module Printexc: Printexc
typet =
exn
= ..
The type of exception values.
val to_string : exn -> string
Printexc.to_string e
returns a string representation of
the exception e
.
val to_string_default : exn -> string
Printexc.to_string_default e
returns a string representation of the
exception e
, ignoring all registered exception printers.
val print : ('a -> 'b) -> 'a -> 'b
Printexc.print fn x
applies fn
to x
and returns the result.
If the evaluation of fn x
raises any exception, the
name of the exception is printed on standard error output,
and the exception is raised again.
The typical use is to catch and report exceptions that
escape a function application.
val catch : ('a -> 'b) -> 'a -> 'b
Printexc.catch fn x
is similar to Printexc.print
, but
aborts the program with exit code 2 after printing the
uncaught exception. This function is deprecated: the runtime
system is now able to print uncaught exceptions as precisely
as Printexc.catch
does. Moreover, calling Printexc.catch
makes it harder to track the location of the exception
using the debugger or the stack backtrace facility.
So, do not use Printexc.catch
in new code.
val print_backtrace : out_channel -> unit
Printexc.print_backtrace oc
prints an exception backtrace
on the output channel oc
. The backtrace lists the program
locations where the most-recently raised exception was raised
and where it was propagated through function calls.
If the call is not inside an exception handler, the returned backtrace is unspecified. If the call is after some exception-catching code (before in the handler, or in a when-guard during the matching of the exception handler), the backtrace may correspond to a later exception than the handled one.
val get_backtrace : unit -> string
Printexc.get_backtrace ()
returns a string containing the
same exception backtrace that Printexc.print_backtrace
would
print. Same restriction usage than Printexc.print_backtrace
.
val record_backtrace : bool -> unit
Printexc.record_backtrace b
turns recording of exception backtraces
on (if b = true
) or off (if b = false
). Initially, backtraces
are not recorded, unless the b
flag is given to the program
through the OCAMLRUNPARAM
variable.
val backtrace_status : unit -> bool
Printexc.backtrace_status()
returns true
if exception
backtraces are currently recorded, false
if not.
val register_printer : (exn -> string option) -> unit
Printexc.register_printer fn
registers fn
as an exception
printer. The printer should return None
or raise an exception
if it does not know how to convert the passed exception, and Some
with
ss
the resulting string if it can convert the passed
exception. Exceptions raised by the printer are ignored.
When converting an exception into a string, the printers will be invoked
in the reverse order of their registrations, until a printer returns
a Some s
value (if no such printer exists, the runtime will use a
generic printer).
When using this mechanism, one should be aware that an exception backtrace
is attached to the thread that saw it raised, rather than to the exception
itself. Practically, it means that the code related to fn
should not use
the backtrace if it has itself raised an exception before.
val use_printers : exn -> string option
Printexc.use_printers e
returns None
if there are no registered
printers and Some s
with else as the resulting string otherwise.
type
raw_backtrace
The type raw_backtrace
stores a backtrace in a low-level format,
which can be converted to usable form using raw_backtrace_entries
and backtrace_slots_of_raw_entry
below.
Converting backtraces to backtrace_slot
s is slower than capturing the
backtraces. If an application processes many backtraces, it can be useful
to use raw_backtrace
to avoid or delay conversion.
Raw backtraces cannot be marshalled. If you need marshalling, you
should use the array returned by the backtrace_slots
function of
the next section.
typeraw_backtrace_entry = private
int
A raw_backtrace_entry
is an element of a raw_backtrace
.
Each raw_backtrace_entry
is an opaque integer, whose value is not stable
between different programs, or even between different runs of the same
binary.
A raw_backtrace_entry
can be converted to a usable form using
backtrace_slots_of_raw_entry
below. Note that, due to inlining, a
single raw_backtrace_entry
may convert to several backtrace_slot
s.
Since the values of a raw_backtrace_entry
are not stable, they cannot
be marshalled. If they are to be converted, the conversion must be done
by the process that generated them.
