MT Icon Instrumentation

• MT Icon includes instrumentation of the run-time system to provide events for activities that take place during program execution
  
• a monitoring program (MP) loads a source program (SP) to be monitored
  
• in the terminology of the monitoring model described earlier, SP is the event source (ES) and MP is the report processor (RP)
  
• MP requests an event, which turns control over to SP
  
• SP runs until an event occurs, at which point control is returned to MP to process the event
  
• SP is not "aware" it is being monitored
  
• MP controls event reporting and can specify only those kinds of events it wants
  
• the flow of control looks like this:
  
  

Events

• there are many kinds of events (about 150) that can occur in the run-time system
  
• an event consists of two parts: a code and a value
  
• the code identifies the kind of the event, such as set membership test
  
• the value provides some identifying information about the specific event; for example, in the case of set membership test, it is the set itself
  
• the code is a one-character string
  
• the main categories of events are

expression evaluation
structure access
string scanning
type conversion
storage allocation
garbage collection

• in programs, event codes are represented by symbolic constants; for example E_Smember is the symbolic name for set membership test

Monitoring Programs

• the structure of an MP is simple:

link evinit               # support procedures

$include "evdefs.icn"     # event definitions

procedure main(args)

   EvInit(args) | ...     # load the SP

   while EvGet() do {     # request event in SP
       ...                # process event
      }

       ...                # final processing (if any)


end

• the library module evinit includes procedures that support monitoring activities
  
• the include file evdefs.icn (on LPATH) provides symbolic definitions for event codes
  
• args provides the command line arguments, including the program to load
  
• the command line to an MP named allocview might have the form

allocview rsg -l 1000 <rsg.dat

which specifies that allocview is to monitor rsg run as

rsg -l 1000 <rsg.dat

• EvInit(args) calls load() and initializes monitoring; it may fail
  
• the call of EvGet() requests an event
  
• when an event occurs, the procedure EvGet() returns and the event code and value are set in &eventcode and &eventvalue in the MP
  
• the MP takes actions depending on the values of these keywords
  
• note that in the case of an event such as set membership test, &eventvalue contains (a pointer to) the set in SP
  
• an argument to EvGet() can be used to specify the kinds of events that are wanted
  
• such arguments are called masks
  
• there are symbolic names for frequently used masks; for example, StructMask is the name of the mask for structure access events
  
• thus

EvGet(StructMask)

limits the kinds of events reported to those associated with structure access