KTHREAD(9) BSD Kernel Developer's Manual KTHREAD(9)NAME
kthread_create, kthread_destroy, kthread_exit, kthread_join — kernel
threads
SYNOPSIS
#include <sys/kthread.h>
int
kthread_create(pri_t pri, int flags, struct cpu_info *ci,
void (*func)(void *), void *arg, lwp_t **newlp, const char *fmt,
...);
void
kthread_destroy(lwp_t *l);
void
kthread_exit(int ecode);
int
kthread_join(lwp_t *l);
DESCRIPTION
Kernel threads are light-weight processes which execute entirely within
the kernel.
Any process can request the creation of a new kernel thread. Kernel
threads are not swapped out during memory congestion. The VM space and
limits are shared with proc0 (usually swapper).
FUNCTIONS
kthread_create(pri, flags, ci, func, arg, newlp, fmt, ...)
Create a kernel thread. The arguments are as follows.
pri Priority level for the thread. If no priority level is
desired specify PRI_NONE, causing kthread_create() to
select the default priority level.
flags Flags that can be logically ORed together to alter the
thread's behaviour.
ci If non-NULL, the thread will be created bound to the
CPU specified by ci, meaning that it will only ever
execute on that CPU. By default, the threads are free
to execute on any CPU in the system.
func A function to be called when the thread begins execut‐
ing. This function must not return. If the thread
runs to completion, it must call kthread_exit() to
properly terminate itself.
arg An argument to be passed to func(). May be NULL if not
required.
newlp A pointer to receive the new LWP structure for the ker‐
nel thread. May be NULL, unless KTHREAD_MUSTJOIN is
specified in flags.
fmt A string containing format information used to display
the kernel thread name. Must not be NULL.
The following flags are defined.
KTHREAD_IDLE Causes the thread to be created in the LSIDL
(idle) state. By default, the threads are
created in the LSRUN (runnable) state, meaning
they will begin execution shortly after cre‐
ation.
KTHREAD_MPSAFE Specifies that the thread does its own locking
and so is multiprocessor safe. If not speci‐
fied, the global kernel lock will be held
whenever the thread is running (unless explic‐
itly dropped by the thread).
KTHREAD_INTR Specifies that the thread services device
interrupts. This flag is intended for kernel
internal use and should not normally be speci‐
fied.
KTHREAD_TS Causes the kthread to be created in the
SCHED_OTHER class (timeshared). The thread's
priority will be dynamically adjusted by the
scheduler. Increased activity by the kthread
will cause its priority to fall; decreased
activity will cause its priority to rise. By
default, kthreads are created in the SCHED_RR
class, with a fixed priority specified by pri.
Threads in the SCHED_RR class do not have
their priority dynamically adjusted by the
scheduler.
KTHREAD_MUSTJOIN Indicates that created kthread must be joined.
In such case kthread_exit() will wait until
kthread_join() will be called.
kthread_destroy(l)
From another thread executing in the kernel, cause a kthread to
exit. The kthread must be in the LSIDL (idle) state.
kthread_exit(ecode)
Exit from a kernel thread. Must only be called by a kernel
thread.
kthread_join(l)
Suspend execution of calling thread until the target kthread
terminates. Conceptually the function can be compared to the
user space pthread_join(3), however it must be called only once
for kernel thread which was created using the KTHREAD_MUSTJOIN
flag and would wait on kthread_exit.
RETURN VALUES
Upon successful completion, kthread_create() returns 0. Otherwise, the
following error values are returned:
[EAGAIN] The limit on the total number of system processes would be
exceeded.
[EAGAIN] The limit RLIMIT_NPROC on the total number of processes under
execution by this user id would be exceeded.
CODE REFERENCES
The kthread framework itself is implemented within the file
sys/kern/kern_kthread.c. Data structures and function prototypes for the
framework are located in sys/sys/kthread.h.
SEE ALSOcondvar(9), driver(9), softint(9), workqueue(9)HISTORY
The kthread framework appeared in NetBSD 1.4.
BSD August 7, 2011 BSD
