THR_NEW(2) FreeBSD System Calls Manual THR_NEW(2)
NAME
thr_new - create new thread of execution
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/thr.h>
int
thr_new(struct thr_param *param, int param_size);
DESCRIPTION
This function is intended for implementing threading. Normal
applications should call pthread_create(3) instead.
The 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 param structure supplies parameters affecting the thread creation.
The structure is defined in the <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_self(2) 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.
THR_C_RUNTIME Indicate that the new thread is created by
the C language runtime. It has
architecture-specific meaning.
On amd64, the flag requests that the
specified tls_base was loaded into the
%fsbase register before calling a signal
handler.
rtp Real-time scheduling priority for the new thread. May be
NULL to inherit the priority from the creating thread.
The param_size argument should be set to the size of the 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, thr_new() will return zero, otherwise -1 is returned, and
errno is set to indicate the error.
ERRORS
The thr_new() operation returns the following errors:
[EFAULT] The memory pointed to by the param argument is not
valid.
[EFAULT] The memory pointed to by the param structure
child_tid, parent_tid or rtp arguments is not valid.
[EFAULT] The specified stack base is invalid, or the kernel was
unable to put required initial data on the stack.
[EINVAL] The param_size argument specifies a negative value, or
the value is greater than the largest struct param
size the kernel can interpret.
[EINVAL] The rtp member is not NULL and specifies invalid
scheduling parameters.
[EINVAL] The specified TLS base is invalid.
[EPERM] The caller does not have permission to set the
scheduling parameters or scheduling policy.
[EPROCLIM] Creation of the new thread would exceed the RACCT_NTHR
limit, see rctl_get_racct(2).
[EPROCLIM] Creation of the new thread would exceed the
kern.threads.max_threads_per_proc sysctl(3) limit.
[ENOMEM] There was not enough kernel memory to allocate the new
thread structures.
SEE ALSO
ps(1), _umtx_op(2), execve(2), rctl_get_racct(2), thr_exit(2),
thr_kill(2), thr_kill2(2), thr_self(2), thr_set_name(2),
pthread_create(3)
STANDARDS
The thr_new() system call is non-standard and is used by the Threading
Library (libthr, -lthr) to implement IEEE Std 1003.1-2001 ("POSIX.1")
pthread(3) functionality.
HISTORY
The thr_new() system call first appeared in FreeBSD 5.2.
FreeBSD 15.1-STABLE-HBSD May 5, 2020 THR_NEW(2)