Services: Integrate into standard scripts

src/execution/base.ts

@@ -102,4 +102,37 @@ export abstract class BaseExecutionWithCommand<
    * needed to run at all.
    */
   readonly servicesNotNeeded = this._servicesNotNeeded.promise;
+
+  /**
+   * Resolves when any of the services this script depends on have terminated
+   * (see {@link ServiceScriptExecution.terminated} for exact definiton).
+   */
+  readonly anyServiceTerminated = Promise.race(
+    this._config.services.map(
+      (service) => this._executor.getExecution(service).terminated
+    )
+  );
+
+  /**
+   * Ensure that all of the services this script depends on are running.
+   */
+  protected async _startServices(): Promise<Result<void, Failure[]>> {
+    if (this._config.services.length > 0) {
+      const results = await Promise.all(
+        this._config.services.map((service) =>
+          this._executor.getExecution(service).start()
+        )
+      );
+      const errors: Failure[] = [];
+      for (const result of results) {
+        if (!result.ok) {
+          errors.push(...result.error);
+        }
+      }
+      if (errors.length > 0) {
+        return {ok: false, error: errors};
+      }
+    }
+    return {ok: true, value: undefined};
+  }
 }

src/execution/service.ts

@@ -6,16 +6,31 @@
 
 import {BaseExecutionWithCommand} from './base.js';
 import {Fingerprint} from '../fingerprint.js';
+import {Deferred} from '../util/deferred.js';
 
 import type {ExecutionResult} from './base.js';
 import type {ServiceScriptConfig} from '../config.js';
 import type {Executor} from '../executor.js';
 import type {Logger} from '../logging/logger.js';
+import type {Failure} from '../event.js';
+import type {Result} from '../error.js';
 
 /**
  * Execution for a {@link ServiceScriptConfig}.
  */
 export class ServiceScriptExecution extends BaseExecutionWithCommand<ServiceScriptConfig> {
+  private readonly _terminated = new Deferred<Result<void, Failure>>();
+
+  /**
+   * Resolves as "ok" when this script decides it is no longer needed, and
+   * either has begun shutting down, or never needed to start in the first
+   * place.
+   *
+   * Resolves with an error if this service exited unexpectedly, or if any of
+   * its own service dependencies exited unexpectedly.
+   */
+  readonly terminated = this._terminated.promise;
+
   constructor(
     config: ServiceScriptConfig,
     executor: Executor,
@@ -42,5 +57,11 @@ export class ServiceScriptExecution extends BaseExecutionWithCommand<ServiceScri
     return {ok: true, value: fingerprint};
   }
 
-  // TODO(aomarks) Implement service starting/stopping.
+  /**
+   * Start this service if it isn't already started.
+   */
+  start(): Promise<Result<void, Failure[]>> {
+    // TODO(aomarks) Implement service starting/stopping.
+    throw new Error('Not implemented');
+  }
 }

src/execution/standard.ts

@@ -24,7 +24,7 @@ import type {StandardScriptConfig} from '../config.js';
 import type {FingerprintString} from '../fingerprint.js';
 import type {Logger} from '../logging/logger.js';
 import type {Cache, CacheHit} from '../caching/cache.js';
-import type {StartCancelled} from '../event.js';
+import type {Failure, StartCancelled} from '../event.js';
 import type {AbsoluteEntry} from '../util/glob.js';
 import type {FileManifestEntry, FileManifestString} from '../util/manifest.js';
 
@@ -316,6 +316,41 @@ export class StandardScriptExecution extends BaseExecutionWithCommand<StandardSc
         return {ok: false, error: this._startCancelledEvent};
       }
 
+      let earlyServiceTermination: Failure | undefined;
+      if (this._config.services.length > 0) {
+        const servicesStarted = await this._startServices();
+        if (!servicesStarted.ok) {
+          return servicesStarted;
+        }
+
+        void this.anyServiceTerminated.then((result) => {
+          if (this._state === 'after-running') {
+            // This is expected after we're done.
+            return;
+          }
+          if (result.ok) {
+            // This should never happen and indicates an internal error. The
+            // service believed that nothing was depending on it anymore, but
+            // we're still running.
+            earlyServiceTermination = {
+              script: this._config,
+              type: 'failure',
+              reason: 'unknown-error-thrown',
+              error: new Error(
+                'Internal error: service dependency terminated unexpectedly'
+              ),
+            };
+          } else {
+            // The service knows it exited too early. Propagate that error.
+            earlyServiceTermination = result.error;
+          }
+          // Stop running. If a service we depend on is down, then we know we're
+          // in an invalid state too.
+          child.kill();
+          this._executor.notifyFailure();
+        });
+      }
+
       this._state = 'running';
       this._logger.log({
         script: this._config,
@@ -353,11 +388,15 @@ export class StandardScriptExecution extends BaseExecutionWithCommand<StandardSc
 
       const result = await child.completed;
       if (result.ok) {
-        this._logger.log({
-          script: this._config,
-          type: 'success',
-          reason: 'exit-zero',
-        });
+        if (earlyServiceTermination !== undefined) {
+          return {ok: false, error: earlyServiceTermination};
+        } else {
+          this._logger.log({
+            script: this._config,
+            type: 'success',
+            reason: 'exit-zero',
+          });
+        }
       } else {
         // This failure will propagate to the Executor eventually anyway, but
         // asynchronously.
@@ -378,7 +417,12 @@ export class StandardScriptExecution extends BaseExecutionWithCommand<StandardSc
     this._state = 'after-running';
 
     if (!childResult.ok) {
-      return {ok: false, error: [childResult.error]};
+      return {
+        ok: false,
+        error: Array.isArray(childResult.error)
+          ? childResult.error
+          : [childResult.error],
+      };
     }
 
     // Optimization: early signal that services are no longer needed while we're