Jinsight Reference Manual

Method Histogram View

Purpose · Elements · Interpretation · Related Views

Execution Pattern View

Initial Overview:

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Purpose

Elements

Main View

An object is represented by a vertical stripe that is colored according to the object's class.  Time progresses downward in the view, and time units appear at the right side of the view.  A stripe's top edge coincides with the time of a particular method call; the stripe's height reflects the total time spent executing the corresponding method.  When the user zooms the view in to a sufficient level of detail, a labeled horizontal line leads to the stripe's top left corner and identifies the method call, its argument types, and its return type.  The line and label appear in red if the method is a constructor, black otherwise.

The left end of the line is attached to the calling object's stripe. The line's vertical position along the caller's stripe suggests when the call occurred (e.g., early or late) in the calling method. A stripe's furthest extent down the view indicates the time of the method's return.

Stripes cascade to the right as one method sends a message to an object, whose responding method in turn sends a message to another object, and so on. Stripes are grouped in columns by thread, a thin black vertical line separating one column from another.  The name of each thread appears at the top of its column in a fixed gray header area.. 

By default, the leftmost column is reserved for garbage collection information. (Although depicted as a thread, the garbage collection "thread" does not behave as a thread in several other aspects -- for example, it is not selectable as a thread). A thin rectangle appears in this column whenever an object is garbage collected.   As with other objects and methods in the view, you left-click on the collected object to select it.  Large raised gray rectangles represent garbage collection phases in the trace.

See also Using Slices in the Execution View for a detailed discussion of how this view may be used with slices and workspaces.

Selection

You may select methods, objects, threads, or individual method invocations from the execution view in various ways:

• Left-clicking on a stripe selects the corresponding object; left-clicking on a method name (or on whitespace below it) selects the corresponding method.  Zooming out far enough will only show the stripes, in which case left-clicking on it will select the corresponding method.
• You may select one or more individual method invocations, or one or more threads, using the popup menu obtained by right-clicking in the view.
• You may select a region of activity by dragging the mouse over a rectangular area in the view, while holding down the left mouse button and the Shift key. This will select the highest-level method invocations that start and end within the selected area.

The Execution view will reflect the currently selected elements (whether they were selected in this view or another) by highlighting them in yellow. Selected objects, methods, or invocations will appear as a yellow highlight on the appropriate elements, and everything to the right of them in that thread. Selected threads will appear with highlighted headings.

Menus

• Popup menus. Right-clicking on empty space in a thread produces a popup menu which lets you Hide This Thread (remove it from the view), Show This Thread Only (remove all other threads from the view), or Select This Thread (deselecting any others already selected). If a thread is already selected, this popup activates another choice, to Add This Thread to Current Selection.

Right-clicking on a stripe (object) or on a method name (or the whitespace below the line) produces a different popup menu. For cases of repetitive method calls from an object, Detect Repetition will visually consolidate the repetitive calls, and Remove Repetition will undo that visual consolidation. Select This Invocation will select this particular method invocation, deselecting other selections. If there are already method invocations selected, Add This Invocation to Current Selection will append this selection to the other method invocations selected.

The remaining popup menu options are active only when current selections exist. Drill Down from Selected Items lets you open a view that is restricted to the current selections. Create a New Slice will create one or more new slices from the current selections. You can create either a single slice From Selected Items or one slice For Each Selected Item. Choosing Limit an Existing Slice presents the set of execution slices you can choose to limit to Selected Items.
 

• Options menu. Two of the options are on by default. Short Names shortens the length of character data displayed in the status line and on the method name lines in the view; package names and method argument information are omitted. The second default option, Stretch while Zooming, causes the time dimension to be expanded or contracted to fit the zoom area exactly to the window.  When this option is not selected, the zoom rectangle is constrained so that it matches the aspect ratio of the window.

  Normally, it's impossible to tell that an object has been garbage collected by inspecting stripes in a user thread.  The only evidence of collection is a single rectangle in the GC thread column, probably well downstream of most method calls on the object.  When chosen, Draw Collected Objects Empty causes the stripes of every collected object to appear in outline form, making the objects easy to identify as having been collected.

  Detect All Repetitions changes the Execution View so that repetitive call sequences on the execution stack are summarized visually. A gray box summarizes the repetitions and replaces the individual call sequences, which instead appear as smaller gray boxes on the left, unless they are too numerous.  A darker gray box on the right expands the first repetition in detail, and contains a repetition count at the bottom left.  Further detail beyond this execution level is suppressed.  Option Remove All Repetitions reverts to showing all call sequences individually.

