Modify or examine the signal-blocked mask of a thread
#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 );
As a special case, you can use the how argument to query the current set of pending signals:
You can use various combinations of set and oldset to query or change (or both) the signal-blocked mask for a signal.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
These kernel calls modify or examine 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.
The SignalProcmask() and SignalProcmask_r() functions are identical, except in the way they indicate errors. See the Returns section for details.
When a signal is unmasked, the kernel checks for pending signals on the thread and, if there aren't any pending, checks for pending signals on the process:
|Signal pending on thread||The signal is immediately acted upon.|
|Signal pending on process||The signal is moved to the thread and is immediately acted upon.|
|No signal pending||No signal action performed until delivery of an unblocked signal.|
It isn't possible to block the SIGCONT, SIGKILL, or SIGSTOP signals. It also isn't possible to unmask the special Neutrino signals (SIGSELECT, SIGPHOTON, and six unnamed ones).
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 can:
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.
These calls don't block.
The only difference between these functions is the way they indicate errors:
pthread_sigmask(), SignalAction(), SignalKill(), sigprocmask()