/**
* Supervisor manages restart logic with exponential backoff.
* Extracted for testability - no child process or I/O dependencies.
*/
export interface SupervisorConfig {
maxRestarts: number;
initialDelayMs: number;
maxDelayMs: number;
successThresholdMs: number;
}
export const DEFAULT_CONFIG: SupervisorConfig = {
maxRestarts: 10,
initialDelayMs: 1000,
maxDelayMs: 30000,
successThresholdMs: 30000,
};
export class Supervisor {
private restartCount = 0;
private delay: number;
private startTime = 0;
constructor(private config: SupervisorConfig = DEFAULT_CONFIG) {
this.delay = config.initialDelayMs;
}
/** Call when process starts */
onStart(): void {
this.startTime = Date.now();
}
/**
* Call when process exits. Returns action to take.
* @param code - exit code (0 = normal, null = signal, other = crash)
*/
onExit(code: number | null): { action: 'stop' | 'restart' | 'give-up'; delay?: number; restartCount?: number } {
// Normal exit or signal - stop
if (code === 0 || code === null) {
return { action: 'stop' };
}
// Reset if ran successfully for a while
const runDuration = Date.now() - this.startTime;
if (runDuration > this.config.successThresholdMs) {
this.restartCount = 0;
this.delay = this.config.initialDelayMs;
}
this.restartCount++;
if (this.restartCount > this.config.maxRestarts) {
return { action: 'give-up', restartCount: this.restartCount };
}
const currentDelay = this.delay;
this.delay = Math.min(this.delay * 2, this.config.maxDelayMs);
return { action: 'restart', delay: currentDelay, restartCount: this.restartCount };
}
/** Get current state for testing/logging */
getState(): { restartCount: number; delay: number } {
return { restartCount: this.restartCount, delay: this.delay };
}
}
