Tribblix: manual page: thr

THR_CREATE(3C) Standard C Library Functions THR_CREATE(3C)

NAME

thr_create - create a thread

SYNOPSIS

cc -mt [ flag... ] file...[ library... ]
#include <thread.h>

int thr_create(void *stack_base, size_t stack_size,
void *(*start_func) (void*), void *arg, long flags,
thread_t *new_thread_ID);

DESCRIPTION

Thread creation adds a new thread of control to the current process.
The procedure main() is a single thread of control. Each thread
executes concurrently with all other threads within the calling
process and with other threads from other active processes.

Although a newly created thread shares all of the calling process's
global data with the other threads in the process, it has its own set
of attributes and private execution stack. The new thread inherits
the calling thread's signal mask and scheduling priority. Pending
signals for a new thread are not inherited and will be empty.

The call to create a thread takes the address of a user-defined
function, specified by start_func, as one of its arguments. This
function is the complete execution routine for the new thread.

The lifetime of a thread begins with the successful return from
thr_create(), which calls start_func() and ends with one of the
following:

o the normal completion of start_func(),

o an explicit call to thr_exit(3C), or

o the conclusion of the calling process (see exit(2)).

The new thread performs by calling the function defined by start_func
with only one argument, arg. If more than one argument needs to be
passed to start_func, the arguments can be packed into a structure,
the address of which can be passed to arg.

If start_func returns, the thread terminates with the exit status set
to the start_func return value (see thr_exit(3C)).

When the thread from which main() originated returns, the effect is
the same as if an implicit call to exit() were made using the return
value of main() as the exit status. This behavior differs from a
start_func return. If main() calls thr_exit(3C), only the main
thread exits, not the entire process.

If the thread creation fails, a new thread is not created and the
contents of the location referenced by the pointer to the new thread
are undefined.

The flags argument specifies which attributes are modifiable for the
created thread. The value in flags is determined by the bitwise
inclusive-OR of the following:

THR_BOUND
This flag is obsolete and is maintained for
compatibility.

THR_DETACHED
This flag affects the detachstate attribute of the
thread. The new thread is created detached. The
exit status of a detached thread is not accessible
to other threads. Its thread ID and other resources
may be re-used as soon as the thread terminates.
thr_join(3C) will not wait for a detached thread.

THR_NEW_LWP
This flag is obsolete and is maintained for
compatibility.

THR_SUSPENDED
This flag affects the suspended attribute of the
thread. The new thread is created suspended and
will not execute start_func until it is started by
thr_continue().

THR_DAEMON
This flag affects the daemon attribute of the
thread. In addition to being created detached
(THR_DAEMON implies THR_DETACHED), the thread is
marked as a daemon. Daemon threads do not interfere
with the exit conditions for a process. A process
will terminate when the last non-daemon thread
exits or the process calls exit(2). Also, a thread
that is waiting in thr_join(3C) for any thread to
terminate will return EDEADLK when all remaining
threads in the process are either daemon threads or
other threads waiting in thr_join(). Daemon threads
are most useful in libraries that want to use
threads.

Default thread creation:

thread_t tid;
void *start_func(void *), *arg;
thr_create(NULL, 0, start_func, arg, 0, &tid);

Create a detached thread whose thread ID we do not care about:

thr_create(NULL, 0, start_func, arg, THR_DETACHED, NULL);

If stack_base is not NULL, the new thread uses the stack beginning at
the address specified by stack_base and continuing for stack_size
bytes, where stack_size must be greater than or equal to
THR_MIN_STACK. If stack_base is NULL, thr_create() allocates a stack
for the new thread with at least stack_size bytes. If stack_size is
0, a default size is used. If stack_size is not 0, it must be greater
than or equal to THR_MIN_STACK. See NOTES.

When new_thread_ID is not NULL, it points to a location where the ID
of the new thread is stored if thr_create() is successful. The ID is
only valid within the calling process.

RETURN VALUES

If successful, the thr_create() function returns 0. Otherwise, an
error value is returned to indicate the error.

ERRORS

EAGAIN
A resource control limit on the total number of threads in
a process, task, project, or zone has been exceeded or
some system resource has been exceeded.

EINVAL
The stack_base argument is not NULL and stack_size is less
than THR_MIN_STACK, or the stack_base argument is NULL and
stack_size is not 0 and is less than THR_MIN_STACK.

ENOMEM
The system cannot allocate stack for the thread.

The thr_create() function may use mmap() to allocate thread stacks
from MAP_PRIVATE, MAP_NORESERVE, and MAP_ANON memory mappings if
stack_base is NULL, and consequently may return upon failure the
relevant error values returned by mmap(). See the mmap(2) manual page
for these error values.

EXAMPLES

The following is an example of concurrency with multithreading. Since
POSIX threads and Solaris threads are fully compatible even within
the same process, this example uses pthread_create() if you execute
a.out 0, or thr_create() if you execute a.out 1.

Five threads are created that simultaneously perform a time-consuming
function, sleep(10). If the execution of this process is timed, the
results will show that all five individual calls to sleep for ten-
seconds completed in about ten seconds, even on a uniprocessor. If a
single-threaded process calls sleep(10) five times, the execution
time will be about 50-seconds.

