Support WeChat mini app environment

[pyu10055]

To compensate the differences between browser and WeChat mini app:

• WeChat mini app runs on JS core (ios) which does not have document, window, and setImmediate function or objects.
• When creating a GPGUContext with a existing context, it needs to store the context for the GL version, otherwise it would be picked later.
• expose setTensorTracker function to allow external backend registration to use.

This PR also fix the inconsistency issue with GPGPUContext constructor, it should always cache the rendering context.

---

This change is 

[nsthorat]

I don't think we need most of this code. You can already register a custom backend:

tf.ENV.registerBackend('wechat', () => new WeChatBackend());

We could expose registerBackend on the top-level tf.

As for the custom WebGL Context, the WeChatBackend should extend the WebGLBackend. The constructor allows passing a GPGPUContext:
https://github.com/tensorflow/tfjs-core/blob/master/src/kernels/backend_webgl.ts#L563

The GPGPUContext allows passing a WebGL Context.

So I think we have all the public facing API we need to do this.

Am I missing something?

Reviewed 1 of 7 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov and @pyu10055)

---

yarn.lock, line 8 at r1 (raw file):

  version "0.0.38"
  resolved "https://registry.yarnpkg.com/@types/estree/-/estree-0.0.38.tgz#c1be40aa933723c608820a99a373a16d215a1ca2"
  integrity sha512-F/v7t1LwS4vnXuPooJQGBRKRGIoxWUTmA4VHfqjOccFsNDThD5bfUNpITive6s352O7o384wcpEaDV8rHCehDA==

please revert this file, you have an old yarn (you should update it! this has happened a couple times :) )

---

src/browser_util.ts, line 18 at r1 (raw file):

 */

const delayCallback: Function = typeof requestAnimationFrame !== 'undefined' ?

this is getting pretty hard to parse now, how about:

const delayCallback: Function;
  if (...) {
    delayCallback = ...
  } else if (...) {
  }
}

[dsmilkov]

Reviewed 1 of 7 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov and @pyu10055)

---

src/environment.ts, line 466 at r1 (raw file):

}

export function getGlobalNamespace(): {ENV: Environment} {

why do you need to export this method?

---

src/index.ts, line 47 at r1 (raw file):

export {RMSPropOptimizer} from './optimizers/rmsprop_optimizer';
export {SGDOptimizer} from './optimizers/sgd_optimizer';
export {Scalar, setTensorTracker, Tensor, Tensor1D, Tensor2D, Tensor3D, Tensor4D, TensorBuffer, variable, Variable} from './tensor';

you shouldn't expose this. just make a new custom backend and set it.

---

src/kernels/webgl/gpgpu_context.ts, line 54 at r1 (raw file):

    if (gl != null) {
      this.gl = gl;
      setWebGLContext(glVersion, gl);

instead of calling it here, expose this method as tf.webgl.setWebGLContext() and call it from the wechat repo. Also make a custom WeChat backend that extends from the WebGL backend.

[pyu10055]

I think there is an inconsistency in the GPGPUContext constructor, when the rendering gl context is not provided, an default context is created automatically, and cached in its local GL_VERSION => context map, but if a external gl context is provided the caching is not done, which causes issues later.
I think this is a bug, and the setWebglContext method should not be exposed to custom backend, since it is an internal implementation details that custom backend should not need to know.

Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov)

---

src/environment.ts, line 466 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

why do you need to export this method?

Currently other places also are doing the same logic to find the exposed symbol, for example fetch for ioHandler. By exposing this, we can centralize this search logic and potential caching the namespace.

---

src/index.ts, line 47 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

you shouldn't expose this. just make a new custom backend and set it.

Without exposing this, how can a custom backend access the internal variable trackFn in the tensor.ts file?

---

src/kernels/webgl/gpgpu_context.ts, line 54 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

instead of calling it here, expose this method as tf.webgl.setWebGLContext() and call it from the wechat repo. Also make a custom WeChat backend that extends from the WebGL backend.

as I stated in the response to Nikhil, this is an internal details of how webgl backend looks up context, custom backend should not need to worry about.

[pyu10055]

I know this can be done with an external backend, but I think it should be fixed instead of pushing out.

Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov)

[dsmilkov]

Hey can you point us to the WeChat repo. Would be good to see the code there and which flags you are overriding.

Reviewed 3 of 7 files at r1, 2 of 3 files at r2.
Reviewable status: 0 of 1 approvals obtained (waiting on @pyu10055)

---

src/environment.ts, line 466 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

Currently other places also are doing the same logic to find the exposed symbol, for example fetch for ioHandler. By exposing this, we can centralize this search logic and potential caching the namespace.

Since we are making this a public API, let's add this as a property global to the Environment class, so users can do tf.ENV.global to access it.

---

src/index.ts, line 47 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

Without exposing this, how can a custom backend access the internal variable trackFn in the tensor.ts file?

You won't need this after this PR is in: #1517 so remove the export.

---

src/kernels/webgl/gpgpu_context.ts, line 54 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

as I stated in the response to Nikhil, this is an internal details of how webgl backend looks up context, custom backend should not need to worry about.

sounds good. let's do it this way for now.

[pyu10055]

tf.ENV.set('WEBGL_VERSION', 1);
and for iOS:
tf.ENV.set('WEBGL_RENDER_FLOAT32_ENABLED', false);

Reviewable status: 0 of 1 approvals obtained

---

src/environment.ts, line 466 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

Since we are making this a public API, let's add this as a property global to the Environment class, so users can do tf.ENV.global to access it.

adding the global inside the Environment object would cause recursive reference, which might be issue for logging. I added a caching at the file level.

[dsmilkov]

Reviewable status: 0 of 1 approvals obtained (waiting on @pyu10055)

---

src/environment.ts, line 466 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

adding the global inside the Environment object would cause recursive reference, which might be issue for logging. I added a caching at the file level.

Sorry i wasn't clear. Add a getter to the Environment class and don't export getGlobalNamespace:

  get global() {
    return getGlobalNamespace();
  }

This way users can access tf.ENV.global which points them to window/process/global depending on the environment they are in.

[pyu10055]

Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov)

---

src/environment.ts, line 466 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

Sorry i wasn't clear. Add a getter to the Environment class and don't export getGlobalNamespace:

  get global() {
    return getGlobalNamespace();
  }

This way users can access tf.ENV.global which points them to window/process/global depending on the environment they are in.

Done.

[dsmilkov]

Reviewable status: 0 of 1 approvals obtained (waiting on @pyu10055)

---

src/environment.ts, line 466 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

Done.

Remove the _global variable since you don't really need it.

[pyu10055]

Reviewable status: 0 of 1 approvals obtained (waiting on @pyu10055)

src/environment.ts, line 466 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…
Remove the _global variable since you don't really need it.
This cache speeds up the lookup, since now this method can be called multiple times.

[dsmilkov]

Reviewable status: 0 of 1 approvals obtained

---

src/environment.ts, line 466 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

Remove the _global variable since you don't really need it.

LGTM