thr_new (2)

Leading comments

Copyright (c) 2016 The FreeBSD Foundation, Inc.
All rights reserved.

This documentation was written by
Konstantin Belousov <kib@FreeBSD.org> under sponsorship
from the FreeBSD Foundation.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form...

(The comments found at the beginning of the groff file "man2/thr_new.2freebsd".)

NAME

thr_new - create new thread of execution

LIBRARY

Lb libc

SYNOPSIS

In sys/thr.h Ft int Fn thr_new struct thr_param *param int param_size

DESCRIPTION

Bf -symbolic This function is intended for implementing threading. Normal applications should call pthread_create3 instead. Ef

The Fn thr_new system call creates a new kernel-scheduled thread of execution in the context of the current process. The newly created thread shares all attributes of the process with the existing kernel-scheduled threads in the process, but has private processor execution state. The machine context for the new thread is copied from the creating thread's context, including coprocessor state. FPU state and specific machine registers are excluded from the copy. These are set according to ABI requirements and syscall parameters. The FPU state for the new thread is reinitialized to clean.

The Fa param structure supplies parameters affecting the thread creation. The structure is defined in the In sys/thr.h header as follows

struct thr_param {
    void          (*start_func)(void *);
    void          *arg;
    char          *stack_base;
    size_t        stack_size;
    char          *tls_base;
    size_t        tls_size;
    long          *child_tid;
    long          *parent_tid;
    int           flags;
    struct rtprio *rtp;
};

and contains the following fields:

start_func

Pointer to the thread entry function. The kernel arranges for the new thread to start executing the function upon the first return to userspace.

arg

Opaque argument supplied to the entry function.

stack_base

Stack base address. The stack must be allocated by the caller. On some architectures, the ABI might require that the system put information on the stack to ensure the execution environment for start_func

stack_size

Stack size.

tls_base

TLS base address. The value of TLS base is loaded into the ABI-defined machine register in the new thread context.

tls_size

TLS size.

child_tid

Address to store the new thread identifier, for the child's use.

parent_tid

Address to store the new thread identifier, for the parent's use.

Both child_tid and parent_tid are provided, with the intent that child_tid is used by the new thread to get its thread identifier without issuing the thr_self2 syscall, while parent_tid is used by the thread creator. The latter is separate from child_tid because the new thread might exit and free its thread data before the parent has a chance to execute far enough to access it.

flags

Thread creation flags. The flags member may specify the following flags:

THR_SUSPENDED

Create the new thread in the suspended state. The flag is not currently implemented.

THR_SYSTEM_SCOPE

Create the system scope thread. The flag is not currently implemented.

rtp

Real-time scheduling priority for the new thread. May be NULL to inherit the priority from the creating thread.

The Fa param_size argument should be set to the size of the Fa param structure.

After the first successful creation of an additional thread, the process is marked by the kernel as multi-threaded. In particular, the P_HADTHREADS flag is set in the process' p_flag (visible in the ps(1) output), and several operations are executed in multi-threaded mode. For instance, the execve(2) system call terminates all threads but the calling one on successful execution.

RETURN VALUES

If successful, Fn thr_new will return zero, otherwise -1 is returned, and errno is set to indicate the error.

ERRORS

The Fn thr_new operation returns the following errors:

Bq Er EFAULT

The memory pointed to by the Fa param argument is not valid.

Bq Er EFAULT

The memory pointed to by the Fa param structure Fa child_tid , parent_tid or Fa rtp arguments is not valid.

Bq Er EFAULT

The specified stack base is invalid, or the kernel was unable to put required initial data on the stack.

Bq Er EINVAL

The Fa param_size argument specifies a negative value, or the value is greater than the largest Fa struct param size the kernel can interpret.

Bq Er EINVAL

The Fa rtp member is not NULL and specifies invalid scheduling parameters.

Bq Er EINVAL

The specified TLS base is invalid.

Bq Er EPERM

The caller does not have permission to set the scheduling parameters or scheduling policy.

Bq Er EPROCLIM

Creation of the new thread would exceed the RACCT_NTHR limit, see racct(2).

Bq Er EPROCLIM

Creation of the new thread would exceed the kern.threads.max_threads_per_proc sysctl(2) limit.

Bq Er ENOMEM

There was not enough kernel memory to allocate the new thread structures.

SEE ALSO

ps(1), execve(2), racct(2), thr_exit2, thr_kill2, thr_kill22, thr_self2, thr_set_name2, _umtx_op2, pthread_create3

STANDARDS

The Fn thr_new system call is non-standard and is used by the Lb libthr to implement St -p1003.1-2001 pthread(3) functionality.