The command-line to time this process is:

/usr/bin/time a.out 0 (for POSIX threading)

or

/usr/bin/time a.out 1 (for Solaris threading)

Example 1: An example of concurrency with multithreading.

#define _REENTRANT /* basic 3-lines for threads */
#include <pthread.h>
#include <thread.h>
#define NUM_THREADS 5
#define SLEEP_TIME 10

void *sleeping(void *); /* thread routine */
int i;
thread_t tid[NUM_THREADS]; /* array of thread IDs */

int
main(int argc, char *argv[])
{
if (argc == 1) {
printf("use 0 as arg1 to use pthread_create()\n");
printf("or use 1 as arg1 to use thr_create()\n");
return (1);
}

switch (*argv[1]) {
case '0': /* POSIX */
for ( i = 0; i < NUM_THREADS; i++)
pthread_create(&tid[i], NULL, sleeping,
(void *)SLEEP_TIME);
for ( i = 0; i < NUM_THREADS; i++)
pthread_join(tid[i], NULL);
break;

case '1': /* Solaris */
for ( i = 0; i < NUM_THREADS; i++)
thr_create(NULL, 0, sleeping, (void *)SLEEP_TIME, 0,
&tid[i]);
while (thr_join(0, NULL, NULL) == 0)
continue;
break;
} /* switch */
printf("main() reporting that all %d threads have
terminated\n", i);
return (0);
} /* main */

void *
sleeping(void *arg)
{
int sleep_time = (int)arg;
printf("thread %d sleeping %d seconds ...\n", thr_self(),
sleep_time);
sleep(sleep_time);
printf("\nthread %d awakening\n", thr_self());
return (NULL);
}

Had main() not waited for the completion of the other threads (using
pthread_join(3C) or thr_join(3C)), it would have continued to process
concurrently until it reached the end of its routine and the entire
process would have exited prematurely (see exit(2)).

Example 2: Creating a default thread with a new signal mask.

The following example demonstrates how to create a default thread
with a new signal mask. The new_mask argument is assumed to have a
value different from the creator's signal mask (orig_mask). The
new_mask argument is set to block all signals except for SIGINT. The
creator's signal mask is changed so that the new thread inherits a
different mask, and is restored to its original value after
thr_create() returns.

This example assumes that SIGINT is also unmasked in the creator.
If it is masked by the creator, then unmasking the signal opens the
creator to this signal. The other alternative is to have the new
thread set its own signal mask in its start routine.

thread_t tid;
sigset_t new_mask, orig_mask;
int error;

(void)sigfillset(&new_mask);
(void)sigdelset(&new_mask, SIGINT);
(void)thr_sigsetmask(SIG_SETMASK, &new_mask, &orig_mask);
error = thr_create(NULL, 0, do_func, NULL, 0, &tid);
(void)thr_sigsetmask(SIG_SETMASK, &orig_mask, NULL);

ATTRIBUTES

NOTES

Since multithreaded-application threads execute independently of each
other, their relative behavior is unpredictable. It is therefore
possible for the thread executing main() to finish before all other
user-application threads.

Using thr_join(3C) in the following syntax,

while (thr_join(0, NULL, NULL) == 0)
continue;

will cause the invoking thread (which may be main()) to wait for the
termination of all non-daemon threads, excluding threads that are
themselves waiting in thr_join(); however, the second and third
arguments to thr_join() need not necessarily be NULL.

A thread has not terminated until thr_exit() has finished. The only
way to determine this is by thr_join(). When thr_join() returns a
departed thread, it means that this thread has terminated and its
resources are reclaimable. For instance, if a user specified a stack
to thr_create(), this stack can only be reclaimed after thr_join()
has reported this thread as a departed thread. It is not possible
to determine when a detached thread has terminated. A detached
thread disappears without leaving a trace.

Typically, thread stacks allocated by thr_create() begin on page
boundaries and any specified (a red-zone) size is rounded up to the
next page boundary. A page with no access permission is appended to
the top of the stack so that most stack overflows will result in a
SIGSEGV signal being sent to the offending thread. Thread stacks
allocated by the caller are used as is.

Using a default stack size for the new thread, instead of passing a
user-specified stack size, results in much better thr_create()
performance. The default stack size for a user-thread is 1 megabyte
in a 32-bit process and 2 megabyte in a 64-bit process.

A user-specified stack size must be greater than or equal to
THR_MIN_STACK. A minimum stack size may not accommodate the stack
frame for the user thread function start_func. If a stack size is
specified, it must accommodate start_func requirements and the
functions that it may call in turn, in addition to the minimum
requirement.

It is usually very difficult to determine the runtime stack
requirements for a thread. THR_MIN_STACK specifies how much stack
storage is required to execute a trivial start_func. The total
runtime requirements for stack storage are dependent on the storage
required to do runtime linking, the amount of storage required by
library runtimes (like printf()) that your thread calls. Since these
storage parameters are not known before the program runs, it is best
to use default stacks. If you know your runtime requirements or
decide to use stacks that are larger than the default, then it makes
sense to specify your own stacks.

March 16, 2009 THR_CREATE(3C)