This library provides utilities that are primarily intended for
interactive usage in a threaded Prolog environment. It allows for
inspecting threads, manage I/O of background threads (depending on the
environment) and manipulating the debug status of threads.
- threads
- List currently known threads with their status. For each thread it lists
the id, class, status, debug status, CPU
time and current stack usage. If a thread is listed with Debug
set to‘X’, it cannot be debugged. If the Debug is
show as‘V’, it is running in debug mode (see debug/0)
and responds to spy points and
break points.
- join_threads
- Join all terminated threads. For normal applications, dealing with
terminated threads must be part of the application logic, either
detaching the thread before termination or making sure it will be
joined. The predicate join_threads/0
is intended for interactive sessions to reclaim resources from threads
that died unexpectedly during development.
- [det]with_stopped_threads(:Goal,
Options)
- Stop all threads except the caller while running
once(Goal).
Note that this is in the thread user utilities as this is not something
that should be used by normal applications. Notably, this may
deadlock if the current thread requires input from some other
thread to complete Goal or one of the stopped threads has a
lock.
Options:
- stop_nodebug_threads(+Boolean)
- If
true (default false), also stop threads
created with the debug(false) option.
- except(+List)
- Do not stop threads from this list.
- bug
- Note that the threads are stopped when they process signals. As signal
handling may be delayed, this implies they need not be stopped before Goal
starts.
- [semidet]thread_has_console
- True when the calling thread has an attached console.
- See also
- attach_console/0
- [det]attach_console
- [det]attach_console(+Title)
- Create a new console and make the standard Prolog streams point to it.
If not provided, the title is built using the thread id. Does nothing if
the current thread already has a console attached.
- [det]tspy(:Spec)
- [det]tspy(:Spec,
+ThreadOrClass)
- Trap the graphical debugger on reaching Spec. The predicate tspy/0
enabled debug mode in all threads using tdebug/0
while tspy/1 enables
debug mode using tdebug/1.
- [det]tdebug
- [det]tdebug(+ThreadOrClass)
- [det]tnodebug
- [det]tnodebug(+ThreadOrClass)
- Enable or disable a thread or group of threads for debugging using the
graphical tracer. A group of threads is addressed based on the
class property of a thread set by thread_create/3
or set_thread/2.
This implies loading the graphical tracer and switching the thread to
debug mode using debug/0.
New threads created inherit their debug mode from the thread that
created them.
Thread classes have been introduced in SWI-Prolog 10.0.2/10.1.5. This
allows for more selective debugging as well as ensuring debugging works
in newly created threads. For example, the HTTP server creates all its worker
threads in the class http. Using query below, we
reliable make sure spy points are trapped in HTTP handler threads,
regardless of whether the worker existed or is lazily created and
regardless of whether the user switched to
nodebug mode while tracing a previous event (see
debug_reset_from_class/0).
?- tdebug(http).
- [det]tbacktrace(+Thread)
- [det]tbacktrace(+Thread,
+Options)
- Print a backtrace for Thread to the stream
user_error
of the calling thread. This is achieved by inserting an interrupt into
Thread using call_in_thread/2. Options:
- depth(+MaxFrames)
- Number of stack frames to show. Default is the current Prolog flag
backtrace_depth
or 20.
Other options are passed to get_prolog_backtrace/3.
- bug
- call_in_thread/2
may not process the event.
- [det]tprofile(+Thread)
- Profile the operation of Thread until the user hits a key.
- [det]thread_alias(+Alias)
- Set the alias for a thread.
- deprecated
- Use set_thread/2
using
alias(Alias).
