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| /** | |
| * This function ensures there's a single instance of a given effectful function | |
| * running at a time. If the function is called while it's already running, | |
| * the arguments are combined and the function is called again with the combined | |
| * arguments. | |
| */ | |
| export function oneAtATime<Args extends readonly unknown[], Return>( | |
| fn: (...args: Args) => Promise<Return>, | |
| combineArgs: (args: Args, nextArgs: Args) => Args = (_, newArgs) => newArgs, | |
| ): (...args: Args) => Promise<Return> { | |
| let state: | |
| | { type: "running" } | |
| | { | |
| type: "pending"; | |
| nextArgs: Args; | |
| promiseResolvers: PromiseWithResolvers<Return>; | |
| } | |
| | { type: "idle" } = { type: "idle" }; | |
| const onFinally = () => { | |
| if (state.type === "idle") { | |
| return; | |
| } | |
| if (state.type === "running") { | |
| state = { type: "idle" }; | |
| return; | |
| } | |
| const { promiseResolvers, nextArgs } = state; | |
| state = { type: "running" }; | |
| void Promise.resolve() | |
| .then(() => fn(...nextArgs)) | |
| .then(promiseResolvers.resolve, promiseResolvers.reject) | |
| .finally(onFinally); | |
| }; | |
| return (...args): Promise<Return> => { | |
| if (state.type === "pending") { | |
| state.nextArgs = combineArgs(state.nextArgs, args); | |
| return state.promiseResolvers.promise; | |
| } | |
| if (state.type === "running") { | |
| state = { | |
| type: "pending", | |
| nextArgs: args, | |
| promiseResolvers: Promise.withResolvers<Return>(), | |
| }; | |
| return state.promiseResolvers.promise; | |
| } | |
| state = { type: "running" }; | |
| return Promise.resolve() | |
| .then(() => fn(...args)) | |
| .finally(onFinally); | |
| }; | |
| } |
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