src/dolda/jsvc/ContextParam.java

   1 package dolda.jsvc;
   2
   3 import java.util.*;
   4
   5 public class ContextParam<T> {
   6     private boolean bound;
   7     private T value;
   8     private final Object id = new Object();
   9     private Map<ThreadContext, T> perctx = new WeakHashMap<ThreadContext, T>();
  10     private Map<Thread, T> perthr = new WeakHashMap<Thread, T>();
  11
  12     public ContextParam(T def) {
  13         this.value = def;
  14         this.bound = true;
  15     }
  16
  17     public ContextParam() {
  18         this.bound = false;
  19     }
  20
  21     public synchronized T get() {
  22         Thread th = Thread.currentThread();
  23         if(perthr.containsKey(th))
  24             return(perthr.get(th));
  25         ThreadContext ctx = ThreadContext.current();
  26         if(perctx.containsKey(ctx))
  27             return(perctx.get(ctx));
  28         if(!bound)
  29             throw(new IllegalStateException("No value is bound to this parameter."));
  30         return(value);
  31     }
  32
  33     public synchronized T ctxset(T val) {
  34         ThreadContext ctx = ThreadContext.current();
  35         return(perctx.put(ctx, val));
  36     }
  37
  38     public static Responder let(final Responder next, Object... params) {
  39         final Map<ContextParam, Object> values = new HashMap<ContextParam, Object>();
  40         if((params.length % 2) != 0)
  41             throw(new IllegalArgumentException("SvcConfig.let takes only an even number of parameters"));
  42         for(int i = 0; i < params.length; i += 2)
  43             values.put((ContextParam)params[i], params[i + 1]);
  44
  45         return(new Responder() {
  46                 /* This can very well actually be set to something
  47                  * of the wrong type, but since the result would,
  48                  * obviously, be a ClassCastException either way,
  49                  * this way is at least the more convenient. */
  50                 @SuppressWarnings("unchecked")
  51                 public void respond(Request req) {
  52                     final Map<ContextParam, Object> old = new HashMap<ContextParam, Object>();
  53                     Thread th = Thread.currentThread();
  54                     for(Map.Entry<ContextParam, Object> val : values.entrySet()) {
  55                         ContextParam p = val.getKey();
  56                         synchronized(p) {
  57                             if(p.perthr.containsKey(th))
  58                                 old.put(p, p.perthr.get(th));
  59                             p.perthr.put(th, val.getValue());
  60                         }
  61                     }
  62                     try {
  63                         next.respond(req);
  64                     } finally {
  65                         for(Map.Entry<ContextParam, Object> val : values.entrySet()) {
  66                             ContextParam p = val.getKey();
  67                             synchronized(p) {
  68                                 if(old.containsKey(p)) {
  69                                     p.perthr.put(th, old.get(p));
  70                                 } else {
  71                                     p.perthr.remove(th);
  72                                 }
  73                             }
  74                         }
  75                     }
  76                 }
  77             });
  78     }
  79 }