Platform.environment seems like a copy of env variables, created for every get of the getter

[sethladd]

Not sure what the right behavior/docs are, but I found it surprising that Platform.environment returns a new Map every time I access the getter.

import 'dart:io';

void main() {
  var stuff = Platform.environment;

  print(stuff);

  stuff['foo'] = 'bar';

  print(stuff);

  var stuff2 = Platform.environment;

  print(stuff2);

  print(stuff2['foo']); // XXX this is null
}

Either Platform.environment is meant to return a singleton map (one map for the platform), or is meant to return an unmodifiable map, or is meant to always return a mutable copy.

If the last case, I recommend we update the API docs.

Thoughts?

[sgjesse]

What the title says is exactly what is happening.

The reason for creating a new map each time is that the process environment might change. However we do not have any way of changing the environment from Dart, but it could still occur from e.g. a native extension.

I basically see three options:

Change the result of Platform.environment to an unmodifiable map and document that. We could even make it a singleton, as the environment cannot be changed from Dart. This does not capture the case of the environment being modified from a native extension, but as mentioned below this could be dangerous.

Implement a map which works directly with the process environment. That is the full fledged solution where operator[] uses getenv, operator=[] uses setenv, remove calls

Deprecate Platform.environment and add Platform.getenv, Platform.setenv, ... mapping more directly to the underlying C functions. This gets rid of accessing the environ global (calling _NSGetEnviron() on Mac OS) which can be dangerous if native extensions modify the environment.

The reason for also suggesting 3 is that in general there is a threading issue with reading the full environment on Linus/Mac OS. The environment is in a global variable, and reading it while another thread is modifying is not safe. This issue is not present on Windows where a copy of the environment is provided.

I think solution 1 should be fine. I don't see much need for modifying the environment except when starting a new process which is possible when starting a new process.

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Set owner to @sgjesse.
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[sethladd]

Option 1 sounds good to me for now. Thanks for taking a look!

[sgjesse]

Fixed in https://code.google.com/p/dart/source/detail?r=31468.

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[kevmoo]

Removed Area-IO label.
Added Library-IO label.