001package votorola.g.hold; // Copyright 2005-2007, Michael Allan. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Votorola Software"), to deal in the Votorola Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicence, and/or sell copies of the Votorola Software, and to permit persons to whom the Votorola Software is furnished to do so, subject to the following conditions: The preceding copyright notice and this permission notice shall be included in all copies or substantial portions of the Votorola Software. THE VOTOROLA SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE VOTOROLA SOFTWARE OR THE USE OR OTHER DEALINGS IN THE VOTOROLA SOFTWARE. 002 003import votorola.g.lang.*; 004 005 006/** An unwindable spool of {@linkplain Hold holds}. It contols and implements the closure 007 * of an object - the "unwinding" of its state. As an object takes hold of resources 008 * that later need to be released, it constructs a {@linkplain Hold Hold} for each, and 009 * winds it onto a spool. At closure the object, the spool is unwound, and each hold is 010 * {@linkplain Hold#release() released}. 011 * 012 * <p>An example is listener registration. This is state that often needs to be unwound, 013 * in order to prevent memory leaks. Using a spool, both registration and unregistration 014 * may be coded together in line. For example:</p> 015 * 016 * <blockquote><pre> 017 * registry.addListener( C.this ); 018 * spool.add( new Hold() 019 * { 020 * public void release() { registry.removeListener( C.this ); } 021 * }); 022 * </pre></blockquote> 023 * 024 * <p>The life cycle of spools follows two common patterns. In one, a spool is created 025 * internally by the object, and later unwound by it (in a public close() method, for 026 * example) In the other pattern, a spool is passed to the object by a construction 027 * parameter, and later unwound by its creator (effectively destroying the object, and 028 * any others that had wound themselves onto it). The latter is the more common pattern; 029 * but the codebase [of textbender] has examples of both. In any case, once unwound, a 030 * spool is never resused.</p> 031 */ 032public interface Spool 033{ 034 035 036 /** A common instance of a null catcher. 037 */ 038 public static final Catcher0R<Hold> CATCHER_0 = Catcher0R.i(); // till we figure out how to declare Catcher0R.i() so we can use a direct reference instead 039 040 041 042 // - S p o o l ------------------------------------------------------------------------ 043 044 045 /** Adds the hold to the spool or releases it immediately. If the spool is unwinding 046 * then the hold is released immediately, otherwise it is added. 047 * 048 * @throws IllegalStateException if this contract cannot be met (e.g. if the 049 * spool runs out of space, and no other unchecked exception applies). 050 * 051 * @return true if the hold is added; false if it is released instead. 052 */ 053 public boolean add( Hold hold ); 054 055 056 057 /** Returns true if the spool is {@linkplain #unwind() unwinding} or already unwound. 058 * Once true, it never reverts to false. 059 */ 060 public boolean isUnwinding(); 061 062 063 064 /** Commences to unwind this spool. Equivalent to {@linkplain #unwind(Catcher) 065 * unwind}(CATCHER_0). 066 * 067 * @return true if unwinding commences with this call; false if it had already 068 * commenced. 069 */ 070 public boolean unwind(); 071 072 073 074 /** Commences to unwind this spool, removing and releasing each of its holds. Works 075 * in LIFO order. Once unwinding is commenced, subsequent calls to this method have 076 * no effect. 077 * 078 * @param catcher the catcher for any errors or exceptions that occur during 079 * unwinding. 080 * 081 * @return true if unwinding commences with this call; false if it had already 082 * commenced. 083 */ 084 public boolean unwind( Catcher<Hold> catcher ); 085 086 087 088}