kthread(9) - NetBSD Manual Pages

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KTHREAD(9)             NetBSD Kernel Developer's Manual             KTHREAD(9)


NAME

     kthread_create, 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_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_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 ALSO

     condvar(9), driver(9), softint(9), workqueue(9)


HISTORY

     The kthread framework appeared in NetBSD 1.4.

NetBSD 9.2                      April 21, 2015                      NetBSD 9.2