Again due to inlining, there may be multiple distinct raw_backtrace_entry
values that convert to equal backtrace_slot
s. However, if two
raw_backtrace_entry
s are equal as integers, then they represent the same
backtrace_slot
s.
val raw_backtrace_entries : raw_backtrace -> raw_backtrace_entry array
val get_raw_backtrace : unit -> raw_backtrace
Printexc.get_raw_backtrace ()
returns the same exception
backtrace that Printexc.print_backtrace
would print, but in
a raw format. Same restriction usage than Printexc.print_backtrace
.
val print_raw_backtrace : out_channel -> raw_backtrace -> unit
Print a raw backtrace in the same format
Printexc.print_backtrace
uses.
val raw_backtrace_to_string : raw_backtrace -> string
Return a string from a raw backtrace, in the same format
Printexc.get_backtrace
uses.
val raise_with_backtrace : exn -> raw_backtrace -> 'a
Reraise the exception using the given raw_backtrace for the origin of the exception
val get_callstack : int -> raw_backtrace
Printexc.get_callstack n
returns a description of the top of the
call stack on the current program point (for the current thread),
with at most n
entries. (Note: this function is not related to
exceptions at all, despite being part of the Printexc
module.)
val default_uncaught_exception_handler : exn -> raw_backtrace -> unit
Printexc.default_uncaught_exception_handler
prints the exception and
backtrace on standard error output.
val set_uncaught_exception_handler : (exn -> raw_backtrace -> unit) -> unit
Printexc.set_uncaught_exception_handler fn
registers fn
as the handler
for uncaught exceptions. The default handler is
Printexc.default_uncaught_exception_handler
.
Note that when fn
is called all the functions registered with
at_exit
have already been called. Because of this you must
make sure any output channel fn
writes on is flushed.
Also note that exceptions raised by user code in the interactive toplevel are not passed to this function as they are caught by the toplevel itself.
If fn
raises an exception, both the exceptions passed to fn
and raised
by fn
will be printed with their respective backtrace.
These functions are used to traverse the slots of a raw backtrace and extract information from them in a programmer-friendly format.
type
backtrace_slot
The abstract type backtrace_slot
represents a single slot of
a backtrace.
val backtrace_slots : raw_backtrace -> backtrace_slot array option
Returns the slots of a raw backtrace, or None
if none of them
contain useful information.
In the return array, the slot at index 0
corresponds to the most
recent function call, raise, or primitive get_backtrace
call in
the trace.
Some possible reasons for returning None
are as follow:
-g
)ocamlc -g
)val backtrace_slots_of_raw_entry : raw_backtrace_entry -> backtrace_slot array option
Returns the slots of a single raw backtrace entry, or None
if this
entry lacks debug information.
Slots are returned in the same order as backtrace_slots
: the slot
at index 0
is the most recent call, raise, or primitive, and
subsequent slots represent callers.
type
location = {
|
filename : |
|||
|
line_number : |
|||
|
start_char : |
|||
|
end_char : |
|||
|
end_line : |
(* |
| *) |
|
end_col : |
(* |
| *) |
}
The type of location information found in backtraces. start_char
and end_char
are positions relative to the beginning of line_number
.
end_col
is relative to the beginning of end_line
.
module Slot:sig
..end
type
raw_backtrace_slot
This type is used to iterate over the slots of a raw_backtrace
.
For most purposes, backtrace_slots_of_raw_entry
is easier to use.
Like raw_backtrace_entry
, values of this type are process-specific and
must absolutely not be marshalled, and are unsafe to use for this reason
(marshalling them may not fail, but un-marshalling and using the result
will result in undefined behavior).
Elements of this type can still be compared and hashed: when two elements are equal, then they represent the same source location (the converse is not necessarily true in presence of inlining, for example).
val raw_backtrace_length : raw_backtrace -> int
raw_backtrace_length bckt
returns the number of slots in the
backtrace bckt
.
val get_raw_backtrace_slot : raw_backtrace -> int -> raw_backtrace_slot
get_raw_backtrace_slot bckt pos
returns the slot in position pos
in the
backtrace bckt
.
val convert_raw_backtrace_slot : raw_backtrace_slot -> backtrace_slot
Extracts the user-friendly backtrace_slot
from a low-level
raw_backtrace_slot
.
val get_raw_backtrace_next_slot : raw_backtrace_slot -> raw_backtrace_slot option
get_raw_backtrace_next_slot slot
returns the next slot inlined, if any.
Sample code to iterate over all frames (inlined and non-inlined):
(* Iterate over inlined frames *)
let rec iter_raw_backtrace_slot f slot =
f slot;
match get_raw_backtrace_next_slot slot with
| None -> ()
| Some slot' -> iter_raw_backtrace_slot f slot'
(* Iterate over stack frames *)
let iter_raw_backtrace f bt =
for i = 0 to raw_backtrace_length bt - 1 do
iter_raw_backtrace_slot f (get_raw_backtrace_slot bt i)
done
val exn_slot_id : exn -> int
Printexc.exn_slot_id
returns an integer which uniquely identifies
the constructor used to create the exception value exn
(in the current runtime).
val exn_slot_name : exn -> string
Printexc.exn_slot_name exn
returns the internal name of the constructor
used to create the exception value exn
.