Multithreaded Programming Guide

Similar Solaris Threads Functions

Table 8–3 Similar Solaris Threads Functions


Operation	Destination Discussion
Create a thread	thr_create(3THR)
Get the minimal stack size	thr_min_stack(3THR)
Get the thread identifier	thr_self(3THR)
Yield thread execution	thr_yield(3THR)
Send a signal to a thread	thr_kill(3THR)
Access the signal mask of the calling thread	thr_sigsetmask(3THR)
Terminate a thread	thr_exit(3THR)
Wait for thread termination	thr_join(3THR)
Create a thread-specific data key	thr_keycreate(3THR)
Set thread-specific data	thr_setspecific(3THR)
Get thread-specific data	thr_getspecific(3THR)
Set the thread priority	thr_setprio(3THR)
Get the thread priority	thr_getprio(3THR)

Create a Thread

The thr_create(3THR) routine is one of the most elaborate of all the Solaris threads library routines.

thr_create(3THR)

Usethr_create(3THR) to add a new thread of control to the current process. (For POSIX threads, see pthread_create(3THR).)

Note that the new thread does not inherit pending signals, but it does inherit priority and signal masks.

#include <thread.h>

int thr_create(void *stack_base, size_t stack_size,
    void *(*start_routine) (void *), void *arg, long flags,
    thread_t *new_thread);

size_t thr_min_stack(void);

stack_base—Contains the address for the stack that the new thread uses. If stack_base is NULL then thr_create() allocates a stack for the new thread with at least stack_size bytes.

stack_size—Contains the size, in number of bytes, for the stack that the new thread uses. If stack_size is zero, a default size is used. In most cases, a zero value works best. If stack_size is not zero, it must be greater than the value returned by thr_min_stack().

There is no general need to allocate stack space for threads. The threads library allocates 1 megabyte of virtual memory for each thread's stack with no swap space reserved. (The library uses the -MAP_NORESERVE option of mmap(2) to make the allocations.)

start_routine—Contains the function with which the new thread begins execution. When start_routine() returns, the thread exits with the exit status set to the value returned by start_routine (see thr_exit(3THR)).

arg—Can be anything that is described by void, which is typically any 4-byte value. Anything larger must be passed indirectly by having the argument point to it.

Note that you can supply only one argument. To get your procedure to take multiple arguments, encode them as one (such as by putting them in a structure).

flags—Specifies attributes for the created thread. In most cases a zero value works best.

The value in flags is constructed from the bitwise inclusive OR of the following:

THR_SUSPENDED—Suspends the new thread and does not execute start_routine until the thread is started by thr_continue(). Use this to operate on the thread (such as changing its priority) before you run it. The termination of a detached thread is ignored.

THR_DETACHED—Detaches the new thread so that its thread ID and other resources can be reused as soon as the thread terminates. Set this when you do not want to wait for the thread to terminate.

Note –

When there is no explicit synchronization to prevent it, an unsuspended, detached thread can die and have its thread ID reassigned to another new thread before its creator returns from thr_create().

THR_BOUND—Permanently binds the new thread to an LWP (the new thread is a bound thread).

THR_DAEMON—Marks the new thread as a daemon. A daemon thread is always detached (THR_DAEMON implies THR_DETACHED). The process exits when all nondaemon threads exit. Daemon threads do not affect the process exit status and are ignored when counting the number of thread exits.

A process can exit either by calling exit() or by having every thread in the process that was not created with the THR_DAEMON flag call thr_exit(3THR). An application, or a library it calls, can create one or more threads that should be ignored (not counted) in the decision of whether to exit. The THR_DAEMON flag identifies threads that are not counted in the process exit criterion.

new_thread—Points to a location (when new_thread is not NULL) where the ID of the new thread is stored when thr_create() is successful. The caller is responsible for supplying the storage this argument points to. The ID is valid only within the calling process.

If you are not interested in this identifier, supply a NULL value to new_thread.

Return Values

thr_create() returns zero when it completes successfully. Any other return value indicates that an error occurred. When any of the following conditions is detected, thr_create() fails and returns the corresponding value.

EAGAIN: A system limit is exceeded, such as when too many LWPs have been created.

ENOMEM: Not enough memory was available to create the new thread.

EINVAL: stack_base is not NULL and stack_size is less than the value returned by thr_min_stack.()

Stack Behavior

Stack behavior in Solaris threads is generally the same as that in pthreads. For more information about stack setup and operation, see About Stacks.

You can get the absolute minimum on stack size by calling thr_min_stack(), which returns the amount of stack space required for a thread that executes a null procedure. Useful threads need more than this, so be very careful when reducing the stack size.

You can specify a custom stack in two ways. The first is to supply a NULL for the stack location, thereby asking the runtime library to allocate the space for the stack, but to supply the desired size in the stacksize parameter to thr_create().

The other approach is to take overall aspects of stack management and supply a pointer to the stack to thr_create(). This means that you are responsible not only for stack allocation but also for stack deallocation—when the thread terminates, you must arrange for the disposal of its stack.

When you allocate your own stack, be sure to append a red zone to its end by calling mprotect(2).

Get the Minimal Stack Size

thr_min_stack(3THR)

Use thr_min_stack(3THR) to get the minimum stack size for a thread.

#include <thread.h>

size_t thr_min_stack(void);

thr_min_stack() returns the amount of space needed to execute a null thread (a null thread is a thread that is created to execute a null procedure).

