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#ifdef RCSID
static char RCSid[] =
"$Header: d:/cvsroot/tads/tads3/VMUNDO.CPP,v 1.3 1999/07/11 00:46:58 MJRoberts Exp $";
#endif
/*
* Copyright (c) 1998, 2002 Michael J. Roberts. All Rights Reserved.
*
* Please see the accompanying license file, LICENSE.TXT, for information
* on using and copying this software.
*/
/*
Name
vmundo.cpp - undo manager
Function
Notes
Modified
10/29/98 MJRoberts - Creation
*/
#include "t3std.h"
#include "vmtype.h"
#include "vmobj.h"
#include "vmundo.h"
/*
* create the undo manager
*/
CVmUndo::CVmUndo(size_t undo_record_cnt, uint max_savepts)
{
/* remember the maximum number of savepoints */
max_savepts_ = (vm_savept_t)max_savepts;
/*
* initialize the savepoint to number 0 (this is arbitrary, but we
* might as well start here)
*/
cur_savept_ = 0;
/* no savepoints have been created yet */
savept_cnt_ = 0;
/* create the undo record array */
rec_arr_size_ = undo_record_cnt;
rec_arr_ = (CVmUndoMeta *)t3malloc(rec_arr_size_
* sizeof(rec_arr_[0]));
/* we have no records at all yet, so we have no "firsts" */
cur_first_ = 0;
oldest_first_ = 0;
/* start allocating from the first entry in the array */
next_free_ = rec_arr_;
}
/*
* delete the undo manager
*/
CVmUndo::~CVmUndo()
{
/* delete the array of undo records */
t3free(rec_arr_);
}
/*
* create a savepoint
*/
void CVmUndo::create_savept(VMG0_)
{
CVmUndoMeta *rec;
/*
* Allocate an undo record to serve as the link pointer for this
* savepoint. If this fails, we cannot create a savepoint; we won't
* need to do anything else in this case, since we will have deleted
* all existing savepoints if we ran out of records.
*/
rec = alloc_rec(vmg0_);
if (rec == 0)
return;
/* if we have an old savepoint, the new record starts the next one */
if (cur_first_ != 0)
cur_first_->link.next_first = rec;
/* the old savepoint (if any) is our previous savepoint */
rec->link.prev_first = cur_first_;
/* there's nothing after us yet */
rec->link.next_first = 0;
/* this record is now the current savepoint's first record */
cur_first_ = rec;
/*
* if we didn't have any savepoints recorded yet, this is now the
* first record in the oldest savepoint
*/
if (oldest_first_ == 0)
oldest_first_ = rec;
/*
* increment the savepoint number, wrapping to zero if we reach the
* highest value we can store
*/
if (cur_savept_ == VM_SAVEPT_MAX)
cur_savept_ = 0;
else
++cur_savept_;
/*
* if we're already storing the maximum number of savepoints we're
* allowed to store simultaneously, drop the oldest savepoint;
* otherwise, simply increment the savepoint counter
*/
if (savept_cnt_ == max_savepts_)
{
/* we have the maximum number of savepoints; discard the oldest */
drop_oldest_savept(vmg0_);
}
/* count the new savepoint */
++savept_cnt_;
/* notify the objects that we're starting a new savepoint */
G_obj_table->notify_new_savept();
}
/*
* Discard the oldest savepoint
*/
void CVmUndo::drop_oldest_savept(VMG0_)
{
/* if there are no savepoints, there's nothing to do */
if (savept_cnt_ == 0)
return;
/* decrement the savepoint count, now that this one is gone */
--savept_cnt_;
/* forget the oldest lead pointer */
if (oldest_first_ != 0)
{
/*
* discard records from the oldest lead pointer to the next
* oldest lead pointer
*/
CVmUndoMeta *meta;
for (meta = oldest_first_, inc_rec_ptr(&meta) ;
meta != oldest_first_->link.next_first && meta != next_free_ ; )
{
/* discard this entry, if it still exists */
if (meta->rec.obj != VM_INVALID_OBJ)
vm_objp(vmg_ meta->rec.obj)->discard_undo(vmg_ &meta->rec);
/* advance to the next record */
inc_rec_ptr(&meta);
}
/* advance the oldest pointer to the next savepoint's first record */
oldest_first_ = oldest_first_->link.next_first;
/* there's now nothing before this one */
if (oldest_first_ != 0)
oldest_first_->link.prev_first = 0;
}
/* if we don't have an oldest, we also don't have a current */
if (oldest_first_ == 0)
cur_first_ = 0;
}
/*
* Drop all undo information
*/
void CVmUndo::drop_undo(VMG0_)
{
/* delete each savepoint until we have none left */
while (savept_cnt_ != 0)
drop_oldest_savept(vmg0_);
/* reset the savepoint number */
cur_savept_ = 0;
/* we have no "firsts" */
cur_first_ = 0;
oldest_first_ = 0;
/* start allocating from the start of the array */
next_free_ = rec_arr_;
}
/*
* Allocate an undo record. If we run out of free records, delete
* savepoints, starting with the oldest savepoint, until we have a free
* record.
