[libs] Fix poll events conversion

[trungnt2910]

• Use bitwise and to check for all flags instead of using a switch statement for poll events flags conversion.
• Convert poll events before comparison in assert statement.

[stephentoub]

Why?

[trungnt2910]

The problem does not appear on Linux or other UNIXes as they use the same values as the PollEvents enum in the PAL.

However, there don't seem to be any standard mandating the underlying values of these flags, and on Haiku these flags have different values.

Because there are no standards for the values, I don't think it is correct to assume the values are the same for the PAL and the underlying platform.

As this change affects cross-platform code I decided to open a PR separate from my Haiku-specific changes.

[stephentoub]

I'm not understanding. The whole purpose of these methods is to map between the PAL values and the OS values which may not match. You're saying your new version works and the existing ones fail?

[trungnt2910]

Unless there is something I am missing, the existing code has two issues:

• It uses switch to map a set of flags between PAL and OS values:

runtime/src/native/libs/Common/pal_io_common.h

Lines 107 to 132 in 5b8437d

	switch (event->Events)
	{
	case PAL_POLLIN:
	pollfds[i].events = POLLIN;
	break;
	#ifdef POLLPRI // not available in WASI
	case PAL_POLLPRI:
	pollfds[i].events = POLLPRI;
	break;
	#endif
	case PAL_POLLOUT:
	pollfds[i].events = POLLOUT;
	break;
	case PAL_POLLERR:
	pollfds[i].events = POLLERR;
	break;
	case PAL_POLLHUP:
	pollfds[i].events = POLLHUP;
	break;
	case PAL_POLLNVAL:
	pollfds[i].events = POLLNVAL;
	break;
	default:
	pollfds[i].events = event->Events;
	break;
	}

When a set containing two or more flags is passed (for example, PAL_POLLIN | PAL_POLLOUT), the existing code falls to the default label which does no mapping at all.

The same applies to the reverse mapping:

runtime/src/native/libs/Common/pal_io_common.h

Lines 157 to 182 in 5b8437d

	switch (pfd->revents)
	{
	case POLLIN:
	pollEvents[i].TriggeredEvents = PAL_POLLIN;
	break;
	#ifdef POLLPRI // not available in WASI
	case POLLPRI:
	pollEvents[i].TriggeredEvents = PAL_POLLPRI;
	break;
	#endif
	case POLLOUT:
	pollEvents[i].TriggeredEvents = PAL_POLLOUT;
	break;
	case POLLERR:
	pollEvents[i].TriggeredEvents = PAL_POLLERR;
	break;
	case POLLHUP:
	pollEvents[i].TriggeredEvents = PAL_POLLHUP;
	break;
	case POLLNVAL:
	pollEvents[i].TriggeredEvents = PAL_POLLNVAL;
	break;
	default:
	pollEvents[i].TriggeredEvents = (int16_t)pfd->revents;
	break;
	}

• It uses a runtime assert to check that the integer representation of the converted flags is equal to that of the PAL flags:

runtime/src/native/libs/Common/pal_io_common.h

Line 154 in 5b8437d

assert(pfd->events == pollEvents[i].Events);

The assert seems to have meant to ensure that the poll syscall did not modify fields it is not supposed to touch.

Neither of these issues are visible on Linux and some other UNIXes since the PAL flags and the OS flags are the same (probably the flags were chosen to match Linux and other platforms all coincidentally have the same flags?). The default block on these platforms still produce seemingly correct results and the assert still passes since no conversion is actually done.

On Haiku, or any other platforms with a different representation of the poll flags, the problems become apparent. For these platforms, it is true that my version works and the existing ones fail.

[ghost]

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Issue Details

---

• Use bitwise and to check for all flags instead of using a switch statement for poll events flags conversion.
• Convert poll events before comparison in assert statement.

Author:	trungnt2910
Assignees:	-
Labels:	area-System.IO, area-PAL-coreclr, community-contribution
Milestone:	-

[ghost]

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See info in area-owners.md if you want to be subscribed.

Issue Details

---

• Use bitwise and to check for all flags instead of using a switch statement for poll events flags conversion.
• Convert poll events before comparison in assert statement.

Author:	trungnt2910
Assignees:	-
Labels:	area-System.IO, area-System.Net.Sockets, community-contribution
Milestone:	-

[wfurt]

LGTM