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d97555427c
Branches: main, 10.04
Add an (undocumented) method for ssdebug, to allow debugging of only the
initial thread in a multi-threaded program.
ssdb/ssdb.m:
Make the debugger_state mutable thread-local, so that all threads but
the initial one can execute as if debugging is disabled.
Add `pause_debugging' and `resume_debugging' predicates that the user
must call around calls to `thread.spawn'. Mercury only supports
thread-local mutables which inherit their values from the parent
thread, so when the thread is created the debugger_state mutable must
be set to `off'. The predicates may have other uses, too.
README.ssdebug:
List debugging of multi-threaded programs as a limitation.
96 lines
3.9 KiB
Plaintext
96 lines
3.9 KiB
Plaintext
-----------------------------------------------------------------------------
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SOURCE-TO-SOURCE DEBUGGER
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The source-to-source debugger (ssdebug, ssdb) operates by performing a
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high-level transformation of Mercury source code to provide a rudimentary
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debugger interface. As such, it has numerous limitations (see below), but
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can potentially work with all backends. It is mainly intended for when you
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cannot use the Mercury debugger `mdb', such as with the Java or high-level C
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backends.
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ssdebug is still an experimental feature.
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-----------------------------------------------------------------------------
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THE .ssdebug GRADE COMPONENT
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Compile your program in a grade with the ".ssdebug" grade component,
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e.g. java.ssdebug or hlc.gc.ssdebug.
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You may run the program as usual. To bring up the debugger prompt, set
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the environment variable SSDB beforehand.
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% SSDB=1 ./calculator
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1: 1 1 CALL calculator.main
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ssdb>
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As in mdb, the three numbers are the event number, call sequence number (CSN)
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and the stack depth. Type "help" to show a list of commands. All commands act
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like their mdb counterparts (with reduced functionality), except for `list'
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which prints the source code at the call site, not of the called procedure.
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The debugger will execute commands from `$HOME/.ssdbrc' and `.ssdbrc' in
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the current working directory, in order, at startup. You can put your
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aliases and settings in those files. Lines starting with the # character
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will be ignored.
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For Java grades, JDK 7 improves performance considerably.
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Early access releases are available from
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<http://java.sun.com/javase/downloads/ea.jsp>
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Programs built in .ssdebug grades use much more stack space (tail call
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optimisation is destroyed by the transformation). You will likely need to
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increase the stack size, e.g.
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JAVA='java -Xss10m' SSDB=1 ./calculator
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-----------------------------------------------------------------------------
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LIMITATIONS
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- There are no internal events. The only events are CALL, EXIT, REDO, FAIL,
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and, for Java grades, EXCP.
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- Standard library procedures are treated specially. Events will only be
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generated at the boundaries at which a user procedure calls and returns
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from a standard library procedure. No events will be generated when a
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standard library procedure calls another standard library procedure.
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- The "retry" command works by executing forwards until reaching the end of
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the call to retry, then recursively calling that procedure. Any side
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effects of continuing execution will be visible. If it is not possible to
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reach the end of the procedure to retry, the program will simply keep
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executing. Press ^C to get back the debugger prompt.
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- Exceptions are only handled in Java grades. Only a single EXCP event is
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generated when an exception is thrown, instead of propagating EXCP events
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up the call stack to the nearest exception handler.
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- In non-Java grades, the debugger's internal state will be inconsistent with
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the program's execution after an exception, so you had better quit the
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program and restart.
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- Breakpoints currently match procedures by module and name only. Predicates
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or functions with the same name but different arities will still match.
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The debugger will not warn you if you set a breakpoint on a non-existent
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procedure.
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- We provide the filename and line number of call sites, but not the location
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of the source code for the called procedure itself. Use mtags.
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- The print goal command does not distinguish predicates and functions.
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- Procedures with arguments which are neither `in' nor `out' will not be
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transformed, hence will not generate events when called.
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- Many commands available in mdb are not yet implemented for ssdebug.
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- There is no tab completion.
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- There is no I/O tabling.
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- Debugging of multi-threaded programs is not supported.
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-----------------------------------------------------------------------------
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