"use strict"; const {Fragment: _Fragment, jsx: _jsx, jsxs: _jsxs} = arguments[0]; const {useMDXComponents: _provideComponents} = arguments[0]; function _createMdxContent(props) { const _components = { a: "a", code: "code", div: "div", h2: "h2", li: "li", ol: "ol", p: "p", path: "path", pre: "pre", span: "span", strong: "strong", svg: "svg", ul: "ul", ..._provideComponents(), ...props.components }; return _jsxs(_Fragment, { children: [_jsxs(_components.div, { "data-callout": true, "data-callout-type": "definition", children: ["\n", _jsx(_components.div, { "data-callout-title": true, children: "Definition" }), "\n", _jsxs(_components.div, { "data-callout-body": true, children: ["\n", _jsxs(_components.p, { children: [_jsx(_components.code, { className: "language-auto", children: "Future" }), " is a Java interface representing the result of a computation that may become available later."] }), "\n"] }), "\n"] }), "\n", _jsxs(_components.p, { children: ["Strictly speaking, ", _jsx(_components.code, { className: "language-auto", children: "Future" }), " is an ", _jsx(_components.strong, { children: "interface" }), ", not a concrete class."] }), "\n", _jsxs(_components.h2, { id: "main-idea", children: [_jsx(_components.a, { className: "heading-link", href: "#main-idea", children: _jsx(_components.svg, { xmlns: "http:www.w3.org/2000/svg", fill: "#ab2b65", viewBox: "0 0 20 20", className: "w-5 h-5", children: _jsx(_components.path, { fillRule: "evenodd", clipRule: "evenodd", d: "M9.493 2.853a.75.75 0 00-1.486-.205L7.545 6H4.198a.75.75 0 000 1.5h3.14l-.69 5H3.302a.75.75 0 000 1.5h3.14l-.435 3.148a.75.75 0 001.486.205L7.955 14h2.986l-.434 3.148a.75.75 0 001.486.205L12.456 14h3.346a.75.75 0 000-1.5h-3.14l.69-5h3.346a.75.75 0 000-1.5h-3.14l.435-3.147a.75.75 0 00-1.486-.205L12.045 6H9.059l.434-3.147zM8.852 7.5l-.69 5h2.986l.69-5H8.852z" }) }) }), "Main idea"] }), "\n", _jsx(_components.p, { children: "When a task is submitted to [[ExecutorService]], the caller may not want to wait immediately." }), "\n", _jsxs(_components.p, { children: ["Instead, it can receive a ", _jsx(_components.code, { className: "language-auto", children: "Future" }), " as a placeholder for the result:"] }), "\n", _jsx(_components.pre, { className: "language-java", children: _jsx(_components.code, { className: "language-java code-highlight", children: _jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token class-name", children: "Future" }), _jsxs(_components.span, { className: "token generics", children: [_jsx(_components.span, { className: "token punctuation", children: "<" }), _jsx(_components.span, { className: "token class-name", children: "Integer" }), _jsx(_components.span, { className: "token punctuation", children: ">" })] }), " future ", _jsx(_components.span, { className: "token operator", children: "=" }), " pool", _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "submit" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), " ", _jsx(_components.span, { className: "token operator", children: "->" }), " ", _jsx(_components.span, { className: "token number", children: "42" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] }) }) }), "\n", _jsx(_components.p, { children: "Later, the program can ask whether the task is done, wait for the result, or cancel it." }), "\n", _jsxs(_components.h2, { id: "common-methods", children: [_jsx(_components.a, { className: "heading-link", href: "#common-methods", children: _jsx(_components.svg, { xmlns: "http:www.w3.org/2000/svg", fill: "#ab2b65", viewBox: "0 0 20 20", className: "w-5 h-5", children: _jsx(_components.path, { fillRule: "evenodd", clipRule: "evenodd", d: "M9.493 2.853a.75.75 0 00-1.486-.205L7.545 6H4.198a.75.75 0 000 1.5h3.14l-.69 5H3.302a.75.75 0 000 1.5h3.14l-.435 3.148a.75.75 0 001.486.205L7.955 14h2.986l-.434 