postgresql/src/backend/libpq/pqsignal.c

/*-------------------------------------------------------------------------
 *
 * pqsignal.c
 *	  reliable BSD-style signal(2) routine stolen from RWW who stole it
 *	  from Stevens...
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/libpq/pqsignal.c,v 1.32 2004/02/18 16:25:12 momjian Exp $
 *
 * NOTES
 *		This shouldn't be in libpq, but the monitor and some other
 *		things need it...
 *
 *	A NOTE ABOUT SIGNAL HANDLING ACROSS THE VARIOUS PLATFORMS.
 *
 *	pg_config.h defines the macro HAVE_POSIX_SIGNALS for some platforms and
 *	not for others.  This file and pqsignal.h use that macro to decide
 *	how to handle signalling.
 *
 *	signal(2) handling - this is here because it affects some of
 *	the frontend commands as well as the backend server.
 *
 *	Ultrix and SunOS provide BSD signal(2) semantics by default.
 *
 *	SVID2 and POSIX signal(2) semantics differ from BSD signal(2)
 *	semantics.	We can use the POSIX sigaction(2) on systems that
 *	allow us to request restartable signals (SA_RESTART).
 *
 *	Some systems don't allow restartable signals at all unless we
 *	link to a special BSD library.
 *
 *	We devoutly hope that there aren't any systems that provide
 *	neither POSIX signals nor BSD signals.	The alternative
 *	is to do signal-handler reinstallation, which doesn't work well
 *	at all.
 * ------------------------------------------------------------------------*/
#ifdef WIN32
#define _WIN32_WINNT 0x0400
#endif

#include "postgres.h"

#include <signal.h>

#include "libpq/pqsignal.h"


/*
 * Initialize BlockSig, UnBlockSig, and AuthBlockSig.
 *
 * BlockSig is the set of signals to block when we are trying to block
 * signals.  This includes all signals we normally expect to get, but NOT
 * signals that should never be turned off.
 *
 * AuthBlockSig is the set of signals to block during authentication;
 * it's essentially BlockSig minus SIGTERM, SIGQUIT, SIGALRM.
 *
 * UnBlockSig is the set of signals to block when we don't want to block
 * signals (is this ever nonzero??)
 */
void
pqinitmask(void)
{
#ifdef HAVE_SIGPROCMASK
	sigemptyset(&UnBlockSig);
	sigfillset(&BlockSig);
	sigfillset(&AuthBlockSig);

	/*
	 * Unmark those signals that should never be blocked. Some of these
	 * signal names don't exist on all platforms.  Most do, but might as
	 * well ifdef them all for consistency...
	 */
#ifdef SIGTRAP
	sigdelset(&BlockSig, SIGTRAP);
	sigdelset(&AuthBlockSig, SIGTRAP);
#endif
#ifdef SIGABRT
	sigdelset(&BlockSig, SIGABRT);
	sigdelset(&AuthBlockSig, SIGABRT);
#endif
#ifdef SIGILL
	sigdelset(&BlockSig, SIGILL);
	sigdelset(&AuthBlockSig, SIGILL);
#endif
#ifdef SIGFPE
	sigdelset(&BlockSig, SIGFPE);
	sigdelset(&AuthBlockSig, SIGFPE);
#endif
#ifdef SIGSEGV
	sigdelset(&BlockSig, SIGSEGV);
	sigdelset(&AuthBlockSig, SIGSEGV);
#endif
#ifdef SIGBUS
	sigdelset(&BlockSig, SIGBUS);
	sigdelset(&AuthBlockSig, SIGBUS);
#endif
#ifdef SIGSYS
	sigdelset(&BlockSig, SIGSYS);
	sigdelset(&AuthBlockSig, SIGSYS);
#endif
#ifdef SIGCONT
	sigdelset(&BlockSig, SIGCONT);
	sigdelset(&AuthBlockSig, SIGCONT);
#endif
#ifdef SIGTERM
	sigdelset(&AuthBlockSig, SIGTERM);
#endif
#ifdef SIGQUIT
	sigdelset(&AuthBlockSig, SIGQUIT);
#endif
#ifdef SIGALRM
	sigdelset(&AuthBlockSig, SIGALRM);
#endif
#else
	UnBlockSig = 0;
	BlockSig = sigmask(SIGHUP) | sigmask(SIGQUIT) |
		sigmask(SIGTERM) | sigmask(SIGALRM) |
		sigmask(SIGINT) | sigmask(SIGUSR1) |
		sigmask(SIGUSR2) | sigmask(SIGCHLD) |
		sigmask(SIGWINCH) | sigmask(SIGFPE);
	AuthBlockSig = sigmask(SIGHUP) |
		sigmask(SIGINT) | sigmask(SIGUSR1) |
		sigmask(SIGUSR2) | sigmask(SIGCHLD) |
		sigmask(SIGWINCH) | sigmask(SIGFPE);
#endif
}


