mirror of
https://github.com/scratchfoundation/scratch-vm.git
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134 lines
3.5 KiB
JavaScript
134 lines
3.5 KiB
JavaScript
/**
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* A thread is a running stack context and all the metadata needed.
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* @param {?string} firstBlock First block to execute in the thread.
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* @constructor
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*/
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function Thread (firstBlock) {
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/**
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* ID of top block of the thread
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* @type {!string}
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*/
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this.topBlock = firstBlock;
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/**
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* Stack for the thread. When the sequencer enters a control structure,
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* the block is pushed onto the stack so we know where to exit.
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* @type {Array.<string>}
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*/
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this.stack = [];
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/**
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* Stack frames for the thread. Store metadata for the executing blocks.
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* @type {Array.<Object>}
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*/
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this.stackFrames = [];
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/**
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* Status of the thread, one of three states (below)
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* @type {number}
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*/
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this.status = 0; /* Thread.STATUS_RUNNING */
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}
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/**
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* Thread status for initialized or running thread.
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* This is the default state for a thread - execution should run normally,
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* stepping from block to block.
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* @const
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*/
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Thread.STATUS_RUNNING = 0;
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/**
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* Thread status for a yielded thread.
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* Threads are in this state when a primitive has yielded; execution is paused
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* until the relevant primitive unyields.
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* @const
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*/
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Thread.STATUS_YIELD = 1;
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/**
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* Thread status for a single-frame yield.
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* @const
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*/
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Thread.STATUS_YIELD_FRAME = 2;
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/**
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* Thread status for a finished/done thread.
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* Thread is in this state when there are no more blocks to execute.
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* @const
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*/
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Thread.STATUS_DONE = 3;
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/**
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* Push stack and update stack frames appropriately.
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* @param {string} blockId Block ID to push to stack.
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*/
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Thread.prototype.pushStack = function (blockId) {
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this.stack.push(blockId);
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// Push an empty stack frame, if we need one.
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// Might not, if we just popped the stack.
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if (this.stack.length > this.stackFrames.length) {
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this.stackFrames.push({
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reported: {}, // Collects reported input values.
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waitingReporter: null, // Name of waiting reporter.
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executionContext: {} // A context passed to block implementations.
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});
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}
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};
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/**
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* Pop last block on the stack and its stack frame.
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* @return {string} Block ID popped from the stack.
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*/
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Thread.prototype.popStack = function () {
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this.stackFrames.pop();
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return this.stack.pop();
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};
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/**
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* Get top stack item.
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* @return {?string} Block ID on top of stack.
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*/
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Thread.prototype.peekStack = function () {
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return this.stack[this.stack.length - 1];
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};
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/**
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* Get top stack frame.
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* @return {?Object} Last stack frame stored on this thread.
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*/
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Thread.prototype.peekStackFrame = function () {
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return this.stackFrames[this.stackFrames.length - 1];
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};
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/**
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* Get stack frame above the current top.
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* @return {?Object} Second to last stack frame stored on this thread.
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*/
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Thread.prototype.peekParentStackFrame = function () {
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return this.stackFrames[this.stackFrames.length - 2];
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};
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/**
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* Push a reported value to the parent of the current stack frame.
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* @param {!Any} value Reported value to push.
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*/
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Thread.prototype.pushReportedValue = function (value) {
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var parentStackFrame = this.peekParentStackFrame();
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if (parentStackFrame) {
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var waitingReporter = parentStackFrame.waitingReporter;
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parentStackFrame.reported[waitingReporter] = value;
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parentStackFrame.waitingReporter = null;
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}
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};
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/**
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* Set thread status.
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* @param {number} status Enum representing thread status.
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*/
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Thread.prototype.setStatus = function (status) {
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this.status = status;
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};
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module.exports = Thread;
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