*/
CVmUndoMeta *CVmUndo::alloc_rec(VMG0_)
{
/*
* keep trying until we find an entry or run out of savepoints to
* delete
*/
for (;;)
{
/*
* If we have no savepoints at all, all records are free.
* Otherwise, if the next free pointer hasn't bumped up against
* the oldest allocated record yet, we can allocate another
* record.
*/
if (savept_cnt_ == 0 || next_free_ != oldest_first_)
{
CVmUndoMeta *ret;
/* remember the current free record */
ret = next_free_;
/*
* advance to the next record, wrapping if we reach the end
* of the array (since we treat the array as circular)
*/
inc_rec_ptr(&next_free_);
/* return the record */
return ret;
}
/*
* If we have at least one old savepoint, discard the oldest
* savepoint, which may free up some records, and try again;
* otherwise, give up.
*/
if (savept_cnt_ > 1)
{
/*
* we have at least one old savepoint we can discard - get
* rid of it and try again
*/
drop_oldest_savept(vmg0_);
}
else
{
/*
* we are down to our last savepoint (or none at all) - it's
* no longer valid (since we can't keep it complete due to
* the lack of available records), so delete it and return
* failure
*/
drop_oldest_savept(vmg0_);
return 0;
}
}
}
/*
* Add a new record with a property ID key
*/
void CVmUndo::add_new_record_prop_key(VMG_ vm_obj_id_t obj, vm_prop_id_t key,
const vm_val_t *val)
{
CVmUndoRecord *rec;
/* allocate the new record */
rec = add_new_record(vmg_ obj);
/* if we successfully allocated a record, set it up */
if (rec != 0)
{
/* set the object */
rec->obj = obj;
/* set the key */
rec->id.prop = key;
/* set the value */
rec->oldval = *val;
}
}
/*
* Add a new record with an integer key
*/
void CVmUndo::add_new_record_int_key(VMG_ vm_obj_id_t obj, uint32_t key,
const vm_val_t *val)
{
CVmUndoRecord *rec;
/* allocate the new record */
rec = add_new_record(vmg_ obj);
/* if we successfully allocated a record, set it up */
if (rec != 0)
{
/* set the object */
rec->obj = obj;
/* set the key */
rec->id.intval = key;
/* set the value */
rec->oldval = *val;
}
}
/*
* Add a new record with a pointer key
*/
int CVmUndo::add_new_record_ptr_key(VMG_ vm_obj_id_t obj, void *key,
const vm_val_t *val)
{
CVmUndoRecord *rec;
/* allocate the new record */
rec = add_new_record(vmg_ obj);
/* if we successfully allocated a record, set it up */
if (rec != 0)
{
/* set the object */
rec->obj = obj;
/* set the key */
rec->id.ptrval = key;
/* set the value */
rec->oldval = *val;
}
/* return an indication as to whether the record was created */
return (rec != 0);
}
/*
* Add a new undo record
*/
CVmUndoRecord *CVmUndo::add_new_record(VMG_ vm_obj_id_t controlling_obj)
{
CVmUndoMeta *meta;
/* if there is not an active savepoint, do not keep undo */
if (savept_cnt_ == 0)
return 0;
/*
* if the object was created after the current savepoint was created,
* there is no need to keep undo for it during this savepoint, since
* rolling back to the savepoint will roll back to a point at which
* the object didn't even exist
*/
if (!G_obj_table->is_obj_in_undo(controlling_obj))
return 0;
/* allocate a new record */
meta = alloc_rec(vmg0_);
/* return the undo record, if we succeeded */
return (meta == 0 ? 0 : &meta->rec);
}
/*
* Apply undo to the most recent savepoint.
*/
void CVmUndo::undo_to_savept(VMG0_)
{
CVmUndoMeta *meta;
/* if we don't have any savepoints, there's nothing to do */
if (savept_cnt_ == 0)
return;
/*
* Starting with the most recently-added record, apply each record
* in sequence until we reach the first savepoint in the undo list.