A thread that does more than execute a null procedure should allocate a stack size greater than the size of thr_min_stack().

When a thread is created with a user-supplied stack, the user must reserve enough space to run the thread. In a dynamically linked execution environment, it is difficult to know what the thread minimal stack requirements are.

Most users should not create threads with user-supplied stacks. User-supplied stacks exist only to support applications that require complete control over their execution environments.

Instead, users should let the threads library manage stack allocation. The threads library provides default stacks that should meet the requirements of any created thread.

Get the Thread Identifier

thr_self(3THR)

Use thr_self(3THR) to get the ID of the calling thread. (For POSIX threads, see pthread_self(3THR).)

#include <thread.h>

thread_t thr_self(void);

Yield Thread Execution

thr_yield(3THR)

thr_yield(3THR) causes the current thread to yield its execution in favor of another thread with the same or greater priority; otherwise it has no effect. There is no guarantee that a thread calling thr_yield() will do so.

#include <thread.h>

void thr_yield(void);

Send a Signal to a Thread

thr_kill(3THR)

thr_kill(3THR) sends a signal to a thread. (For POSIX threads, see pthread_kill(3THR).)

#include <thread.h>
#include <signal.h>
int thr_kill(thread_t target_thread, int sig);

Access the Signal Mask of the Calling Thread

thr_sigsetmask(3THR)

Use thr_sigsetmask(3THR) to change or examine the signal mask of the calling thread.

#include <thread.h>
#include <signal.h>
int thr_sigsetmask(int how, const sigset_t *set, sigset_t *oset);

Terminate a Thread

thr_exit(3THR)

Use thr_exit(3THR) to terminate a thread. (For POSIX threads, see pthread_exit(3THR).)

#include <thread.h>

void thr_exit(void *status);

Wait for Thread Termination

thr_join(3THR)

Use thr_join(3THR) to wait for a thread to terminate. (For POSIX threads, see pthread_join(3THR).)

#include <thread.h>

int thr_join(thread_t tid, thread_t *departedid, void **status);

Join specific

#include <thread.h>

thread_t tid;
thread_t departedid;
int ret;
void *status;

/* waiting to join thread "tid" with status */
ret = thr_join(tid, &departedid, &status);

/* waiting to join thread "tid" without status */
ret = thr_join(tid, &departedid, NULL);

/* waiting to join thread "tid" without return id and status */
ret = thr_join(tid, NULL, NULL);

When the tid is (thread_t)0, then thread_join() waits for any undetached thread in the process to terminate. In other words, when no thread identifier is specified, any undetached thread that exits causes thread_join() to return.

Join any

#include <thread.h>

thread_t tid;
thread_t departedid;
int ret;
void *status;

/* waiting to join any non-detached thread with status */
ret = thr_join(0, &departedid, &status);

By indicating 0 as the thread id in the Solaris thr_join(), a join will take place when any non detached thread in the process exits. The departedid will indicate the thread ID of the exiting thread.

Create a Thread-Specific Data Key

Except for the function names and arguments, thread specific data is the same for Solaris as it is for POSIX. The synopses for the Solaris functions are given in this section.

thr_keycreate(3THR)

thr_keycreate(3THR) allocates a key that is used to identify thread-specific data in a process. (For POSIX threads, see pthread_key_create(3THR).)

#include <thread.h>

int thr_keycreate(thread_key_t *keyp,
    void (*destructor) (void *value));

Set Thread-Specific Data

thr_setspecific(3THR)

thr_setspecific(3THR) binds value to the thread-specific data key, key, for the calling thread. (For POSIX threads, see pthread_setspecific(3THR).)

#include <thread.h>

int thr_setspecific(thread_key_t key, void *value);

Get Thread-Specific Data

thr_getspecific(3THR)

thr_getspecific(3THR) stores the current value bound to key for the calling thread into the location pointed to by valuep. (For POSIX threads, see pthread_getspecific(3THR).)

#include <thread.h>

int thr_getspecific(thread_key_t key, void **valuep);

Set the Thread Priority

In Solaris threads, if a thread is to be created with a priority other than that of its parent's, it is created in SUSPEND mode. While suspended, the threads priority is modified using the thr_setprio(3THR) function call; then it is continued.

A higher priority thread will receive precedence by libthread over lower priority threads with respect to synchronization object contention.

thr_setprio(3THR)

thr_setprio(3THR) changes the priority of the thread, specified by tid, within the current process to the priority specified by newprio. (For POSIX threads, see pthread_setschedparam(3THR).)

#include <thread.h>

int thr_setprio(thread_t tid, int newprio)

By default, threads are scheduled based on fixed priorities that range from zero, the least significant, to 127 the most significant.

thread_t tid;
int ret;
int newprio = 20;

/* suspended thread creation */
ret = thr_create(NULL, NULL, func, arg, THR_SUSPENDED, &tid);

/* set the new priority of suspended child thread */
ret = thr_setprio(tid, newprio);

/* suspended child thread starts executing with new priority */
ret = thr_continue(tid);

Get the Thread Priority

thr_getprio(3THR)

Use thr_getprio(3THR) to get the current priority for the thread. Each thread inherits a priority from its creator. thr_getprio() stores the current priority, tid, in the location pointed to by newprio. (For POSIX threads, see pthread_getschedparam(3THR).)

#include <thread.h>

int thr_getprio(thread_t tid, int *newprio)