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libposix: document timers

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This commit is contained in:
Giacomo Tesio 2017-05-08 23:46:19 +02:00
parent a3791c88f7
commit aa4172a1de
1 changed files with 25 additions and 6 deletions
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31
sys/src/lib/posix/signals.c
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@ -23,8 +23,8 @@
* SIGABRT, SIGIOT), SIGCHLD/SIGCLD, timers' wakeups
* (SIGALRM, SIGPROF, SIGVTALRM) and all the others.
*
* # TRASMISSION
*
* TRASMISSION
* -----------
* Signal transmission depends on the relation between the sender
* and the receiver:
* 1) if sender and receiver have no relation the signal is translated
@ -48,8 +48,8 @@
* registered with signal() handled the signal and the library will
* invoke the default disposition associated to the signal.
*
* # CONTROL MESSAGES
*
* CONTROL MESSAGES
* ----------------
* Control messages are translated by the receiver to equivalent actions:
* - SIGKILL => write "kill" to the control file of the current process
* - SIGSTOP => write "stop" to the control file of the current process
@ -61,8 +61,8 @@
* "start" to the control file of the receiver before
* sending the note (unless SIGCHLD emulation is enable).
*
* # SIGCHLD/SIGCLD
*
* SIGCHLD/SIGCLD
* --------------
* Jehanne (like Plan 9) does not support a SIGCHLD equivalent.
* The user space emulation provided here is quite expensive, so it's
* disabled by default.
@ -95,6 +95,25 @@
* for forked children in the same way, sending them to P2C.
* It's P2C's responsibility to translate control messages as required,
* so that SIGCONT will work as expected.
*
* TIMERS
* ------
* The functions alarm() and settimer() generate SIGALRM, SIGPROF
* or SIGVTALRM for the current process. We want timers to be able to
* expire in a signal handler (interrupting a blocking syscall) but
* without giving up the simplicity of notes.
*
* We allocate these timers on libposix initialization. When normal
* code is running timers will be implemented via Jehanne's alarms,
* producing a note on expiration that will be mapped to the proper
* signal for the trampoline by the receiving process.
*
* However, when a signal handler is being executed, the timers will
* be implemented using the awake syscall that will be able
* to interrupt blocking syscalls in the signal handler.
* When a signal handler returns, if the timer has not be cleared and
* did not expired, the wakeup is cleared and replaced with an alarm
* note.
*/
#include <u.h>