13. Inspecting and Debugging in GemStone

Figure 13.1   GS Basic Tab

When inspecting a GemStone server object, the inspector provides additional tabs with the GS prefix, indicating that these apply to a GemStone server object.

In addition, there is a tab labeled “GS Delegate”, which allows you to examine the internal state of the object’s delegate in GemBuilder.

Figure 13.2   GS Delegate Tab

When inspecting a client object that has a corresponding GemStone server object (or vice versa), the inspector allows you to view both the client object and the server object in the same inspector. Client objects with corresponding server objects includes replicates of server objects, forwarders to server objects, stubs, and objects that are always mapped such as nil, true, false, SmallIntegers, and Characters. When you are inspecting one of these objects, you will see two sets of tabs: one that allows you to examine the client object, and a second similar set of tabs with the GS prefix, to examine the associated GemStone server object.

For example, if you select the following text and Inspect it:

GBSM evaluate: 'Array with: ''aaa'' with: ''bbb'' with: 23'

The following inspector displays both the client and server object:

Figure 13.3   Inspector for Objects that exist on both client and server

Executing code in the inspector

In the evaluation pane of the inspector, or any other pane, the use of “self” is resolved according to the following rules:

• Do it, Print it, Inspect it and Debug it resolve self to the client object.
• GS-Do it, GS-Print it, GS-Inspect it, and GS-Debug it resolve self to the GemStone server object.
• When the GS Delegate tab is selected, Do it, Print it, Inspect it and Debug it resolve self to the delegate object, as shown in Figure 13.4.

Figure 13.4   Inspector Evaluation Pane.

---

Figure 13.5   Debugger

When GemStone Smalltalk execution is interrupted, it either directly opens the Debugger, or a notifier that includes a Debug button. Selecting the Debug button opens the Debugger. A runtime error opens a notifier, while a breakpoint, user interrupt, or an Object >> pause opens a debugger. You may also use the menu item GS Debug-it to open a Debugger on a code snippet, which opens a debugger on that code.

The Debugger’s stack pane displays the active call stack and allows you to choose a context (stack frame) from that stack for manipulation in the window’s other panes. Both GemStone server and client contacts are listed. GemStone server contexts begin with “GS”.

The Debugger is much like the client Smalltalk debugger, with the menus enhanced with GemStone options. Like other GemBuilder text areas, the debugger source code pane provides commands to execute GemStone Smalltalk.

Colored contexts

You may configure VisualWorks to color the GemStone server contexts, to distinguish them from client contexts. To do this, select the Settings button on the Launcher toolbar, or go to System > Settings, and select Debugger (under Tools). Select the button to edit the Context List Presentation. If no Patterns exist, create a new Pattern for Everything with the Pattern String *. Then, create a new Pattern with the Pattern String $L$GS*, and select a color for the GemStone server contexts text. This new Pattern must be above the Pattern String *.

The following example demonstrates doing the same action using a script.

| patterns contextPattern|

patterns := OrderedCollection new. 

contextPattern := (ClientContextPatternSpec new)

	color: (ColorValue red: 0.2 green: 0.0 blue: 0.5);

	name: 'GemStone';

	pattern: '*$L$GS*';

	yourself.

patterns add: contextPattern.

contextPattern := (ClientContextPatternSpec new) 

	color: ColorValue black;

	name: 'Everything';

	pattern: '*';

	yourself.

patterns add: contextPattern.

ContextListPolicyEditor.Patterns := patterns.

Disabling the Debugger

In some cases, you may want to disable the GBS debugger. You can disable and enable the debugger using the following expressions:

GBSM enableGbsDebugger

GBSM disableGbsDebugger

Disabling the GBS debugger restores the base VisualWorks debugger.

Step Points

For the purpose of determining exactly where a step will go during debugging, a GemStone Smalltalk method is composed of step points. You can set breakpoints at any step point.

Generally, step points correspond to the message selector and, within the method, message-sends, assignments, and returns of nonatomic objects. However, compiler optimizations may occasionally result in a different, nonintuitive step point, particularly in a loop.

More detail on step points within GemStone Smalltalk methods is provided in the Topaz Programming Environment, Chapter 2.

Example 13.2 indicates step points with numbered carets, as is output in the topaz environment.

includesValue: value

^1

"Return true if the receiver contains an object of the same value

as the argument. Return false otherwise."

| found index size|

found := false.

	^2

index := 0.

	^3

size := self size.

^5 	     ^4

[ found not & (index < size)] whileTrue: [

^6  ^8       ^7       ^9

	index := index + 1.

^11      ^10

	found := value = (self at: index)

		^14      ^13     ^12

	].

^found

^15

Breakpoints

You can set a breakpoint in any method by selecting the position in the source text and menu item Set Breakpoint. The step point nearest your cursor position is used for the breakpoint, and the first letter of the text following the breakpoint will be highlighted (colored and underscored).

You can remove the breakpoint by selecting the specific break and using the menu item Remove Breakpoint, or by using Remove All Breakpoints. Breakpoints can also be removed using the Breakpoint Browser, described in the next section. This tool also allows you to disable breakpoints, but leave them in your methods.

When the GemStone Smalltalk virtual machine encounters an enabled breakpoint during execution, GemStone opens the GemStone Debugger. In the Debugger you can interactively explore the context in which execution halted.

Breakpoint Browser

To see a complete list of the breakpoints you have set anywhere in your GemStone server code, use the Breakpoint Browser. You can open a Break point Browser using the Browse > Breakpoints menu item on the GemStone Launcher.

In addition to allowing you to examine, remove and add breakpoints, the Breakpoint Browser allows you to disable breakpoints without removing them, and later re-enable these breakpoints. These operations can be performed on a single selected breakpoint or on all breakpoints.

A breakpoint browser has two panes: the list of break points on top, and the source code associated with the selected breakpoint on the bottom.

Figure 13.6   Breakpoint Browser

---