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.Dd May 11, 2016 .Dt LGRAB 3PROC .Os .Sh NAME .Nm Lgrab .Nd obtain a handle to control a thread .Sh SYNOPSIS .Lb libproc n libproc.h .Ft "struct ps_lwphandle *" .Fo Lgrab .Fa "struct ps_prochandle *P" .Fa "lwpid_t lwpid" .Fa "int *perr" .Fc .Sh DESCRIPTION The .Fn Lgrab function obtains a control handle to the thread identified by .Fa lwpid residing under the process .Fa P . This handle is then passed as argument to other .Sy libproc routines. The .Fa lwpid can be obtained from the .Sy pr_lwpid member of the .Sy lwpstatus_t structure.

p The .Fa perr argument must point to a valid pointer that will be used to store an error code in the event that .Fn Lgrab is unable to successfully obtain a handle to the process. The possible errors are defined below in the .Sx ERRORS section. The code may be transformed into a human readable string through the use of .Xr Lgrab_error 3PROC .

p The handle to the thread is valid until the .Xr Lfree 3PROC function is called, which also releases associated resources from the handle. Only a single handle to a specific thread may exist at any time. If the handle already exists and another caller attempts to grab that thread, it will result in an error. The caller must call .Fn Lfree before releasing the handle associated with .Fa P .

p Unlike grabbing a process, grabbing a thread does not change the current state of the thread. If it is running, it will remain running. If it is stopped, it will remain stopped. .Sh RETURN VALUES Upon successful completion, the .Fn Lgrab function returns a pointer to the control handle for the specified thread. Otherwise, the .Dv NULL pointer is returned and .Fa perr is set to indicate the error. .Sh ERRORS The .Fn Lgrab function will fail if: l -tag -width Er t Er G_BUSY Another handle already exists for the thread identified by .Fa lwpid . The handle need not exist in the current process and may exist in another process. t Er G_NOPROC The thread identified by .Fa lwpid does not exist or has already become a zombie. t Er G_STRANGE An unanticipated system error occurred while trying to create the handle. When this occurs, then the value of .Sy errno is meaningful. See .Xr errno 3C for more information and .Xr Intro 2 for the list of possible errors. .El .Sh INTERFACE STABILITY .Sy Uncommitted .Sh MT-LEVEL .Sy MT-Safe .Sh SEE ALSO .Xr errno 3C , .Xr libproc 3LIB , .Xr Lfree 3PROC , .Xr Lgrab_error 3PROC , .Xr proc 4