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IvorySQL/src/fe_utils/cancel.c at master · IvorySQL/IvorySQL · GitHub
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fe_utils
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cancel.c
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fe_utils
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cancel.c
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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) 1996-2026, 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
)
{
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
);
}
}
}
/*
* setup_cancel_handler
*
* Register query cancellation callback for SIGINT.
*/
void
setup_cancel_handler
(
void
(
*
query_cancel_callback
) (
void
))
{
cancel_callback
=
query_cancel_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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