libutil: Provide alternatives to startSignalHandlerThread

How signals should be handled depends on what kind of process Nix
is integrated into. The signal handler thread used by the stand-alone
Nix commands / processes may not work well in the context of other
runtime systems, such as those of Python, Perl, or Haskell.
This commit is contained in:
Robert Hensing 2023-02-01 18:38:54 +01:00
parent 781d3dceb3
commit 2196fd1146
2 changed files with 61 additions and 2 deletions

View file

@ -1748,13 +1748,39 @@ void triggerInterrupt()
} }
static sigset_t savedSignalMask; static sigset_t savedSignalMask;
static bool savedSignalMaskIsSet = false;
void setChildSignalMask(sigset_t * sigs)
{
assert(sigs); // C style function, but think of sigs as a reference
#if _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
sigemptyset(&savedSignalMask);
// There's no "assign" or "copy" function, so we rely on (math) idempotence
// of the or operator: a or a = a.
sigorset(&savedSignalMask, sigs, sigs);
#else
// Without sigorset, our best bet is to assume that sigset_t is a type that
// can be assigned directly, such as is the case for a sigset_t defined as
// an integer type.
savedSignalMask = *sigs;
#endif
savedSignalMaskIsSet = true;
}
void saveSignalMask() {
if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask))
throw SysError("querying signal mask");
savedSignalMaskIsSet = true;
}
void startSignalHandlerThread() void startSignalHandlerThread()
{ {
updateWindowSize(); updateWindowSize();
if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask)) saveSignalMask();
throw SysError("querying signal mask");
sigset_t set; sigset_t set;
sigemptyset(&set); sigemptyset(&set);
@ -1771,6 +1797,20 @@ void startSignalHandlerThread()
static void restoreSignals() static void restoreSignals()
{ {
// If startSignalHandlerThread wasn't called, that means we're not running
// in a proper libmain process, but a process that presumably manages its
// own signal handlers. Such a process should call either
// - initNix(), to be a proper libmain process
// - startSignalHandlerThread(), to resemble libmain regarding signal
// handling only
// - saveSignalMask(), for processes that define their own signal handling
// thread
// TODO: Warn about this? Have a default signal mask? The latter depends on
// whether we should generally inherit signal masks from the caller.
// I don't know what the larger unix ecosystem expects from us here.
if (!savedSignalMaskIsSet)
return;
if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr)) if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
throw SysError("restoring signals"); throw SysError("restoring signals");
} }

View file

@ -448,6 +448,8 @@ void setStackSize(size_t stackSize);
/** /**
* Restore the original inherited Unix process context (such as signal * Restore the original inherited Unix process context (such as signal
* masks, stack size). * masks, stack size).
* See startSignalHandlerThread(), saveSignalMask().
*/ */
void restoreProcessContext(bool restoreMounts = true); void restoreProcessContext(bool restoreMounts = true);
@ -817,9 +819,26 @@ class Callback;
/** /**
* Start a thread that handles various signals. Also block those signals * Start a thread that handles various signals. Also block those signals
* on the current thread (and thus any threads created by it). * on the current thread (and thus any threads created by it).
* Saves the signal mask before changing the mask to block those signals.
* See saveSignalMask().
*/ */
void startSignalHandlerThread(); void startSignalHandlerThread();
/**
* Saves the signal mask, which is the signal mask that nix will restore
* before creating child processes.
* See setChildSignalMask() to set an arbitrary signal mask instead of the
* current mask.
*/
void saveSignalMask();
/**
* Sets the signal mask. Like saveSignalMask() but for a signal set that doesn't
* necessarily match the current thread's mask.
* See saveSignalMask() to set the saved mask to the current mask.
*/
void setChildSignalMask(sigset_t *sigs);
struct InterruptCallback struct InterruptCallback
{ {
virtual ~InterruptCallback() { }; virtual ~InterruptCallback() { };