===== Fork bomb
https://en.wikipedia.org/wiki/Fork_bomb
DANGER! Only run this on your host if you have saved all data you care about! Better run it inside an emulator! QEMU v4.0.0 <<user-mode-simulation,user mode>> is not safe enough either because it is very native does not limit guest memory, so it will still blow up the host!
So without further ado, let's rock:
....
./run --eval-after './posix/fork_bomb.out danger'
....
Source: link:userland/posix/fork_bomb.c[]
Outcome on LKMC 762cd8d601b7db06aa289c0fca7b40696299a868 + 1: after a few seconds of an unresponsive shell, we get a visit form the <<linux-out-of-memory-killer>>, and the system is restored!
==== pthreads
POSIX' multithreading API. This was for a looong time the only "portable" multithreading alternative, until <<cpp-multithreading,C++11 finally added threads>>, thus also extending the portability to Windows.
POSIX' multithreading API. Contrast with <<fork>> which is for processes.
This was for a looong time the only "portable" multithreading alternative, until <<cpp-multithreading,C++11 finally added threads>>, thus also extending the portability to Windows.
* link:userland/posix/pthread_count.c[]
* link:userland/posix/pthread_deadlock.c[]