Fix compatibility with TB >= 2.2

[cliffwoolley]

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https://github.com/tensorflow/tensorboard/pull/3539 in TensorBoard 2.2 dropped the legacy DB mode, so the unused optional db_* parameters to base_plugin.TBContext() should be dropped, as in https://github.com/tensorflow/tensorboard/commit/628b78fe3efbd98df84410a8841ff96fefa3beac#diff-9f7ffee070d3d2429db0b7178d355ec6L229-L241

[cliffwoolley]

/cc @wchargin

[leonardschneider]

Why is this not merged already? Bumped into this issue.

[cliffwoolley]

I've updated this PR from last year to also include TB 2.3 and TB 2.4 now.

Plus the newer, simplified implementation should allow better future-proofness as well: Instead of pulling out a huge chunks of the entry function to TensorBoard (which by the way no longer exists in TB 2.4) and reimplementing it mostly just to catch the returned object to add to our tensorboard_manager; instead we now just wrap the unmodified TB function from the outside and add to the tensorboard_manager that way. Also we no longer attempt to implement any special multiplexing functionality since TB handles all that on its own and the threading being handled in two places was causing bugs.

[rvernaeshv]

Thanks for this fix... It helps me a lot

[wexder]

@lspvic can we merge this?

[cliffwoolley]

This seems to be working with TB 2.5 as well, fwiw.

[billshitg]

just tried this with TB 2.7 and it worked very well. amazing! thanks for the fix. why has it not been merged already?

[videodanchik]

@lspvic Could you please merge this feature to master and bump up the library version?