*/
meta = next_free_;
for (;;)
{
/*
* move to the previous record, wrapping to the end of the array
* at the first record (since we treat the array as circular)
*/
if (meta == rec_arr_)
meta = rec_arr_ + rec_arr_size_;
--meta;
/*
* if we're at the first record in the current savepoint, we're
* done
*/
if (meta == cur_first_)
break;
/* apply this undo record */
G_obj_table->apply_undo(vmg_ &meta->rec);
}
/*
* Unwind the undo stack -- get the first record in the previous
* savepoint from the link pointer.
*/
cur_first_ = cur_first_->link.prev_first;
/*
* there's nothing following the current savepoint any more -- the
* savepoint we just applied is gone now
*/
if (cur_first_ != 0)
cur_first_->link.next_first = 0;
else
oldest_first_ = 0;
/* that's one less savepoint */
--savept_cnt_;
/* make the previous savepoint current */
--cur_savept_;
if (cur_savept_ == 0)
cur_savept_ = VM_SAVEPT_MAX;
/* the savepoint link we just removed is now the next free record */
next_free_ = meta;
/*
* notify objects that a new savepoint is in effect - the savepoint
* isn't new in the sense of being newly created, but in the sense of
* being a different savepoint than was previously in effect
*/
G_obj_table->notify_new_savept();
}
/*
* Garbage collection: mark referenced objects. This goes through all
* of the undo records; for each undo record, we have the object that
* owns the undo record mark as referenced any object to which the
* record refers.
*/
void CVmUndo::gc_mark_refs(VMG0_)
{
CVmUndoMeta *cur;
CVmUndoMeta *next_link;
/* if we don't have any records, there's nothing to do */
if (oldest_first_ == 0)
return;
/* the first record is a linking record */
next_link = oldest_first_;
/* start at the first record */
cur = oldest_first_;
/*
* Go through all undo records, from the oldest to the newest. Note
* that we must keep track of each "link" record, because these are
* not ordinary undo records and must be handled differently.
*/
for (;;)
{
/* check to see if this is a linking record or an ordinary record */
if (cur == next_link)
{
/*
* this is a linking record - simply note the next linking
* record and otherwise ignore this record
*/
next_link = cur->link.next_first;
}
else if (cur->rec.obj != VM_INVALID_OBJ)
{
/*
* It's an ordinary undo record -- mark its references.
* Note that the fact that an object has undo records does
* not mean that the object is reachable -- this is
* effectively a weak link to the object, because if it's
* not reachable through other means, there's no need to
* keep any undo information for it; so, we don't mark the
* owner object itself as reachable at this point.
*/
G_obj_table->mark_obj_undo_rec(vmg_ cur->rec.obj, &cur->rec);
}
/* advance to the next record, wrapping at the end of the array */
++cur;
if (cur == rec_arr_ + rec_arr_size_)
cur = rec_arr_;
/* stop if we've reached the last record */
if (cur == next_free_)
break;
}
}
/*
* Garbage collection: delete obsolete weak references. This goes
* through all of the undo records; for each undo record, if the object
* that owns the record is unreachable, we'll delete the undo record;
* otherwise, we'll tell the object that owns the record to clean up the
* record if it contains an unreachable weak reference.
*/
void CVmUndo::gc_remove_stale_weak_refs(VMG0_)
{
CVmUndoMeta *cur;
CVmUndoMeta *next_link;
/* if we don't have any records, there's nothing to do */
if (oldest_first_ == 0)
return;
/* the first record is a linking record */
next_link = oldest_first_;
/* start at the first record */
cur = oldest_first_;
/*
* Go through all undo records, from the oldest to the newest. Note
* that we must keep track of each "link" record, because these are
* not ordinary undo records and must be handled differently.
*/
for (;;)
{
/* check to see if this is a linking record or an ordinary record */
if (cur == next_link)
{
/*
* this is a linking record - simply note the next linking
* record and otherwise ignore this record
*/
next_link = cur->link.next_first;
}
else if (cur->rec.obj != VM_INVALID_OBJ)
{
/*
* It's an ordinary undo record -- delete its stale
* references. If the record owner is itself about to be
* deleted, don't bother with the object, but rather delete
* the entire undo record -- undo records themselves only
* weakly reference their owning objects.
*/
if (!G_obj_table->is_obj_deletable(cur->rec.obj))
{
/* it's not ready for deletion - clean up its weak refs */
G_obj_table->remove_obj_stale_undo_weak_ref(
vmg_ cur->rec.obj, &cur->rec);
}
else
{
/*
* it's no longer reachable - delete the undo record by
* setting the owning object to 'invalid'
*/
cur->rec.obj = VM_INVALID_OBJ;
}
}
/* advance to the next record, wrapping at the end of the array */
++cur;
if (cur == rec_arr_ + rec_arr_size_)
cur = rec_arr_;
/* stop if we've reached the last record */
if (cur == next_free_)
break;
}
}
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