# Module Netlog.Debug

    module Debug: sig .. end

Controlling messages for debugging Ocamlnet
Many Ocamlnet modules can emit debug messages. For a module `M` (e.g. `Rpc_client`) there is usually a sub module `M.Debug` providing functions controlling the debug messages. These functions send the messages to this `Debug` module, and from here they are forwarded to `Netlog.log` (with a level of ``Debug`).

In this module everything is by default initialized to enable debug messages (i.e., `current_dlogger` is set to `fwd_dlogger`, and this function sends the messages to `current_logger` where they are printed by `channel_logger stderr `Debug`). However, the debugged modules also need to be enabled individually. One can do this by setting the variable `M.Debug.enable` to `true`, or by calling `enable_module` or `enable_all` (see below).

Although this debug interface is mainly intended for Ocamlnet itself, it is not restricted to this. In order to use it for a user module, one has to register the boolean variable that controls whether debug messages are enabled (see `register_module` below). This should be done at module initialization time, and before any thread is spawned.

    type dlogger = string -> string -> unit

Debug logger: The first string is the module name, and the second is the message

    val fwd_dlogger : dlogger

The standard debug logger simply prepends the module name to the message (separated by ": "), and calls the current logger to print it

    val null_dlogger : dlogger

The "logger" not printing anything

    val current_dlogger : dlogger Pervasives.ref

The current debug logger. This is initialized to `fwd_dlogger` at program startup. Set this variable to `null_logger` to completely turn off debug logging of Ocamlnet.

    val log : string -> string -> unit

Writes a log message

    val logf : string -> ('a, unit, string, unit) Pervasives.format4 -> 'a

Writes a log message like `printf`

    val enable_module : string -> unit

    val disable_module : string -> unit

Enable or disable the passed module `M` (e.g. `enable_module "Rpc_client"`). No exception is raised when the module name is invalid! Because of this, it is usually safer to change the variable `M.Debug.enable` directly (e.g. `Rpc_client.Debug.enable := true`).

    val enable_all : unit -> unit

Enable all modules

    val disable_all : unit -> unit

Disable all modules (the default)

    val names : unit -> string list

Return the possible module names for `enable_module` and `disable_module`

## For debugged Ocamlnet modules

    val register_module : string -> bool Pervasives.ref -> unit

Registers the `enable` variable of the named module

    val mk_dlog : string -> bool Pervasives.ref -> string -> unit

`let dlog = mk_dlog "M" enable`: The conditional debug function

    val mk_dlogr : string -> bool Pervasives.ref -> (unit -> string) -> unit

`let dlogr = mk_dlog "M" enable`: The conditional debug function

## File descriptor tracking

`Netlog.Debug` also has a little hash table that maps file descriptors to an info record. This allows it to track file descriptors more easily, and to find file descriptor leaks, and "double close" bugs. All long-living descriptors managed by Ocamlnet should go into this table.

    type serial

A serial number for the optional tracking of ownership

    val new_serial : unit -> serial

Create new serial number

    val track_fd : ?update:bool ->
           ?anchor:'a ->
           ?sn:serial ->
           owner:string -> descr:string -> Unix.file_descr -> unit

`track_fd ~owner ~descr fd`: Enters the descriptor `fd` into the descriptor table. The `owner` string should be set to the module name. In `descr` one can give additional information, e.g. about the purpose, and details like the file name.

It is not an error if there is also an entry for the descriptor `fd`. However, a warning is emitted (using the debug logger). By setting `update` to `true`, this warning can be suppressed. The old entry is overwritten by the new one.

The `anchor` can be an arbitrary boxed value. When the garbage collector calls the finaliser for `anchor` the descriptor is marked as dead, and will be tagged in the `fd_table` as such.

By setting `sn` to a new serial number, the knowledge of this number is required to update the descriptor entry later, and to release the descriptor. If the entry is tried to be updated or released with the wrong serial number, a warning is emitted (to the debug logger).

    val release_fd : ?sn:serial -> ?force:bool -> Unix.file_descr -> unit

Removes this descriptor from the descriptor table.

It is not an error if the descriptor does not exist in the table. However, a warning is emitted (using the debug logger).

`release_fd` must be invoked before the descriptor is actually closed.

`force`: If set, all warnings are suppressed

    val fd_string : ?owner:bool -> ?descr:bool -> Unix.file_descr -> string

Return a string for generating debug messages. By default, the string only includes the numeric descriptor value.

If `owner` is set to true, the string also includes the owner. If `descr` is set to true, the string also includes the description.

The full version of this string looks like "76(Http_client - 87.65.213.67:80)". An untracked descriptor looks like "76(?)".

    val fd_table : unit -> string list

Returns the table of descriptors as list of lines. One can easily print them to stdout using `List.iter print_endline (fd_table())`.

    val enable_fd_tracking : bool Pervasives.ref

By setting to true, each `track_fd` and `release_fd` is logged.