feat: automatically profile when --require'd (#8)

Author: ofrobots

ts/src/index.ts

@@ -13,6 +13,11 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+import {writeFileSync} from 'fs';
+import {gzipSync} from 'zlib';
+
+import {perftools} from '../../proto/profile';
+
 import * as heapProfiler from './heap-profiler';
 import * as timeProfiler from './time-profiler';
 
@@ -28,3 +33,16 @@ export const heap = {
   stop: heapProfiler.stop,
   profile: heapProfiler.profile,
 };
+
+// If loaded with --require, start profiling.
+if (module.parent && module.parent.id === 'internal/preload') {
+  const stop = time.start();
+  process.on('exit', () => {
+    // The process is going to terminate imminently. All work here needs to
+    // be synchronous.
+    const profile = stop();
+    const buffer = perftools.profiles.Profile.encode(profile).finish();
+    const compressed = gzipSync(buffer);
+    writeFileSync(`pprof-profile-${process.pid}.pb.gz`, compressed);
+  });
+}

ts/src/time-profiler.ts

@@ -22,6 +22,8 @@ import {setSamplingInterval, startProfiling, stopProfiling} from './time-profile
 
 let profiling = false;
 
+const DEFAULT_INTERVAL_MICROS: Microseconds = 1000;
+
 type Microseconds = number;
 type Milliseconds = number;
 
@@ -35,14 +37,16 @@ export interface TimeProfilerOptions {
 }
 
 export async function profile(options: TimeProfilerOptions) {
-  const stop =
-      start(options.intervalMicros || 1000, options.name, options.sourceMapper);
+  const stop = start(
+      options.intervalMicros || DEFAULT_INTERVAL_MICROS, options.name,
+      options.sourceMapper);
   await delay(options.durationMillis);
   return stop();
 }
 
 export function start(
-    intervalMicros: Microseconds, name?: string, sourceMapper?: SourceMapper) {
+    intervalMicros: Microseconds = DEFAULT_INTERVAL_MICROS, name?: string,
+    sourceMapper?: SourceMapper) {
   if (profiling) {
     throw new Error('already profiling');
   }