Dynamic loading of compiled files

val loadfile : string -> unit

In bytecode: load the given bytecode object file ( .cmo file) or bytecode library file ( .cma file), and link it with the running program. In native code: load the given OCaml plugin file (usually .cmxs ), and link it with the running program.

All toplevel expressions in the loaded compilation units are evaluated. No facilities are provided to access value names defined by the unit. Therefore, the unit must itself register its entry points with the main program (or a previously-loaded library) e.g. by modifying tables of functions.

An exception will be raised if the given library defines toplevel modules whose names clash with modules existing either in the main program or a shared library previously loaded with loadfile . Modules from shared libraries previously loaded with loadfile_private are not included in this restriction.

The compilation units loaded by this function are added to the "allowed units" list (see Dynlink.set_allowed_units ).

val loadfile_private : string -> unit

Same as loadfile , except that the compilation units just loaded are hidden (cannot be referenced) from other modules dynamically loaded afterwards.

An exception will be raised if the given library defines toplevel modules whose names clash with modules existing in either the main program or a shared library previously loaded with loadfile . Modules from shared libraries previously loaded with loadfile_private are not included in this restriction.

An exception will also be raised if the given library defines toplevel modules whose name matches that of an interface depended on by a module existing in either the main program or a shared library previously loaded with loadfile . This applies even if such dependency is only a "module alias" dependency (i.e. just on the name rather than the contents of the interface).

The compilation units loaded by this function are not added to the "allowed units" list (see Dynlink.set_allowed_units ) since they cannot be referenced from other compilation units.

val adapt_filename : string -> string

In bytecode, the identity function. In native code, replace the last extension with .cmxs .

Access control

val set_allowed_units : string list -> unit

Set the list of compilation units that may be referenced from units that are dynamically loaded in the future to be exactly the given value.

Initially all compilation units composing the program currently running are available for reference from dynamically-linked units. set_allowed_units can be used to restrict access to a subset of these units, e.g. to the units that compose the API for dynamically-linked code, and prevent access to all other units, e.g. private, internal modules of the running program.

Note that Dynlink.loadfile changes the allowed-units list.

val allow_only : string list -> unit

allow_only units sets the list of allowed units to be the intersection of the existing allowed units and the given list of units. As such it can never increase the set of allowed units.

val prohibit : string list -> unit

prohibit units prohibits dynamically-linked units from referencing the units named in list units by removing such units from the allowed units list. This can be used to prevent access to selected units, e.g. private, internal modules of the running program.

val main_program_units : unit -> string list

Return the list of compilation units that form the main program (i.e. are not dynamically linked).

val public_dynamically_loaded_units : unit -> string list

Return the list of compilation units that have been dynamically loaded via loadfile (and not via loadfile_private ). Note that compilation units loaded dynamically cannot be unloaded.

val all_units : unit -> string list

Return the list of compilation units that form the main program together with those that have been dynamically loaded via loadfile (and not via loadfile_private ).

val allow_unsafe_modules : bool -> unit

Govern whether unsafe object files are allowed to be dynamically linked. A compilation unit is 'unsafe' if it contains declarations of external functions, which can break type safety. By default, dynamic linking of unsafe object files is not allowed. In native code, this function does nothing; object files with external functions are always allowed to be dynamically linked.

Error reporting

type linking_error = private
| