iv_wait(3) ivykis programmer's manual iv_wait(3)NAME
IV_WAIT_INTEREST_INIT, iv_wait_interest_register, iv_wait_interest_reg‐
ister_spawn, iv_wait_interest_unregister, iv_wait_interest_kill -
ivykis wait4(2) wrapper
SYNOPSIS
#include <iv_wait.h>
struct iv_wait_interest {
pid_t pid;
void *cookie;
void (*handler)(void *cookie, int status,
const struct rusage *rusage);
};
void IV_WAIT_INTEREST_INIT(struct iv_wait_interest *this);
int iv_wait_interest_register(struct iv_wait_interest *this);
int iv_wait_interest_register_spawn(struct iv_wait_interest *this, void
(*fn)(void *), void *cookie);
void iv_wait_interest_unregister(struct iv_wait_interest *this);
int iv_wait_interest_kill(const struct iv_wait_interest *this, int
sig);
DESCRIPTION
iv_wait is an ivykis(3) wrapper around wait4(2), integrating process
state change notification with the ivykis event loop.
An ivykis application desiring process state change notifications reg‐
isters a struct iv_wait_interest object by calling iv_wait_inter‐
est_register, after having initialised it with IV_WAIT_INTEREST_INIT
and subsequently having filled in the ->pid, ->cookie and ->handler
members.
Alternatively, an ivykis application can use iv_wait_interest_regis‐
ter_spawn to atomically fork off a child process and register a struct
iv_wait_interest for it. In this context, 'atomically' means that the
call to iv_wait_interest_register_spawn will be serialised with respect
to invocations of wait4(2), which closes the race where process state
change notifications can occur and be delivered between forking off the
child process and registering a struct iv_wait_interest for the child's
pid. The child process will run the function given by the
iv_wait_interest_register_spawn argument fn, with argument cookie as
its argument.
Once a process state change occurs (as indicated by delivery of a
SIGCHLD signal to the current process), iv_wait calls wait4(2) to
return information about the process state change, looks up the
returned process ID in the set of registered struct iv_wait_interest
objects, and if there is a registered interest with a matching ->pid
field, arranges for that object's callback function to be called in the
thread that the object was registered in.
Process state change notifications will continue to be delivered to the
object's callback function until iv_wait_interest_unregister is called
on the object or until a WIFEXITED or WIFSIGNALED status for this pid
is returned by wait4(2).
Delivery of a WIFEXITED or WIFSIGNALED status does not automatically
unregister the object, this always needs to be done explicitly.
Unregistering a struct iv_wait_interest object can only be done from
the thread that that object was registered in, but within that thread,
can safely be done from (and its underlying memory allocation can
safely be freed from) its own callback function.
Registering multiple struct iv_wait_interest objects for the same
process ID will produce undefined behavior.
To send a signal to a child process, use iv_wait_interest_kill. This
function will internally serialise with invocations of wait4(2), to
avoid the race between sending a signal to a process and collecting a
termination notification for that process (which makes its pid avail‐
able for reuse).
Internally, iv_wait is implemented using iv_signal(3) and iv_event(3).
SEE ALSOivykis(3), iv_signal(3), iv_event(3), wait4(2)ivykis 2010-09-03 iv_wait(3)
