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    }
}

/**
 * Converts thenables to Q promises.
 * @param promise thenable promise
 * @returns a Q promise
 */
function coerce(promise) {
    var deferred = defer();
    nextTick(function () {
        try {
            promise.then(deferred.resolve, deferred.reject, deferred.notify);
        } catch (exception) {
            deferred.reject(exception);
        }
    });
    return deferred.promise;
}

/**
 * Annotates an object such that it will never be
 * transferred away from this process over any promise
 * communication channel.
 * @param object
 * @returns promise a wrapping of that object that
 * additionally responds to the "isDef" message
 * without a rejection.
 */
Q.master = master;
function master(object) {
    return makePromise({
        "isDef": function () {}
    }, function fallback(op, args) {
        return dispatch(object, op, args);
    }, function () {
        return valueOf(object);
    });
}

/**
 * Registers an observer on a promise.
 *
 * Guarantees:
 *
 * 1. that fulfilled and rejected will be called only once.
 * 2. that either the fulfilled callback or the rejected callback will be
 *    called, but not both.
 * 3. that fulfilled and rejected will not be called in this turn.
 *
 * @param value      promise or immediate reference to observe
 * @param fulfilled  function to be called with the fulfilled value
 * @param rejected   function to be called with the rejection exception
 * @param progressed function to be called on any progress notifications
 * @return promise for the return value from the invoked callback
 */
Q.when = when;
function when(value, fulfilled, rejected, progressed) {
    var deferred = defer();
    var done = false;   // ensure the untrusted promise makes at most a
                        // single call to one of the callbacks

    function _fulfilled(value) {
        try {
            return typeof fulfilled === "function" ? fulfilled(value) : value;
        } catch (exception) {
            return reject(exception);
        }
    }

    function _rejected(exception) {
        if (typeof rejected === "function") {
            makeStackTraceLong(exception, resolvedValue);
            try {
                return rejected(exception);
            } catch (newException) {
                return reject(newException);
            }
        }
        return reject(exception);
    }

    function _progressed(value) {
        return typeof progressed === "function" ? progressed(value) : value;
    }

    var resolvedValue = resolve(value);
    nextTick(function () {
        resolvedValue.promiseDispatch(function (value) {
            if (done) {
                return;
            }
            done = true;

            deferred.resolve(_fulfilled(value));
        }, "when", [function (exception) {
            if (done) {
                return;
            }
            done = true;

            deferred.resolve(_rejected(exception));
        }]);
    });

    // Progress propagator need to be attached in the current tick.
    resolvedValue.promiseDispatch(void 0, "when", [void 0, function (value) {
        var newValue;
        var threw = false;
        try {
            newValue = _progressed(value);
        } catch (e) {
            threw = true;
            if (Q.onerror) {
                Q.onerror(e);
            } else {
                throw e;
            }
        }

        if (!threw) {