fix: Safe Execute on JVM

[bitsandfoxes]

Basically a followup on the scope sync changes in #2107
Fixes #2164

Problem

The issue originates from the following scenario:

1. User/plugin code runs on a background thread
2. That thread attaches to the JVM to do some work
3. It triggers a scope sync
4. We end up in the SDK, on the same thread
5. Since it's not on the main thread it attaches/detaches for the scope sync with the Android SDK
6. The thread executing user/plugin code was detached prematurely, causing a crash with attempting to detach while still running code

The fix

Since we cannot verify whether the current thread is already attached or not we "have" to do the scope sync on a thread we actually control, so we can safely attach/detach. We only have to do that when not running on the main thread and we only do that on fire&forget scope sync calls. The rest of SentryJava is currently guaranteed - and now required - to run on the main thread.

Alternative attempts

I could not find a way to check whether the current thread is already attached to the JVM that works for all supported versions of Unity.

Check GetVersion

In versions 2022_and_newer it's possible to call AndroidJNI.GetVersion() which returns

• When not attached: 0
• When attached: the actual version

On older versions of Unity GetVersion always returns the actual version, creating a false positive.

Try-Catch AndroidException

I tried an approach by accessing AndroidObjects while not attached to capture the resulting AndroidException which again, worked on 2022_and_newer but straight up crashes the game on older versions.

[bitsandfoxes]

This is called by the SDK as part of the initialization process which is currently explicitly required to run on the main thread. I'm adding the check here now too so any future changes to the initialization flow (i.e. programmatic through user code) is not turning into a footgun.

[bitsandfoxes]

Same as above.

[bitsandfoxes]

Same as above.

[bitsandfoxes]

Same as above.

[bitsandfoxes]

Same as above.

[vaind]

LGTM & nice writeup. 🤞 this really fixes the issue.

[bruno-garcia]

CI flaked because GitHub got unicorns

Invoke-WebRequest: /home/runner/work/sentry-unity/sentry-unity/scripts/download-sentry-cli.ps1:23
Line |
  23 |      Invoke-WebRequest -Uri "$baseUrl$name" -OutFile $targetFile
     |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     |           Unicorn! · GitHub            body {        
     | background-color: #f1f1f1;         margin: 0;         font-family:
     | "Helvetica Neue", Helvetica, Arial, sans-serif;       }       
     | .container { margin: 50px auto 40px auto; width: 600px; text-align:
     | center; }        a { color: #4183c4; text-decoration: none; }      
     | a:hover { text-decoration: underline; }        h1 { letter-spacing:
     | -1px; line-height: 60px; font-size: 60px; font-weight: 100; margin: 0px;
     | text-shadow: 0 1px 0 #fff; }       p { color: rgba(0, 0, 0, 0.5);
     | margin: 10px 0 10px; font-size: 18px; font-weight: 200; line-height:
     | 1.6em;}        ul { list-style: none; margin: 25px 0; padding: 0; }  
     | li { display: table-cell; font-weight: bold; width: 1%; }        .logo
     | { display: inline-block; margin-top: 35px; }       .logo-img-2x {
     | display: none; }       @media       only screen and
     | (-webkit-min-device-pixel-ratio: 2),       only screen and (  
     | min--moz-device-pixel-ratio: 2),       only screen and (    
     | -o-min-device-pixel-ratio: 2/1),       only screen and (       
     | min-device-pixel-ratio: 2),       only screen and (               
     | min-resolution: 192dpi),       only screen and (               
     | min-resolution: 2dppx) {         .logo-img-1x { display: none; }      
     | .logo-img-2x { display: inline-block; }       }        #suggestions {
     | margin-top: 35px;         color: #ccc;       }       #suggestions a {
     | color: #666666;         font-weight: 200;         font-size: [14](https://github.com/getsentry/sentry-unity/actions/runs/15878142374/job/44770897275?pr=2215#step:11:15)px;   
     | margin: 0 10px;       }                                       
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