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| System Calls | _lwp_create(2) |
| | _lwp_create - create a new light-weight process |
SYNOPSIS
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#include <sys/lwp.h> int _lwp_create(ucontext_t *contextp, uint_t flags, lwpid_t *new_lwp); |
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The _lwp_create() function adds a lightweight process (LWP) to the current process. The contextp argument specifies the initial signal mask, stack, and machine context (including the program counter and stack pointer) for the new LWP. The new LWP inherits the
scheduling class and priority of the caller.
If _lwp_create() is successful and new_lwp is not NULL, the ID of the new LWP is stored in the location pointed to by new_lwp.
The flags argument specifies additional attributes for the new LWP. The value in flags is constructed by the bitwise inclusive OR operation of the following values:
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LWP_DETACHED
- The LWP is created detached.
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LWP_DAEMON
- The LWP is created as a daemon LWP.
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LWP_SUSPENDED
- The LWP is created suspended.
If LWP_DETACHED or LWP_DAEMON is specified, then the LWP is created in the detached state. Otherwise the LWP is created in the undetached state. The ID (and system resources) associated with a detached
LWP can be automatically reclaimed when the LWP exits. The ID of an undetached LWP cannot be reclaimed until it exits and another LWP has reported its termination by way of _lwp_wait(2).
This allows the waiting LWP to determine that the waited for LWP has terminated and to reclaim any process resources that it was using.
If LWP_DAEMON is specified, then in addition to being created in the detached state, the LWP is created as a daemon LWP. Daemon LWPs do not interfere with the exit conditions for a process. A process will exit as though _exit(0) had been called when the last
non-daemon LWP calls _lwp_exit() (see exit(2) and _lwp_exit(2)).
Also, an LWP that is waiting in _lwp_wait(2) for any LWP to terminate will return EDEADLK when all remaining LWPs in the process are either daemon LWPs or other LWPs
waiting in _lwp_wait().
If LWP_SUSPENDED is specified, then the LWP is created in a suspended state. This allows the creator to change the LWP's inherited attributes before it starts to execute. The suspended LWP can only be resumed by way of _lwp_continue(2). If LWP_SUSPENDED is not specified the LWP can begin to run immediately after it has been created.
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Upon successful completion, 0 is returned. A non-zero value indicates an error.
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If any of the following conditions are detected, _lwp_create() fails and returns the corresponding value:
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EFAULT
- Either the context parameter or the new_lwp parameter point to invalid addresses.
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EAGAIN
- A system limit is exceeded, (for example, too many LWPs were created for this real user ID).
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EINVAL
- The flags argument contains values other than those specified above.
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| | Example 1. How a stack is allocated to a new LWP.
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This example shows how a stack is allocated to a new LWP. The _lwp_makecontext() function is used to set up the context parameter so that the new LWP begins executing a function.
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contextp = (ucontext_t *)malloc(sizeof(ucontext_t));
stackbase = malloc(stacksize);
_lwp_makecontext(contextp, func, arg, private, stackbase, stacksize);
sigprocmask(SIGSETMASK, NULL, &contextp->uc_sigmask);
error = _lwp_create(contextp, NULL, &new_lwp);
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Applications should use bound threads rather than the _lwp_* functions (see thr_create(3THR)). Using LWPs directly is not advised
because libraries are only safe to use with threads, not LWPs.
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See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Async-Signal-Safe |
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_lwp_cond_timedwait(2), _lwp_continue(2), _lwp_detach(2), _lwp_exit(2), _lwp_makecontext(2), _lwp_wait(2), alarm(2), exit(2), poll(2), signal(3HEAD), sleep(3C), thr_create(3THR), ucontext(3HEAD), attributes(5)
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