Extremely slow yarn run xxxx commands on large monorepo

[etiennedupont]

Bug description

When running scripts defined in package.json using yarn run xxx on a large monorepo, there is an extremely long delay before the command is actually run. This delay is always the same and seems to depend on the size of the monorepo.

Command

Here is a simple example:

In package.json

{
  "scripts": {
    "echo": "echo ok"
  }
}

Then in shell run:

> yarn echo

.... WAITS FOR 265s .....

ok

Using time to confirm the duration:

> time yarn echo
ok
yarn echo  264.68s user 1.33s system 99% cpu 4:26.01 total

What is the current behavior?

Yarn does something using 100% of a CPU core for 265s (on my repo and machine) before actually running the command.

What is the expected behavior?

Yarn runs the command instantly

Steps to Reproduce

1. Have a large monorepo with 176packages in the workspace.
2. yarn install
3. Run any yarn run xxxx command in any of the packages folder.

Environment

• Node Version: 10.15.3
• Yarn v1 Version: 2.0.0-rc.29.git.20200218.926781b7
• OS and version: MacOS Catalina

[merceyz]

Closing as this was fixed in #998