#ifndef WIN32
/*
 * Set up a signal handler
 */
pqsigfunc
pqsignal(int signo, pqsigfunc func)
{
#if !defined(HAVE_POSIX_SIGNALS)
	return signal(signo, func);
#else
	struct sigaction act,
				oact;

	act.sa_handler = func;
	sigemptyset(&act.sa_mask);
	act.sa_flags = 0;
	if (signo != SIGALRM)
		act.sa_flags |= SA_RESTART;
	if (sigaction(signo, &act, &oact) < 0)
		return SIG_ERR;
	return oact.sa_handler;
#endif   /* !HAVE_POSIX_SIGNALS */
}


#else


/* Win32 specific signals code */

/* pg_signal_crit_sec is used to protect only pg_signal_queue. That is the only
 * variable that can be accessed from the signal sending threads! */
static CRITICAL_SECTION pg_signal_crit_sec;
static int	pg_signal_queue;

#define PG_SIGNAL_COUNT 32
static pqsigfunc pg_signal_array[PG_SIGNAL_COUNT];
static pqsigfunc pg_signal_defaults[PG_SIGNAL_COUNT];
static int	pg_signal_mask;

HANDLE		pgwin32_main_thread_handle;

/* Signal handling thread function */
static DWORD WINAPI pg_signal_thread(LPVOID param);
static BOOL WINAPI pg_console_handler(DWORD dwCtrlType);

/* Initialization */
void
pgwin32_signal_initialize(void)
{
	int			i;
	HANDLE		signal_thread_handle;

	InitializeCriticalSection(&pg_signal_crit_sec);

	for (i = 0; i < PG_SIGNAL_COUNT; i++)
	{
		pg_signal_array[i] = SIG_DFL;
		pg_signal_defaults[i] = SIG_IGN;
	}
	pg_signal_mask = 0;
	pg_signal_queue = 0;

	/* Get handle to main thread so we can post calls to it later */
	if (!DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
						 GetCurrentProcess(), &pgwin32_main_thread_handle,
						 0, FALSE, DUPLICATE_SAME_ACCESS))
		ereport(FATAL,
				(errmsg_internal("Failed to get main thread handle!")));
	
	/* Create thread for handling signals */
	signal_thread_handle = CreateThread(NULL, 0, pg_signal_thread, NULL, 0, NULL);
	if (signal_thread_handle == NULL)
		ereport(FATAL,
				(errmsg_internal("Failed to create signal handler thread!")));

	if (!SetConsoleCtrlHandler(pg_console_handler, TRUE)) 
		ereport(FATAL,
				(errmsg_internal("Failed to set console control handler!")));
}


/* Dispatch all signals currently queued and not blocked
 * Blocked signals are ignored, and will be fired at the time of
 * the sigsetmask() call. */
static void
dispatch_queued_signals(void)
{
	int			i;

	EnterCriticalSection(&pg_signal_crit_sec);
	while (pg_signal_queue & ~pg_signal_mask)
	{
		/* One or more unblocked signals queued for execution */

		int			exec_mask = pg_signal_queue & ~pg_signal_mask;

		for (i = 0; i < PG_SIGNAL_COUNT; i++)
		{
			if (exec_mask & sigmask(i))
			{
				/* Execute this signal */
				pqsigfunc	sig = pg_signal_array[i];

				if (sig == SIG_DFL)
					sig = pg_signal_defaults[i];
				pg_signal_queue &= ~sigmask(i);
				if (sig != SIG_ERR && sig != SIG_IGN && sig != SIG_DFL)
				{
					LeaveCriticalSection(&pg_signal_crit_sec);
					sig(i);
					EnterCriticalSection(&pg_signal_crit_sec);
					break;		/* Restart outer loop, in case signal mask
								 * or queue has been modified inside
								 * signal handler */
				}
			}
		}
	}
	LeaveCriticalSection(&pg_signal_crit_sec);
}

/* signal masking. Only called on main thread, no sync required */
int
pqsigsetmask(int mask)
{
	int			prevmask;

	prevmask = pg_signal_mask;
	pg_signal_mask = mask;

	/*
	 * Dispatch any signals queued up right away, in case we have
	 * unblocked one or more signals previously queued
	 */
	dispatch_queued_signals();

	return prevmask;
}


/* signal manipulation. Only called on main thread, no sync required */
pqsigfunc
pqsignal(int signum, pqsigfunc handler)
{
	pqsigfunc	prevfunc;

	if (signum >= PG_SIGNAL_COUNT || signum < 0)
		return SIG_ERR;
	prevfunc = pg_signal_array[signum];
	pg_signal_array[signum] = handler;
	return prevfunc;
}

