88 lines
2.8 KiB
Zig
88 lines
2.8 KiB
Zig
//
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// Remember how a function with 'suspend' is async and calling an
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// async function without the 'async' keyword makes the CALLING
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// function async?
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//
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// fn fooThatMightSuspend(maybe: bool) void {
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// if (maybe) suspend {}
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// }
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//
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// fn bar() void {
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// fooThatMightSuspend(true); // Now bar() is async!
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// }
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//
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// But if you KNOW the function won't suspend, you can make a
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// promise to the compiler with the 'nosuspend' keyword:
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//
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// fn bar() void {
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// nosuspend fooThatMightSuspend(false);
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// }
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//
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// If the function does suspend and YOUR PROMISE TO THE COMPILER
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// IS BROKEN, the program will panic at runtime, which is
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// probably better than you deserve, you oathbreaker! >:-(
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//
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const print = @import("std").debug.print;
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pub fn main() void {
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// The main() function can not be async. But we know
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// getBeef() will not suspend with this particular
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// invocation. Please make this okay:
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var my_beef = nosuspend getBeef(0);
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print("beef? {X}!\n", .{my_beef});
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}
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fn getBeef(input: u32) u32 {
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if (input == 0xDEAD) {
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suspend {}
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}
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return 0xBEEF;
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}
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//
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// Going Deeper Into...
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// ...uNdeFiNEd beHAVi0r!
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//
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// We haven't discussed it yet, but runtime "safety" features
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// require some extra instructions in your compiled program.
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// Most of the time, you're going to want to keep these in.
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//
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// But in some programs, when data integrity is less important
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// than raw speed (some games, for example), you can compile
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// without these safety features.
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//
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// Instead of a safe panic when something goes wrong, your
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// program will now exhibit Undefined Behavior (UB), which simply
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// means that the Zig language does not (cannot) define what will
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// happen. The best case is that it will crash, but in the worst
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// case, it will continue to run with the wrong results and
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// corrupt your data or expose you to security risks.
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//
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// This program is a great way to explore UB. Once you get it
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// working, try calling the getBeef() function with the value
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// 0xDEAD so that it will invoke the 'suspend' keyword:
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//
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// getBeef(0xDEAD)
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//
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// Now when you run the program, it will panic and give you a
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// nice stack trace to help debug the problem.
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//
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// zig run exercises/090_async7.zig
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// thread 328 panic: async function called...
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// ...
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//
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// But see what happens when you turn off safety checks by using
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// ReleaseFast mode:
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//
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// zig run -O ReleaseFast exercises/090_async7.zig
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// beef? 0!
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//
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// This is the wrong result. On your computer, you may get a
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// different answer or it might crash! What exactly will happen
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// is UNDEFINED. Your computer is now like a wild animal,
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// reacting to bits and bytes of raw memory with the base
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// instincts of the CPU. It is both terrifying and exhilarating.
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//
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