NAME
rump_lwproc —
rump kernel process/lwp
management
LIBRARY
rump kernel (librump, -lrump)
SYNOPSIS
#include <rump/rump.h>
int
rump_pub_lwproc_rfork(
int
flags);
int
rump_pub_lwproc_newlwp(
pid_t
pid);
void
rump_pub_lwproc_switch(
struct
lwp *l);
void
rump_pub_lwproc_releaselwp();
struct lwp *
rump_pub_lwproc_curlwp();
DESCRIPTION
In a normal operating system model a process is a resource container and a
thread (lwp) is the execution context. Every lwp is associated with exactly
one process, and a process is associated with one or more lwps. The current
lwp (curlwp) indicates the current process and determines which resources,
such as UID/GID, current working directory, and file descriptor table, are
currently used. These basic principles apply to rump kernels as well, but
since a rump kernel uses the host's thread and process context directly, the
rules for how thread context is determined are different.
In the rump kernel model, each host thread (implemented for example with
pthreads or green threads) is either bound to a rump kernel lwp or accesses
the rump kernel with an implicit thread context associated with pid 1. An
implicit thread context is created every time the rump kernel is entered and
disbanded upon exit. While convenient for occasional calls, creating an
implicit thread uses a shared resource which can become highly contended in a
multithreaded situation. It is therefore recommended that dedicated threads
are created.
The association between host threads and the rump kernel curlwp is left to the
caller. It is possible to create a dedicated host thread for every rump kernel
lwp or multiplex them on top of a single host thread. After rump kernel lwps
have been created, switching curlwp is very cheap. In case multiple
lwps/processes are created, it is the caller's responsibility to keep track of
them and release them when they are no longer necessary. A rump kernel lwp
will persist until it is explicitly released. A rump kernel process will
persist until all of its lwps have been released, at which point the process
is automatically released.
-
-
- rump_pub_lwproc_rfork()
- Create a process, one lwp inside it and set curlwp to the
new lwp. The flags parameter controls how file
descriptors are inherited from the parent. By default (flags=0) file
descriptors are shared. Other options are:
-
-
RUMP_RFFDG
- Copy file descriptors from parent. This is what
fork(2) does.
-
-
RUMP_RFCFDG
- File descriptors neither copied nor shared, i.e. new
process does not have access to the parent's file descriptors.
This routine returns 0 for success or an errno indicating the reason for
failure. The new process id can be retrieved in the normal fashion by
calling rump_sys_getpid().
-
-
- rump_pub_lwproc_newlwp(pid)
- Create a new lwp attached to the process specified by
pid. Sets curlwp to the new lwp. This routine
returns 0 for success or an errno indicating the reason for failure.
-
-
- rump_pub_lwproc_switch(l)
- Sets curlwp to l. In case the new
thread is associated with a different process than the current one, the
process context is also switched. The special value
NULL
sets curlwp to implicit context. Switching to
an already running lwp, i.e. attempting to use the same curlwp in two host
threads simultaneously causes a fatal error.
-
-
- rump_pub_lwproc_releaselwp()
- Release curlwp and set curlwp to implicit context. In case
curlwp was the last thread inside the current process, the process
container is also released. Calling this routine without a dedicated
curlwp is a fatal error.
-
-
- rump_pub_lwproc_curlwp()
- Returns curlwp or
NULL
if the
current context is an implicit context.
RETURN VALUES
rump_pub_lwproc_rfork() and
rump_pub_lwproc_newlwp() return 0 on success or an errno
indicating the reason for failure.
rump_pub_lwproc_curlwp()
returns curlwp or
NULL
if the current context is an
implicit context.
SEE ALSO
getpid(2),
rump(3)
HISTORY
rump_lwproc first appeared in
NetBSD
6.0.