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				.\" 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.
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				.\" $FreeBSD$
				.\"
				.Dd May 5, 2016
				.Dt THR_NEW 2
				.Os
				.Sh NAME
				.Nm thr_new
				.Nd create new thread of execution
				.Sh LIBRARY
				.Lb libc
				.Sh SYNOPSIS
				.In sys/thr.h
				.Ft int
				.Fn thr_new "struct thr_param *param" "int param_size"
				.Sh DESCRIPTION
				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 new thread is reinitialized to clean.
				.Pp
				The
				.Fa param
				structure supplies parameters affecting the thread creation.
				The structure is defined in the
				.In sys/thr.h
				header as follows
				.Bd -literal
				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;
				};
				.Ed
				and contains the following fields:
				.Bl -tag -width ".Va parent_tid"
				.It Va start_func
				The pointer to the thread entry function.
				Kernel arranges for the new thread to start executing the function
				upon the first return to userspace.
				.It Va arg
				Opaque argument supplied to the entry function.
				.It Va stack_base
				Stack base address.
				The stack must be allocated by the caller.
				On some architectures, the ABI might require that system put information
				on the stack to ensure the execution environment for
				.Va start_func .
				.It Va stack_size
				Stack size.
				.It Va tls_base
				TLS base address.
				The value of TLS base is loaded to the ABI-defined machine register
				in the new thread context.
				.It Va tls_size
				TLS size.
				.It Va child_tid
				Address to store the new thread identifier, for the child's use.
				.It Va parent_tid
				Address to store the new thread identifier, for the parent's use.
				.Pp
				Both
				.Va child_tid
				and
				.Va parent_tid
				are provided, with the intent that
				.Va child_tid
				is used by the new thread to get its thread identifier without
				issuing the
				.Xr thr_self 2
				syscall, while
				.Va parent_tid
				is used by the thread creator.
				The later is separate from the
				.Va child_tid
				because new thread might exit and free its thread data before parent
				has a chance to execute far enough to access it.
				.It Va flags
				Thread creation flags.
				The
				.Va flags
				member may specify the following flags:
				.Bl -tag -width ".Dv THR_SYSTEM_SCOPE"
				.It Dv THR_SUSPENDED
				Create the new thread in the suspended state.
				The flag is not currently implemented.
				.It Dv THR_SYSTEM_SCOPE
				Create the system scope thread.
				The flag is not currently implemented.
				.El
				.It Va rtp
				Real-time scheduling priority for the new thread.
				May be NULL if thread should inherit the priority from the
				creating thread.
				.El
				.Pp
				The
				.Fa param_size
				argument should be set to the size of the
				.Fa param
				structure.
				.Pp
				After the first successful creation of an additional thread,
				the process is marked by the kernel as multi-threaded.
				In particular, the
				.Dv P_HADTHREADS
				flag is set in the process'
				.Dv p_flag
				(visible in the
				.Xr ps 1
				output), and several operations are executed in multi-threaded mode.
				For instance, the
				.Xr execve 2
				system call terminates all threads but the calling one on successful
				execution.
				.Sh RETURN VALUES
				If successful,
				.Fn thr_new
				will return zero, otherwise \-1 is returned, and
				.Va errno
				is set to indicate the error.
				.Sh ERRORS
				The
				.Fn thr_new
				operation returns the following errors:
				.Bl -tag -width Er
				.It Bq Er EFAULT
				The memory pointed to by the
				.Fa param
				argument is not valid.
				.It Bq Er EFAULT
				The memory pointed to by the
				.Fa param
				structure
				.Fa child_tid , parent_tid
				or
				.Fa rtp
				arguments is not valid.
				.It Bq Er EFAULT
				Specified stack base is invalid, or the kernel was unable to put required
				initial data on the stack.
				.It Bq Er EINVAL
				The
				.Fa param_size
				argument specifies negative value, or its value is greater than the
				largest
				.Fa struct param
				size the kernel can interpret.
				.It Bq Er EINVAL
				The
				.Fa rtp
				member is not NULL, but specifies invalid scheduling parameters.
				.It Bq Er EINVAL
				The specified TLS base is invalid.
				.It Bq Er EPROCLIM
				Creation of the new thread would exceed the
				.Dv RACCT_NTHR
				limit, see
				.Xr racct 2 .
				.It Bq Er EPROCLIM
				Creation of the new thread would exceed the
				.Dv kern.threads.max_threads_per_proc
				.Xr sysctl 2
				limit.
				.It Bq Er ENOMEM
				No kernel memory to allocate for the new thread structures.
				.El
				.Sh SEE ALSO
				.Xr ps 1 ,
				.Xr execve 2 ,
				.Xr racct 2 ,
				.Xr thr_exit 2 ,
				.Xr thr_kill 2 ,
				.Xr thr_kill2 2 ,
				.Xr thr_self 2 ,
				.Xr thr_set_name 2 ,
				.Xr _umtx_op 2
				.Sh STANDARDS
				The
				.Fn thr_new
				system call is non-standard and is used by the
				.Lb libthr
				to implement
				.St -p1003.1-2001
				.Xr pthread(3)
				functionality.