  Color by Slice colors the stripe, the horizontal line, and method name label based on the slice that the method invocation falls into. See Using Slices with the Execution View for more details.

  A final option, Font Scaling, will make text grow and shrink just like other elements of the view when it's zoomed.  Text remains a constant size by default.
   

• Zoom menu. These options help you to navigate around the Execution View, by zooming and by varying the time dimension in the view. Home works slightly differently in this view than in others:  it scales and zooms the view so that the entire execution is visible.  That means the view will be zoomed so that all threads to be viewed fit snugly horizontally, and time will be scaled if necessary to make the entire execution fit vertically.

Zooming can be done in several ways. One is to drag the mouse over a rectangular area to zoom in on. Another is to use the plus and minus keys to zoom in and out. Additional menu options remember previous zoom positions you have traversed, and allow you to return to them. Toggle Zoom alternates between the two most recent zoom positions viewed. If you use Mark Zoom to save the current zoom position, then you can go to it later using the option Zoom To Mark. Also, a partial history of zoom positions is kept, using the most recent branch taken. Thus you can move back and forth along this zoom path history, with Zoom Back and Zoom Forward.

Zooming changes both the vertical (time) dimension and the horizontal dimension, whereas Expand Time and Compress Time rescale only the (time) dimension of the view.
 

• Selected menu. These options are active only when current selection(s) exist. Drill Down from Selected Items lets you open a view that is restricted to the current selections. Create a New Slice will create one or more new slices from the current selections. You can create either a single slice From Selected Items or one slice For Each Selected Item. Choosing Limit an Existing Slice presents the set of execution slices you can choose to limit to Selected Items.

 
• Help menu. Selecting Help in a view attempts to use your browser to display the Reference Manual documentation for that view. The browser program location is specified in the environment variable JINSIGHT_BROWSER, in the shell script named jinsight that invokes the visualizer.

 
• Threads menu. The Threads menu lets you control which threads appear in the view and their left-to-right ordering.  The menu has at least four entries.  Show All Threads makes all threads visible, including the garbage collection thread. You may also Hide All Threads or Show Selected Threads Only.. Sort Threads Now sorts columns by thread name, left to right.  It affects all columns except GC, the garbage collection thread.  The GC thread appears leftmost unless it is hidden explicitly with the GC menu entry, which toggles that thread.

The Threads menu has additional entries, one per user thread.  You can toggle each thread entry independently, to be viewed or hidden.  If you want to view just a few threads out of many, use Hide All Threads to clear the view, then toggle the threads of interest.

Bottom Panel

As you zoom out, details will disappear progressively.  Method names disappear first, followed by the lines they label.  At that point, wider, nearly abutting vertical stripes replace the object stripes and their calling methods.  Selecting one of these stripes is equivalent to selecting the corresponding calling method.

Positioning the cursor over a stripe or to its immediate left displays the following information in the status line: thread name, class and method names, instance identifier, time of call (instantiation time in the case of constructors), and the cumulative time spent in the method. Positioning the cursor over a rectangle in the GC column identifies the garbage-collected object.  Positioning the cursor elsewhere in the view displays only the thread name and time corresponding to the pointer's vertical position.

Interpretation

Program Understanding

The Execution view gives you a bird's-eye view of the entire execution.  When fully zoomed out, it shows at a glance which threads are active and when, how much garbage collection is going on, and hotbeds of activity.  Then you can zoom in on interesting areas to view their details. It's easy to note repetitive behavior such as iteration and recursion, which manifest themselves as repeated patterns in the horizontal and vertical dimensions. Different phases of the execution—such as initialization, quiescent periods, computation, and shut-down—are often discernible, giving you a feel for their relative importance, complexity, and cost.

Debugging

The view is good for investigating the causes of infinite loops and recursion, deadlocks, and unexpected call patterns in general.  The absence of garbage collection will be obvious, although its causes may not be.

Tuning

Excessive looping, recursion, and object creation; redundant calls; long-lived or oft-called methods—all are examples of tuning opportunities that are often evident in this view. It can also help you load-balance your system by shifting responsibilities among threads.

Related Views

Selecting an object or method in this view and then consulting one of the Histogram views lets you compare the object or method to others of its class and explore dependencies among them.

Method Histogram View

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