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.Dd January 20, 2006 .Dt _LWP_PARK 2 .Os .Sh NAME .Nm _lwp_park .Nd wait interruptably in the kernel .Sh LIBRARY .Lb libc .Sh SYNOPSIS n lwp.h .Ft int .Fn _lwp_park "const struct timespec *abstime" "ucontext_t *uc" "const void *hint" .Sh DESCRIPTION .Fn _lwp_park can be used to synchronise access to resources among multiple light-weight processes. It causes the calling LWP to wait interruptably in the kernel, until one of the following conditions is met: l -bullet t The .Fa abstime argument is non-NULL, and the absolute UTC time it specifies has has passed. t The LWP receives a directed signal posted using .Fn _lwp_kill , or is elected to handle a signal on behalf of its containing process. t The LWP is awoken by another LWP in the same process that has made a call to .Fn _lwp_wakeup . t The LWP is awoken by another LWP in the same process that has made a call to .Fn _lwp_unpark or .Fn _lwp_unpark_all . .El
p The preferred method to awaken an LWP sleeping as a result of a call to .Fn _lwp_park is to make a call to .Fn _lwp_unpark , or .Fn _lwp_unpark_all . The .Fn _lwp_wakeup system call is a more general facility, and requires more resources to execute.
p The .Fa uc argument is reserved, and for the current version of the system must be specified as .Dv NULL . The optional .Fa hint argument specifies the address of object upon which the LWP is synchronizing. When the .Fa hint value is matched between calls to .Fn _lwp_park and .Fn _lwp_unpark or .Fn _lwp_unpark_all , it may reduce the time necessary for the system to resume execution of waiting LWPs. .Sh RETURN VALUES .Fn _lwp_park may return a value of 0. Otherwise, -1 is returned and .Va errno is set to provide more information. .Sh ERRORS l -tag -width [EINVAL] t Bq Er ETIMEDOUT The UTC time specified by .Fa abstime has passed. t Bq Er EINVAL The time value specified by .Fa abstime is invalid. t Bq Er EINTR The LWP has been awoken by a signal or by a call to one of the following functions: .Fn _lwp_unpark , .Fn _lwp_unpark_all , .Fn _lwp_wakeup . t Bq Er EALREADY A request was made to wake the LWP before it began to wait in the kernel. .El .Sh SEE ALSO .Xr _lwp_unpark 2 , .Xr _lwp_unpark_all 2 , .Xr _lwp_wakeup 2 .Sh HISTORY The .Fn _lwp_park system call first appeared in .Nx 5.0 .