SignalProcmask(), SignalProcmask_r()

Modify or examine the signal blocked mask of a thread

Synopsis:

#include <sys/neutrino.h>

int SignalProcmask( pid_t pid,
                    int tid,
                    int how,
                    const sigset_t* set,
                    sigset_t* oldset );

int SignalProcmask_r( pid_t pid,
                      int tid,
                      int how,
                      const sigset_t* set,
                      sigset_t* oldset );

Library:

libc

Description:

The SignalProcmask() and SignalProcmask_r() functions are identical except in the way they indicate errors. See the Returns section for details.

These kernel calls modify or examines the signal blocked mask of the thread tid in process pid. If pid is zero, the current process is assumed. If tid is zero, pid is ignored and the calling thread is used.

If the value of set isn't NULL, it points to a set of signals to be used to change the currently blocked set. The value of how indicates the manner in which the set is changed:

SIG_BLOCK

The resulting set is the union of the current set and the signal set pointed to by set.

SIG_UNBLOCK

The resulting set is the intersection of the current set and the signal set pointed to by set.

SIG_SETMASK

The resulting set is the signal set pointed to by set.

As a special case, the how argument can be used to query the current set of pending signals:

SIG_PENDING

The combined set of pending signals on the thread and process are saved in the signal set pointed to by oldset. The set argument is ignored.

If the value of oldset isn't NULL, the previous blocked mask is saved there. The combination of set and oldset allows you to query or change (or both) the signal blocked mask for a signal.

When a signal is unmasked, the kernel checks for pending signals on the thread and, if there are none pending, on the process:

It isn't possible to block the SIGKILL or SIGSTOP signals.

When a signal handler is invoked, the signal responsible is automatically masked before its handler is called (see SignalAction()). If the handler returns normally, the operating system restores the signal mask present just before the handler was called as an atomic operation. Changes made using SignalProcmask() in the handler are undone.

When a signal is targeted at a process, the kernel delivers it to at most one thread (see SignalKill()) that has the signal unblocked. If multiple threads have the signal unblocked, only one thread is given the signal. Which thread receives the signal isn't deterministic. To make it deterministic, you have two choices:

• Have all threads except one block all signals; that thread handles all signals.
• Target signals to specific threads.

If all threads have the signal blocked, it's made pending on the process. The first thread to unblock the signal receives the pending signal. If a signal is pending on a thread, it's never retargetted to the process or another thread, regardless of changes to the signal-blocked mask.

Signals targeted at a thread always affect that thread alone.

Blocking states

These calls don't block.

Returns:

The only difference between these functions is the way they indicate errors:

SignalProcmask()

If an error occurs, -1 is returned and errno is set. Any other value returned indicates success.

SignalProcmask_r()

EOK is returned on success. This function does NOT set errno. If an error occurs, any value in the Errors section may be returned.

Errors:

EAGAIN

The system's unable to allocate a signal handler. This indicates critically low memory.

EFAULT

A fault occurred when the kernel tried to access the buffers provided.

EINVAL

The value of how is invalid. Attempt to set SIGKILL or SIGSTOP to something other than SIG_DFL.

EPERM

The process doesn't have permission to change the signal mask of the specified process.

ESRCH

The process indicated by pid or thread indicated by tid doesn't exist.

Classification:

QNX 6

See also:

SignalAction(), SignalKill()