/* signal sending */
int
pqkill(int pid, int sig)
{
	char		pipename[128];
	BYTE		sigData = sig;
	BYTE		sigRet = 0;
	DWORD		bytes;

	if (sig >= PG_SIGNAL_COUNT || sig <= 0)
	{
		errno = EINVAL;
		return -1;
	}
	if (pid <= 0)
	{
		/* No support for process groups */
		errno = EINVAL;
		return -1;
	}
	wsprintf(pipename, "\\\\.\\pipe\\pgsignal_%i", pid);
	if (!CallNamedPipe(pipename, &sigData, 1, &sigRet, 1, &bytes, 1000))
	{
		if (GetLastError() == ERROR_FILE_NOT_FOUND)
			errno = ESRCH;
		else if (GetLastError() == ERROR_ACCESS_DENIED)
			errno = EPERM;
		else
			errno = EINVAL;
		return -1;
	}
	if (bytes != 1 || sigRet != sig)
	{
		errno = ESRCH;
		return -1;
	}

	return 0;
}

/* APC callback scheduled on main thread when signals are fired */
static void CALLBACK
pg_signal_apc(ULONG_PTR param)
{
	dispatch_queued_signals();
}

/*
 * All functions below execute on the signal handler thread
 * and must be synchronized as such!
 * NOTE! The only global variable that can be used is
 * pg_signal_queue!
 */


void
pg_queue_signal(int signum)
{
	if (signum >= PG_SIGNAL_COUNT || signum < 0)
		return;

	EnterCriticalSection(&pg_signal_crit_sec);
	pg_signal_queue |= sigmask(signum);
	LeaveCriticalSection(&pg_signal_crit_sec);

	QueueUserAPC(pg_signal_apc, pgwin32_main_thread_handle, (ULONG_PTR) NULL);
}

/* Signal dispatching thread */
static DWORD WINAPI
pg_signal_dispatch_thread(LPVOID param)
{
	HANDLE		pipe = (HANDLE) param;
	BYTE		sigNum;
	DWORD		bytes;

	if (!ReadFile(pipe, &sigNum, 1, &bytes, NULL))
	{
		/* Client died before sending */
		CloseHandle(pipe);
		return 0;
	}
	if (bytes != 1)
	{
		/* Received <bytes> bytes over signal pipe (should be 1) */
		CloseHandle(pipe);
		return 0;
	}
	WriteFile(pipe, &sigNum, 1, &bytes, NULL);	/* Don't care if it works
												 * or not.. */
	FlushFileBuffers(pipe);
	DisconnectNamedPipe(pipe);
	CloseHandle(pipe);

	pg_queue_signal(sigNum);
	return 0;
}

/* Signal handling thread */
static DWORD WINAPI
pg_signal_thread(LPVOID param)
{
	char		pipename[128];
	HANDLE		pipe = INVALID_HANDLE_VALUE;

	wsprintf(pipename, "\\\\.\\pipe\\pgsignal_%i", GetCurrentProcessId());

	for (;;)
	{
		BOOL		fConnected;
		HANDLE		hThread;

		pipe = CreateNamedPipe(pipename, PIPE_ACCESS_DUPLEX,
				   PIPE_TYPE_MESSAGE | PIPE_READMODE_MESSAGE | PIPE_WAIT,
						   PIPE_UNLIMITED_INSTANCES, 16, 16, 1000, NULL);
		if (pipe == INVALID_HANDLE_VALUE)
		{
			fprintf(stderr, gettext("Failed to create signal listener pipe: %i. Retrying.\n"), (int) GetLastError());
			SleepEx(500, TRUE);
			continue;
		}

		fConnected = ConnectNamedPipe(pipe, NULL) ? TRUE : (GetLastError() == ERROR_PIPE_CONNECTED);
		if (fConnected)
		{
			hThread = CreateThread(NULL, 0,
					  (LPTHREAD_START_ROUTINE) pg_signal_dispatch_thread,
								   (LPVOID) pipe, 0, NULL);
			if (hThread == INVALID_HANDLE_VALUE)
				fprintf(stderr, gettext("Failed to create signal dispatch thread: %i\n"), (int) GetLastError());
			else
				CloseHandle(hThread);
		}
		else
			/* Connection failed. Cleanup and try again */
			CloseHandle(pipe);
	}
	return 0;
}


/* Console control handler will execute on a thread created 
   by the OS at the time of invocation */
static BOOL WINAPI pg_console_handler(DWORD dwCtrlType) {
	if (dwCtrlType == CTRL_C_EVENT ||
		dwCtrlType == CTRL_BREAK_EVENT ||
		dwCtrlType == CTRL_CLOSE_EVENT ||
		dwCtrlType == CTRL_SHUTDOWN_EVENT) {
		pg_queue_signal(SIGINT);
		return TRUE;
	}
	return FALSE;
}


#endif