порождать процесс (РАСШИРЕННОЕ РЕАЛЬНОЕ ВРЕМЯ) (spawn a process (ADVANCED REALTIME))
Описание (Description)
The posix_spawn() and posix_spawnp() functions shall create a new
process (child process) from the specified process image. The new
process image shall be constructed from a regular executable file
called the new process image file.
When a C program is executed as the result of this call, it shall
be entered as a C-language function call as follows:
int main(int argc, char *argv[]);
where argc is the argument count and argv is an array of
character pointers to the arguments themselves. In addition, the
following variable:
extern char **environ;
shall be initialized as a pointer to an array of character
pointers to the environment strings.
The argument argv is an array of character pointers to null-
terminated strings. The last member of this array shall be a null
pointer and is not counted in argc. These strings constitute the
argument list available to the new process image. The value in
argv[0] should point to a filename string that is associated with
the process image being started by the posix_spawn() or
posix_spawnp() function.
The argument envp is an array of character pointers to null-
terminated strings. These strings constitute the environment for
the new process image. The environment array is terminated by a
null pointer.
The number of bytes available for the combined argument and
environment lists of the child process is {ARG_MAX}. The
implementation shall specify in the system documentation (see the
Base Definitions volume of POSIX.1‐2017, Chapter 2, Conformance)
whether any list overhead, such as length words, null
terminators, pointers, or alignment bytes, is included in this
total.
The path argument to posix_spawn() is a pathname that identifies
the new process image file to execute.
The file parameter to posix_spawnp() shall be used to construct a
pathname that identifies the new process image file. If the file
parameter contains a <slash> character, the file parameter shall
be used as the pathname for the new process image file.
Otherwise, the path prefix for this file shall be obtained by a
search of the directories passed as the environment variable PATH
(see the Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables). If this environment variable is not
defined, the results of the search are implementation-defined.
If file_actions is a null pointer, then file descriptors open in
the calling process shall remain open in the child process,
except for those whose close-on-exec flag FD_CLOEXEC is set (see
fcntl(3p)). For those file descriptors that remain open, the
child process shall not inherit any file locks, but all remaining
attributes of the corresponding open file descriptions (see
fcntl(3p)), shall remain unchanged.
If file_actions is not NULL, then the file descriptors open in
the child process shall be those open in the calling process as
modified by the spawn file actions object pointed to by
file_actions and the FD_CLOEXEC flag of each remaining open file
descriptor after the spawn file actions have been processed. The
effective order of processing the spawn file actions shall be:
1. The set of open file descriptors for the child process shall
initially be the same set as is open for the calling process.
The child process shall not inherit any file locks, but all
remaining attributes of the corresponding open file
descriptions (see fcntl(3p)), shall remain unchanged.
2. The signal mask, signal default actions, and the effective
user and group IDs for the child process shall be changed as
specified in the attributes object referenced by attrp.
3. The file actions specified by the spawn file actions object
shall be performed in the order in which they were added to
the spawn file actions object.
4. Any file descriptor that has its FD_CLOEXEC flag set (see
fcntl(3p)) shall be closed.
If file descriptor 0, 1, or 2 would otherwise be closed in the
new process image created by posix_spawn() or posix_spawnp(),
implementations may open an unspecified file for the file
descriptor in the new process image. If a standard utility or a
conforming application is executed with file descriptor 0 not
open for reading or with file descriptor 1 or 2 not open for
writing, the environment in which the utility or application is
executed shall be deemed non-conforming, and consequently the
utility or application might not behave as described in this
standard.
The posix_spawnattr_t spawn attributes object type is defined in
<spawn.h>. It shall contain at least the attributes defined
below.
If the POSIX_SPAWN_SETPGROUP flag is set in the spawn-flags
attribute of the object referenced by attrp, and the spawn-pgroup
attribute of the same object is non-zero, then the child's
process group shall be as specified in the spawn-pgroup attribute
of the object referenced by attrp.
