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