The System Monitor is a system for displaying the vital signs of a Fuchsia device and its processes. Samples are collected for global and per-process CPU, memory usage, and process list which are relayed to the Host computer for display.
A filtered sample is a representation of actual samples. E.g. a filtered sample might have the value 900 if filter was averaging actual samples of 700, 800, 1000, and 1100. Note that the filtered sample doesn't match any of the actual samples in this example.
A mathematically generated summary of 0 to many (physical) Samples. E.g. if we render 3 columns on the screen for 12 actual Samples, each Logical Sample Value will be computed from 4 actual Samples. If no scaling is done by GUI, then each Logical Sample will naturally align with one column of the rendered graph.
A graph rendering filter. Scales the graph output so that the high and low values are framed nicely on the screen. The data is scaled dynamically.
A message sent from the GUI to the dockyard. It specifies the time range, sample streams, and filtering desired.
A message sent from the dockyard to the GUI to answer a Sample Stream Request. It includes the filtered sample data (a Sample Set) for each of the requested sample streams.
The physical Samples that taken together make up a Logical Sample.
A portion of a |Sample Stream|. E.g. a Sample Stream might have 100,000 Samples and a Sample Set might only show filtered view of a 1,200 of them.
The logical, named idea of where Samples come from. E.g. “cpu”, “memory”, “process” are Sample Categories.
An ordered set of Samples for a given Sample Category. E.g. all the Samples for “cpu0”.
A number used to uniquely refer to a Sample Stream or other named entity. The Dockyard ID is 1:1 with a specific Dockyard Path.
A UTF-8, case sensitive text string referring to a Sample Stream or other named entity. The path value is primarily used in the GUI (for humans), internally the Dockyard ID is used. E.g. “cpu:0”, “physMem”, “procCount” are Dockyard Paths.
A graph rendering filter. Blends neighboring samples to create a graph with less noise.
The main components of the System Monitor execute as separate processes (either on the Host computer or the Fuchsia device).
There are several components of the System Monitor
At the highest level, the GUI displays samples collected from the Fuchsia device (in graphs or charts as appropriate), which come from the Dockyard on the Host. The GUI for the System Monitor is not included in this source directory. It is implemented at a higher level (or petal).
The Dockyard is used as a library (with no GUI itself) that collects data from the Fuchsia device through the transport system. It responds to requests from the GUI for digestible (i.e. small) sections of data that will be presented to the user.
The Harvester runs on the Fuchsia device, acquiring Samples (units of introspection data) that it sends to the Host using the Transport system. The Harvester does not store samples.
The communication between the Harvester and the Dockyard is handled by the Transport which will run on both the Host machine and the Fuchsia device.