As a special case, if the POSIX_SPAWN_SETPGROUP flag is set in
the spawn-flags attribute of the object referenced by attrp, and
the spawn-pgroup attribute of the same object is set to zero,
then the child shall be in a new process group with a process
group ID equal to its process ID.
If the POSIX_SPAWN_SETPGROUP flag is not set in the spawn-flags
attribute of the object referenced by attrp, the new child
process shall inherit the parent's process group.
If the POSIX_SPAWN_SETSCHEDPARAM flag is set in the spawn-flags
attribute of the object referenced by attrp, but
POSIX_SPAWN_SETSCHEDULER is not set, the new process image shall
initially have the scheduling policy of the calling process with
the scheduling parameters specified in the spawn-schedparam
attribute of the object referenced by attrp.
If the POSIX_SPAWN_SETSCHEDULER flag is set in the spawn-flags
attribute of the object referenced by attrp (regardless of the
setting of the POSIX_SPAWN_SETSCHEDPARAM flag), the new process
image shall initially have the scheduling policy specified in the
spawn-schedpolicy attribute of the object referenced by attrp and
the scheduling parameters specified in the spawn-schedparam
attribute of the same object.
The POSIX_SPAWN_RESETIDS flag in the spawn-flags attribute of the
object referenced by attrp governs the effective user ID of the
child process. If this flag is not set, the child process shall
inherit the effective user ID of the parent process. If this flag
is set, the effective user ID of the child process shall be reset
to the parent's real user ID. In either case, if the set-user-ID
mode bit of the new process image file is set, the effective user
ID of the child process shall become that file's owner ID before
the new process image begins execution.
The POSIX_SPAWN_RESETIDS flag in the spawn-flags attribute of the
object referenced by attrp also governs the effective group ID of
the child process. If this flag is not set, the child process
shall inherit the effective group ID of the parent process. If
this flag is set, the effective group ID of the child process
shall be reset to the parent's real group ID. In either case, if
the set-group-ID mode bit of the new process image file is set,
the effective group ID of the child process shall become that
file's group ID before the new process image begins execution.
If the POSIX_SPAWN_SETSIGMASK flag is set in the spawn-flags
attribute of the object referenced by attrp, the child process
shall initially have the signal mask specified in the spawn-
sigmask attribute of the object referenced by attrp.
If the POSIX_SPAWN_SETSIGDEF flag is set in the spawn-flags
attribute of the object referenced by attrp, the signals
specified in the spawn-sigdefault attribute of the same object
shall be set to their default actions in the child process.
Signals set to the default action in the parent process shall be
set to the default action in the child process.
Signals set to be caught by the calling process shall be set to
the default action in the child process.
Except for SIGCHLD, signals set to be ignored by the calling
process image shall be set to be ignored by the child process,
unless otherwise specified by the POSIX_SPAWN_SETSIGDEF flag
being set in the spawn-flags attribute of the object referenced
by attrp and the signals being indicated in the spawn-sigdefault
attribute of the object referenced by attrp.
If the SIGCHLD signal is set to be ignored by the calling
process, it is unspecified whether the SIGCHLD signal is set to
be ignored or to the default action in the child process, unless
otherwise specified by the POSIX_SPAWN_SETSIGDEF flag being set
in the spawn_flags attribute of the object referenced by attrp
and the SIGCHLD signal being indicated in the spawn_sigdefault
attribute of the object referenced by attrp.
If the value of the attrp pointer is NULL, then the default
values are used.
All process attributes, other than those influenced by the
attributes set in the object referenced by attrp as specified
above or by the file descriptor manipulations specified in
file_actions, shall appear in the new process image as though
fork() had been called to create a child process and then a
member of the exec family of functions had been called by the
child process to execute the new process image.
It is implementation-defined whether the fork handlers are run
when posix_spawn() or posix_spawnp() is called.
