BadVPN – Rev 1
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/**
* @file dead.h
* @author Ambroz Bizjak <ambrop7@gmail.com>
*
* @section LICENSE
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the author nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* @section DESCRIPTION
*
* Dead mechanism definitions.
*
* The dead mechanism is a way for a piece of code to detect whether some
* specific event has occured during some operation (usually during calling
* a user-provided handler function), without requiring access to memory
* that might no longer be available because of the event.
*
* It works somehow like that:
*
* First a dead variable ({@link dead_t}) is allocated somewhere, and
* initialized with {@link DEAD_INIT}, e.g.:
* DEAD_INIT(dead);
*
* When the event that needs to be caught occurs, {@link DEAD_KILL} is
* called, e.g.:
* DEAD_KILL(dead);
* The memory used by the dead variable is no longer needed after
* that.
*
* If a piece of code needs to know whether the event occured during some
* operation (but it must not have occured before!), it puts {@link DEAD_ENTER}}
* in front of the operation, and does {@link DEAD_LEAVE} at the end. If
* {@link DEAD_LEAVE} returned nonzero, the event occured, otherwise it did
* not. Example:
* DEAD_ENTER(dead)
* HandlerFunction();
* if (DEAD_LEAVE(dead)) {
* (event occured)
* }
*
* If is is needed to check for the event more than once in a single block,
* {@link DEAD_DECLARE} should be put somewhere before, and {@link DEAD_ENTER2}
* should be used instead of {@link DEAD_ENTER}.
*
* If it is needed to check for multiple events (dead variables) at the same
* time, DEAD_*_N macros should be used instead, specifying different
* identiers as the first argument for different dead variables.
*/
#ifndef BADVPN_MISC_DEAD_H
#define BADVPN_MISC_DEAD_H
#include <stdlib.h>
/**
* Dead variable.
*/
typedef int *dead_t;
/**
* Initializes a dead variable.
*/
#define DEAD_INIT(ptr) { ptr = NULL; }
/**
* Kills the dead variable,
*/
#define DEAD_KILL(ptr) { if (ptr) *(ptr) = 1; }
/**
* Kills the dead variable with the given value, or does nothing
* if the value is 0. The value will seen by {@link DEAD_KILLED}.
*/
#define DEAD_KILL_WITH(ptr, val) { if (ptr) *(ptr) = (val); }
/**
* Declares dead catching variables.
*/
#define DEAD_DECLARE int badvpn__dead; dead_t badvpn__prev_ptr;
/**
* Enters a dead catching using already declared dead catching variables.
* The dead variable must have been initialized with {@link DEAD_INIT},
* and {@link DEAD_KILL} must not have been called yet.
* {@link DEAD_LEAVE2} must be called before the current scope is left.
*/
#define DEAD_ENTER2(ptr) { badvpn__dead = 0; badvpn__prev_ptr = ptr; ptr = &badvpn__dead; }
/**
* Declares dead catching variables and enters a dead catching.
* The dead variable must have been initialized with {@link DEAD_INIT},
* and {@link DEAD_KILL} must not have been called yet.
* {@link DEAD_LEAVE2} must be called before the current scope is left.
*/
#define DEAD_ENTER(ptr) DEAD_DECLARE DEAD_ENTER2(ptr)
/**
* Leaves a dead catching.
*/
#define DEAD_LEAVE2(ptr) { if (!badvpn__dead) ptr = badvpn__prev_ptr; if (badvpn__prev_ptr) *badvpn__prev_ptr = badvpn__dead; }
/**
* Returns 1 if {@link DEAD_KILL} was called for the dead variable, 0 otherwise.
* Must be called after entering a dead catching.
*/
#define DEAD_KILLED (badvpn__dead)
#define DEAD_DECLARE_N(n) int badvpn__dead##n; dead_t badvpn__prev_ptr##n;
#define DEAD_ENTER2_N(n, ptr) { badvpn__dead##n = 0; badvpn__prev_ptr##n = ptr; ptr = &badvpn__dead##n;}
#define DEAD_ENTER_N(n, ptr) DEAD_DECLARE_N(n) DEAD_ENTER2_N(n, ptr)
#define DEAD_LEAVE2_N(n, ptr) { if (!badvpn__dead##n) ptr = badvpn__prev_ptr##n; if (badvpn__prev_ptr##n) *badvpn__prev_ptr##n = badvpn__dead##n; }
#define DEAD_KILLED_N(n) (badvpn__dead##n)
#endif