3.148a.75.75 0 001.486.205L12.456 14h3.346a.75.75 0 000-1.5h-3.14l.69-5h3.346a.75.75 0 000-1.5h-3.14l.435-3.147a.75.75 0 00-1.486-.205L12.045 6H9.059l.434-3.147zM8.852 7.5l-.69 5h2.986l.69-5H8.852z" }) }) }), "Common methods"] }), "\n", _jsxs(_components.ul, { children: ["\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "get()" }), ": wait until the result is ready, then return it"] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "get(timeout, unit)" }), ": wait only up to a time limit"] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "isDone()" }), ": check whether the computation has finished"] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "cancel(boolean mayInterruptIfRunning)" }), ": try to cancel the task"] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "isCancelled()" }), ": check whether cancellation succeeded"] }), "\n"] }), "\n", _jsxs(_components.h2, { id: "example", children: [_jsx(_components.a, { className: "heading-link", href: "#example", children: _jsx(_components.svg, { xmlns: "http:www.w3.org/2000/svg", fill: "#ab2b65", viewBox: "0 0 20 20", className: "w-5 h-5", children: _jsx(_components.path, { fillRule: "evenodd", clipRule: "evenodd", d: "M9.493 2.853a.75.75 0 00-1.486-.205L7.545 6H4.198a.75.75 0 000 1.5h3.14l-.69 5H3.302a.75.75 0 000 1.5h3.14l-.435 3.148a.75.75 0 001.486.205L7.955 14h2.986l-.434 3.148a.75.75 0 001.486.205L12.456 14h3.346a.75.75 0 000-1.5h-3.14l.69-5h3.346a.75.75 0 000-1.5h-3.14l.435-3.147a.75.75 0 00-1.486-.205L12.045 6H9.059l.434-3.147zM8.852 7.5l-.69 5h2.986l.69-5H8.852z" }) }) }), "Example"] }), "\n", _jsx(_components.pre, { className: "language-java", children: _jsxs(_components.code, { className: "language-java code-highlight", children: [_jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token keyword", children: "import" }), " ", _jsxs(_components.span, { className: "token import", children: [_jsxs(_components.span, { className: "token namespace", children: ["java", _jsx(_components.span, { className: "token punctuation", children: "." }), "util", _jsx(_components.span, { className: "token punctuation", children: "." }), "concurrent", _jsx(_components.span, { className: "token punctuation", children: "." })] }), _jsx(_components.span, { className: "token operator", children: "*" })] }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] }), _jsx(_components.span, { className: "code-line", children: "\n" }), _jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token class-name", children: "ExecutorService" }), " pool ", _jsx(_components.span, { className: "token operator", children: "=" }), " ", _jsx(_components.span, { className: "token class-name", children: "Executors" }), _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "newFixedThreadPool" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token number", children: "2" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] }), _jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token class-name", children: "Future" }), _jsxs(_components.span, { className: "token generics", children: [_jsx(_components.span, { className: "token punctuation", children: "<" }), _jsx(_components.span, { className: "token class-name", children: "Integer" }), _jsx(_components.span, { className: "token punctuation", children: ">" })] }), " future ", _jsx(_components.span, { className: "token operator", children: "=" }), " pool", _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "submit" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), " ", _jsx(_components.span, { className: "token operator", children: "->" }), " ", _jsx(_components.span, { className: "token number", children: "6" }), " ", _jsx(_components.span, { className: "token operator", children: "*" }), " ", _jsx(_components.span, { className: "token number", children: "7" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] }), _jsx(_components.span, { className: "code-line", children: "\n" }), _jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token keyword", children: "if" }), " ", _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token operator", children: "!" }), "future", _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "isDone" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), " ", _jsx(_components.span, { className: "token punctuation", children: "{" }), "\n"] }), _jsxs(_components.span, { className: "code-line", children: [" ", _jsx(_components.span, { className: "token class-name", children: "System" }), _jsx(_components.span, { className: "token punctuation", children: "." }), "out", _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "println" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token string", children: "\"still running...\"" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] }), _jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token punctuation", children: "}" }), "\n"] }), _jsx(_components.span, { className: "code-line", children: "\n" }), _jsxs(_components.span, { className: "code-line", children: [_jsx(_components.span, { className: "token keyword", children: "int" }), " result ", _jsx(_components.span, { className: "token operator", children: "=" }), " future", _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "get" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] }), _jsxs(_components.span, { className: "code-line", children: ["pool", _jsx(_components.span, { className: "token punctuation", children: "." }), _jsx(_components.span, { className: "token function", children: "shutdown" }), _jsx(_components.span, { className: "token punctuation", children: "(" }), _jsx(_components.span, { className: "token punctuation", children: ")" }), _jsx(_components.span, { className: "token punctuation", children: ";" }), "\n"] })] }) }), "\n", _jsxs(_components.h2, { id: "what-blocks-and-what-does-not", children: [_jsx(_components.a, { className: "heading-link", href: "#what-blocks-and-what-does-not", children: _jsx(_components.svg, { xmlns: "http:www.w3.org/2000/svg", fill: "#ab2b65", viewBox: "0 0 20 20", className: "w-5 h-5", children: _jsx(_components.path, { fillRule: "evenodd", clipRule: "evenodd", d: "M9.493 2.853a.75.75 0 00-1.486-.205L7.545 6H4.198a.75.75 0 000 1.5h3.14l-.69 5H3.302a.75.75 0 000 1.5h3.14l-.435 3.148a.75.75 0 001.486.205L7.955 14h2.986l-.434 3.148a.75.75 0 001.486.205L12.456 14h3.346a.75.75 0 000-1.5h-3.14l.69-5h3.346a.75.75 0 000-1.5h-3.14l.435-3.147a.75.75 0 00-1.486-.205L12.045 6H9.059l.434-3.147zM8.852 7.5l-.69 5h2.986l.69-5H8.852z" }) }) }), "What blocks and what does not?"] }), "\n", _jsxs(_components.ul, { children: ["\n", _jsxs(_components.li, { children: ["creating the ", _jsx(_components.code, { className: "language-auto", children: "Future" }), " is usually immediate"] }), "\n", _jsx(_components.li, { children: "the submitted task runs asynchronously" }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "future.get()" }), " is the operation that typically blocks"] }), "\n"] }), "\n", _jsxs(_components.p, { children: ["This makes ", _jsx(_components.code, { className: "language-auto", children: "Future" }), " useful when we want to start work now and collect the result later."] }), "\n", _jsxs(_components.h2, { id: "relationship-with-runnable-and-callable", children: [_jsx(_components.a, { className: "heading-link", href: "#relationship-with-runnable-and-callable", children: _jsx(_components.svg, { xmlns: "http:www.w3.org/2000/svg", fill: "#ab2b65", viewBox: "0 0 20 20", className: "w-5 h-5", children: _jsx(_components.path, { fillRule: "evenodd", clipRule: "evenodd", d: "M9.493 2.853a.75.75 0 00-1.486-.205L7.545 6H4.198a.75.75 