dart:isolate spawnUri should have a customizable package root

[nex3]

Right now, when starting an isolate with spawnUri, the package root is set to the same thing as the parent isolate's package root. This should be customizable; otherwise it's nearly impossible to run code with different dependencies than the host process in an isolate.

[floitschG]

package_isolate_test is affected by this, too.

[nex3]

Marked this as blocking #17156.

[lrhn]

We will need this feature.

It's impossible to do this fully dynamically in dart2js code, since package root is a compile time concept. Does dart2js have a strategy for supporting it?
Should the other main library be compiled separately, and should there be a check that the dynamic package root matches the one passed at compile time, and if it doesn't, the code won't work (just as if the main library URI doesn't match a compiled JS file).

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cc @a-siva.
cc @floitschG.

[munificent]

It's impossible to do this fully dynamically in dart2js code, since package root is a compile time concept. Does dart2js have a strategy for supporting it?

For the record, our use case with pub doesn't require it to work in dart2js so not supporting it on dart2js doesn't block us.

[floitschG]

I think that the other main library should be compiled separately.
Not sure about package-root check.

[nex3]

Marked this as blocking #20859.

[munificent]

Adding a milestone since Ivan agreed this would be done by end of 9/12. If I have that wrong, let me know.

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Added this to the 1.7 milestone.
Removed Priority-Unassigned label.
Added Priority-High label.

[lrhn]

cc @Skabet.

[andersjohnsen]

The CL is already available here: https://codereview.chromium.org/545483002

Please provide us with feedback as soon as possible (landing this will take a few more days, as we need to coordinate with Dartium efforts).

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Set owner to @Skabet.
Added Started label.

[nex3]

I've patched it in locally and it seems to work fine. It provided a 420ms improvement in one of my test cases, which is great.

[munificent]

It provided a 420ms improvement in one of my test cases, which is great.

\o/ \o/ \o/

[DartBot]

This comment was originally written by @zoechi

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When I launch several isolates they can't have different current working directories (in addition to different package roots)? As far as I know this is bound to the process.

When I launch an isolate from code that accesses files using relative paths this doesn't work without setting CWD first, but when I launch more than one isolate with different CWD requirements concurrently these will collide.

I went back from isolates to processes because of this in some use cases.
You might run into this as well - or maybe you have an idea how to solve this with isolates.

[andersjohnsen]

We are aware of the limitation in regard to CWD and isolates. Can you file a seperate bug for this, so we can track the progress? It's an area we have yet to fully investigate.

[DartBot]

This comment was originally written by @zoechi

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Done dartbug.com/20903

[andersjohnsen]

Landed the VM (and dummy Dartium) change today. Reassigning to Dartium.

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Removed the owner.
Removed this from the 1.7 milestone.
Removed Area-Library, Library-Isolate labels.
Added Area-Dartium, Triaged labels.

[munificent]

\o/

[nex3]

Unmarked this as blocking #20859.

[kasperl]

Added this to the 1.9 milestone.

[kevmoo]

Is this fixed?

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Set owner to @sgjesse.