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/*------------------------------------------------------------------------
*
* Query cancellation support for frontend code
*
* Assorted utility functions to control query cancellation with signal
* handler for SIGINT.
*
*
* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/fe-utils/cancel.c
*
*------------------------------------------------------------------------
*/
#include "postgres_fe.h"
#include <unistd.h>
#include "common/connect.h"
#include "fe_utils/cancel.h"
#include "fe_utils/string_utils.h"
/*
* Write a simple string to stderr --- must be safe in a signal handler.
* We ignore the write() result since there's not much we could do about it.
* Certain compilers make that harder than it ought to be.
*/
#define write_stderr(str) \
do { \
const char *str_ = (str); \
int rc_; \
rc_ = write(fileno(stderr), str_, strlen(str_)); \
(void) rc_; \
} while (0)
/*
* Contains all the information needed to cancel a query issued from
* a database connection to the backend.
*/
static PGcancel *volatile cancelConn = NULL;
/*
* Predetermined localized error strings --- needed to avoid trying
* to call gettext() from a signal handler.
*/
static const char *cancel_sent_msg = NULL;
static const char *cancel_not_sent_msg = NULL;
/*
* CancelRequested is set when we receive SIGINT (or local equivalent).
* There is no provision in this module for resetting it; but applications
* might choose to clear it after successfully recovering from a cancel.
* Note that there is no guarantee that we successfully sent a Cancel request,
* or that the request will have any effect if we did send it.
*/
volatile sig_atomic_t CancelRequested = false;
#ifdef WIN32
static CRITICAL_SECTION cancelConnLock;
#endif
/*
* Additional callback for cancellations.
*/
static void (*cancel_callback) (void) = NULL;
/*
* SetCancelConn
*
* Set cancelConn to point to the current database connection.
*/
void
SetCancelConn(PGconn *conn)
{
PGcancel *oldCancelConn;
#ifdef WIN32
EnterCriticalSection(&cancelConnLock);
#endif
/* Free the old one if we have one */
oldCancelConn = cancelConn;
/* be sure handle_sigint doesn't use pointer while freeing */
cancelConn = NULL;
if (oldCancelConn != NULL)
PQfreeCancel(oldCancelConn);
cancelConn = PQgetCancel(conn);
#ifdef WIN32
LeaveCriticalSection(&cancelConnLock);
#endif
}
/*
* ResetCancelConn
*
* Free the current cancel connection, if any, and set to NULL.
*/
void
ResetCancelConn(void)
{
PGcancel *oldCancelConn;
#ifdef WIN32
EnterCriticalSection(&cancelConnLock);
#endif
oldCancelConn = cancelConn;
/* be sure handle_sigint doesn't use pointer while freeing */
cancelConn = NULL;
if (oldCancelConn != NULL)
PQfreeCancel(oldCancelConn);
#ifdef WIN32
LeaveCriticalSection(&cancelConnLock);
#endif
}
/*
* Code to support query cancellation
*
* Note that sending the cancel directly from the signal handler is safe
* because PQcancel() is written to make it so. We use write() to report
* to stderr because it's better to use simple facilities in a signal
* handler.
*
* On Windows, the signal canceling happens on a separate thread, because
* that's how SetConsoleCtrlHandler works. The PQcancel function is safe
* for this (unlike PQrequestCancel). However, a CRITICAL_SECTION is required
* to protect the PGcancel structure against being changed while the signal
* thread is using it.
*/
#ifndef WIN32
/*
* handle_sigint
*
* Handle interrupt signals by canceling the current command, if cancelConn
* is set.
*/
static void
handle_sigint(SIGNAL_ARGS)
{
int save_errno = errno;
char errbuf[256];
CancelRequested = true;
if (cancel_callback != NULL)
cancel_callback();
/* Send QueryCancel if we are processing a database query */
if (cancelConn != NULL)
{
if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
{
write_stderr(cancel_sent_msg);
}
else
{
write_stderr(cancel_not_sent_msg);
write_stderr(errbuf);
}
}
errno = save_errno; /* just in case the write changed it */
}
/*
* setup_cancel_handler
*
* Register query cancellation callback for SIGINT.
*/
void
setup_cancel_handler(void (*callback) (void))
{
cancel_callback = callback;
cancel_sent_msg = _("Cancel request sent\n");
cancel_not_sent_msg = _("Could not send cancel request: ");
pqsignal(SIGINT, handle_sigint);
}
#else /* WIN32 */
static BOOL WINAPI
consoleHandler(DWORD dwCtrlType)
{
char errbuf[256];
if (dwCtrlType == CTRL_C_EVENT ||
dwCtrlType == CTRL_BREAK_EVENT)
{
CancelRequested = true;
if (cancel_callback != NULL)
cancel_callback();
/* Send QueryCancel if we are processing a database query */
EnterCriticalSection(&cancelConnLock);
if (cancelConn != NULL)
{
if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
{
write_stderr(cancel_sent_msg);
}
else
{
write_stderr(cancel_not_sent_msg);
write_stderr(errbuf);
}
}
LeaveCriticalSection(&cancelConnLock);
return TRUE;
}
else
/* Return FALSE for any signals not being handled */
return FALSE;
}
void
setup_cancel_handler(void (*callback) (void))
{
cancel_callback = callback;
cancel_sent_msg = _("Cancel request sent\n");
cancel_not_sent_msg = _("Could not send cancel request: ");
InitializeCriticalSection(&cancelConnLock);
SetConsoleCtrlHandler(consoleHandler, TRUE);
}
#endif /* WIN32 */
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