Speed up debugger connection

[andreidanila1]

Existent problem

Connecting to a device-heavy IIO context (e.g. M2k, ADRV9009) caused the IIOExplorer UI to freeze for several seconds before becoming responsive. Profiling identified two root causes:

Stylesheet propagation over hundreds of already-constructed widgets

Style::setBackground is called in IIOExplorer::setupUI, after IIOModel has already been constructed with all its IIOWidget children attached to m_mainWidget. Setting a stylesheet on a parent widget triggers Qt to recursively re-polish every child widget in the hierarchy. With hundreds of IIOWidgets already attached, this single call accounted for 64.7% of the total freeze.

Blocking IIOWidget construction on the UI thread

IIOModel::IIOModel built all IIOWidget instances for every device and channel attribute at connection time. Internally, IIOWidgetBuilder::createUIS() performs synchronous libiio reads for every attribute that exposes an _available variant:

res = iio_channel_attr_read(m_channel, m_optionsAttribute, buffer, ATTR_BUFFER_SIZE);                                                              
res = iio_device_attr_read(m_device,  m_optionsAttribute, buffer, ATTR_BUFFER_SIZE); 

These reads are blocking network calls (USB/IP backend) made on the UI thread, one per attribute, before the window even appears. On a device with 20 channels × 5 _available attributes this results in 100 sequential blocking reads. Beyond the libiio reads, IIOWidgets construction itself is expensive (especially for device-heavy contexts) - each widget goes through style application, layout setup (and others) at creation time.

Changes

• Postpone IIOWidget construction to first expand/select
  • Building IIOWidgets for every device and channel attribute at connection time caused multi-second UI freezes on device-heavy contexts (e.g. M2k, ADRV9009).
• Background population of all device/channel nodes
  • Populate the IIOTree nodes in different QEvents to prevent the application from freezing. I also retain the previous commit's functionality, allowing a node to be loaded on demand by selecting or expanding it.
• IIOExplorer API updates

Tested on

I've tested this on Ubuntu 22.10, Kuiper 2-64, and Windows ADI using the ADRV9009 multidevice emu.
If possible, please also test on arm32 (and arm64) as well as macOS.
On Ubuntu, the performance improved from 4 seconds to 100 ms, and on Kuiper from ~50 seconds to ~2 seconds.

[Andrei-Fabian-Pop]

Looks nice, Godspeed 🫶

[bindea-cristian]

Super fast loading

[IonutMuthi]

I tested both using ssh and remote connection via IP on ADRV9375

Using ssh works fast.

Using the IP throw Analog VPN is slow, but this is generally true when using the VPN to access devices in the network