var readStateMachine = function()

in JSLib/src/cache.js [1109:1187]
43 lines of code
15 McCabe index (conditional complexity)

        var readStateMachine = function (operation, opTargetState, cacheState, data) {
            /// <summary>State machine describing the behavior of a read operation.</summary>
            /// <param name="operation" type="DataCacheOperation">Operation being run.</param>
            /// <param name="opTargetState" type="Object">Operation state to transition to.</param>
            /// <param name="cacheState" type="Object">Current cache state.</param>
            /// <param name="data" type="Object" optional="true">Additional data passed to the state.</param>
            /// <remarks>
            /// Read operations have a higher priority than prefetch operations, but lower than
            /// clear operations. They will preempt any prefetch operation currently running
            /// but will be interrupted by a clear operation.
            ///
            /// If a clear operation starts executing then all the currently running
            /// read operations are canceled. Read operations that haven't started yet will
            /// wait in the start state until the destory operation finishes.
            /// </remarks>

            // Handle cancelation
            if (!cancelStateMachine(operation, opTargetState, cacheState, data)) {

                var transition = operation.transition;

                // Handle preemption
                if (cacheState !== CACHE_STATE_READ && opTargetState !== OPERATION_STATE_START) {
                    if (cacheState === CACHE_STATE_DESTROY) {
                        if (opTargetState !== OPERATION_STATE_START) {
                            operation.cancel();
                        }
                    } else if (cacheState !== CACHE_STATE_WRITE) {
                        // Signal the cache that a read operation is running.
                        djsassert(state == CACHE_STATE_IDLE || state === CACHE_STATE_PREFETCH, "DataCache.readStateMachine() - cache is not on the read or idle state.");
                        changeState(CACHE_STATE_READ);
                    }

                    return true;
                }

                switch (opTargetState) {
                    case OPERATION_STATE_START:
                        // Initial state of the operation.
                        // Wait until the cache is idle or prefetching.
                        if (cacheState === CACHE_STATE_IDLE || cacheState === CACHE_STATE_PREFETCH) {
                            // Signal the cache that a read operation is running.
                            changeState(CACHE_STATE_READ);
                            if (operation.c > 0) {
                                // Snap the requested range to a page boundary.
                                var range = snapToPageBoundaries(operation.i, operation.c, pageSize);
                                transition(READ_STATE_LOCAL, range.i);
                            } else {
                                transition(READ_STATE_DONE, operation);
                            }
                        }
                        break;

                    case READ_STATE_DONE:
                        // State that determines if the operation can be resolved or has to
                        // continue processing.
                        // Data is expected to be the read page.
                        appendPage(operation, data);
                        var len = operation.d.length;
                        // Are we done?
                        if (operation.c === len || data.c < pageSize) {
                            // Update the stats, request for a prefetch operation.
                            stats.cacheReads++;
                            prefetch(data.i + data.c);
                            // Terminate the operation.
                            operation.complete();
                        } else {
                            // Continue processing the operation.
                            transition(READ_STATE_LOCAL, data.i + pageSize);
                        }
                        break;

                    default:
                        return readSaveStateMachine(operation, opTargetState, cacheState, data, false);
                }
            }

            return true;
        };