George Kalpakas 6ea232eb3c fix(ngcc): do not spawn more processes than intended in parallel mode (#36280)
When running in parallel mode, ngcc spawns multiple worker processed to
process the various entry-points. The number of max allowed processes is
determined by the number of CPU cores available to the OS. There is also
currently an [upper limit of 8][1]. The number of active workers is in
turn inferred by the number of [task assignments][2].

In the past, counting the entries of `ClusterMaster#taskAssignments` was
enough, because worker processes were spawned eagerly at the beginning
and corresponding entries were created in `taskAssignments`.
Since #35719 however, worker processes are spawned lazily on an as
needed basis. Because there is some delay between
[spawning a process][3] and [inserting it][4] into `taskAssignments`,
there is a short period of time when `taskAssignment.size` does not
actually represent the number of spawned processes. This can result in
spawning more than `ClusterMaster#workerCount` processes.

An example of this can be seen in #36278, where the debug logs indicate
9 worker processes had been spawned (`All 9 workers are currently busy`)
despite the hard limit of 8.

This commit fixes this by using `cluster.workers` to compute the number
of spawned worker processes. `cluster.workers` is updated synchronously
with `cluster.fork()` and thus reflects the number of spawned workers
accurately at all times.

[1]: https://github.com/angular/angular/blob/b8e9a30d3b6/packages/compiler-cli/ngcc/src/main.ts#L429
[2]: https://github.com/angular/angular/blob/b8e9a30d3b6/packages/compiler-cli/ngcc/src/execution/cluster/master.ts#L108
[3]: https://github.com/angular/angular/blob/b8e9a30d3b6/packages/compiler-cli/ngcc/src/execution/cluster/master.ts#L110
[4]: https://github.com/angular/angular/blob/b8e9a30d3b6/packages/compiler-cli/ngcc/src/execution/cluster/master.ts#L199

PR Close #36280
2020-03-27 14:12:28 -07:00
..

Angular Compatibility Compiler (ngcc)

This compiler will convert node_modules compiled with ngc, into node_modules which appear to have been compiled with ngtsc.

This conversion will allow such "legacy" packages to be used by the Ivy rendering engine.

Building

The project is built using Bazel:

yarn bazel build //packages/compiler-cli/ngcc

Unit Testing

The unit tests are built and run using Bazel:

yarn bazel test //packages/compiler-cli/ngcc/test

Integration Testing

There are tests that check the behavior of the overall executable:

yarn bazel test //packages/compiler-cli/ngcc/test:integration