Don't initialize an SDK session if we are only going to be launching …

…the app (#1768)

rerun_py/rerun_sdk/rerun/__init__.py

@@ -306,18 +306,23 @@ def spawn(port: int = 9876, connect: bool = True) -> None:
         print("Rerun is disabled - spawn() call ignored")
         return
 
+    import os
     import subprocess
     import sys
     from time import sleep
 
+    # Let the spawned rerun process know it's just an app
+    new_env = os.environ.copy()
+    new_env["RERUN_APP_ONLY"] = "true"
+
     # sys.executable: the absolute path of the executable binary for the Python interpreter
     python_executable = sys.executable
     if python_executable is None:
         python_executable = "python3"
 
     # start_new_session=True ensures the spawned process does NOT die when
     # we hit ctrl-c in the terminal running the parent Python process.
-    subprocess.Popen([python_executable, "-m", "rerun", "--port", str(port)], start_new_session=True)
+    subprocess.Popen([python_executable, "-m", "rerun", "--port", str(port)], env=new_env, start_new_session=True)
 
     # TODO(emilk): figure out a way to postpone connecting until the rerun viewer is listening.
     # For example, wait until it prints "Hosting a SDK server over TCP at …"

rerun_py/src/python_bridge.rs

@@ -107,17 +107,28 @@ fn rerun_bindings(py: Python<'_>, m: &PyModule) -> PyResult<()> {
     // called more than once.
     re_log::setup_native_logging();
 
+    // We always want main to be available
+    m.add_function(wrap_pyfunction!(main, m)?)?;
+
+    // These two components are necessary for imports to work
+    // TODO(jleibs): Refactor import logic so all we need is main
+    m.add_function(wrap_pyfunction!(get_registered_component_names, m)?)?;
+    m.add_class::<TensorDataMeaning>()?;
+
+    // If this is a special RERUN_APP_ONLY context (launched via .spawn), we
+    // can bypass everything else, which keeps us from preparing an SDK session
+    // that never gets used.
+    if matches!(std::env::var("RERUN_APP_ONLY").as_deref(), Ok("true")) {
+        return Ok(());
+    }
+
     python_session().set_python_version(python_version(py));
 
     // NOTE: We do this here because we want child processes to share the same recording-id,
     // whether the user has called `init` or not.
     // See `default_recording_id` for extra information.
     python_session().set_recording_id(default_recording_id(py));
 
-    m.add_function(wrap_pyfunction!(main, m)?)?;
-
-    m.add_function(wrap_pyfunction!(get_registered_component_names, m)?)?;
-
     m.add_function(wrap_pyfunction!(get_recording_id, m)?)?;
     m.add_function(wrap_pyfunction!(set_recording_id, m)?)?;
 
@@ -150,8 +161,6 @@ fn rerun_bindings(py: Python<'_>, m: &PyModule) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(log_cleared, m)?)?;
     m.add_function(wrap_pyfunction!(log_arrow_msg, m)?)?;
 
-    m.add_class::<TensorDataMeaning>()?;
-
     Ok(())
 }