0 000 1.5h3.14l-.69 5H3.302a.75.75 0 000 1.5h3.14l-.435 3.148a.75.75 0 001.486.205L7.955 14h2.986l-.434 3.148a.75.75 0 001.486.205L12.456 14h3.346a.75.75 0 000-1.5h-3.14l.69-5h3.346a.75.75 0 000-1.5h-3.14l.435-3.147a.75.75 0 00-1.486-.205L12.045 6H9.059l.434-3.147zM8.852 7.5l-.69 5h2.986l.69-5H8.852z" }) }) }), "Relationship with ", _jsx(_components.code, { className: "language-auto", children: "Runnable" }), " and ", _jsx(_components.code, { className: "language-auto", children: "Callable" })] }), "\n", _jsxs(_components.ul, { children: ["\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "Runnable" }), ": no return value"] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "Callable" }), ": returns a value of type ", _jsx(_components.code, { className: "language-auto", children: "V" })] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "Future" }), ": handle for the eventual result of a submitted task"] }), "\n"] }), "\n", _jsx(_components.p, { children: "A common pattern is:" }), "\n", _jsxs(_components.ol, { children: ["\n", _jsxs(_components.li, { children: ["create a ", _jsx(_components.code, { className: "language-auto", children: "Callable" })] }), "\n", _jsx(_components.li, { children: "submit it to an [[ExecutorService]]" }), "\n", _jsxs(_components.li, { children: ["receive a ", _jsx(_components.code, { className: "language-auto", children: "Future" })] }), "\n", _jsxs(_components.li, { children: ["call ", _jsx(_components.code, { className: "language-auto", children: "get()" }), " later when the result is needed"] }), "\n"] }), "\n", _jsxs(_components.h2, { id: "limitations", children: [_jsx(_components.a, { className: "heading-link", href: "#limitations", children: _jsx(_components.svg, { xmlns: "http:www.w3.org/2000/svg", fill: "#ab2b65", viewBox: "0 0 20 20", className: "w-5 h-5", children: _jsx(_components.path, { fillRule: "evenodd", clipRule: "evenodd", d: "M9.493 2.853a.75.75 0 00-1.486-.205L7.545 6H4.198a.75.75 0 000 1.5h3.14l-.69 5H3.302a.75.75 0 000 1.5h3.14l-.435 3.148a.75.75 0 001.486.205L7.955 14h2.986l-.434 3.148a.75.75 0 001.486.205L12.456 14h3.346a.75.75 0 000-1.5h-3.14l.69-5h3.346a.75.75 0 000-1.5h-3.14l.435-3.147a.75.75 0 00-1.486-.205L12.045 6H9.059l.434-3.147zM8.852 7.5l-.69 5h2.986l.69-5H8.852z" }) }) }), "Limitations"] }), "\n", _jsxs(_components.p, { children: [_jsx(_components.code, { className: "language-auto", children: "Future" }), " is useful, but somewhat limited:"] }), "\n", _jsxs(_components.ul, { children: ["\n", _jsxs(_components.li, { children: [_jsx(_components.code, { className: "language-auto", children: "get()" }), " is blocking"] }), "\n", _jsx(_components.li, { children: "combining multiple futures is awkward" }), "\n", _jsx(_components.li, { children: "callbacks and pipelines are not built in" }), "\n"] }), "\n", _jsxs(_components.p, { children: ["For richer asynchronous composition, Java provides ", _jsx(_components.code, { className: "language-auto", children: "CompletableFuture" }), "."] }), "\n", _jsxs(_components.div, { "data-callout": true, "data-callout-type": "important", children: ["\n", _jsx(_components.div, { "data-callout-title": true, children: "Important" }), "\n", _jsxs(_components.div, { "data-callout-body": true, children: ["\n", _jsxs(_components.p, { children: [_jsx(_components.code, { className: "language-auto", children: "Future" }), " is best thought of as a ", _jsx(_components.strong, { children: "handle to an asynchronous result" }), ", not as the result itself."] }), "\n"] }), "\n"] })] }); } function MDXContent(props = {}) { const {wrapper: MDXLayout} = { ..._provideComponents(), ...props.components }; return MDXLayout ? _jsx(MDXLayout, { ...props, children: _jsx(_createMdxContent, { ...props }) }) : _createMdxContent(props); } return { default: MDXContent };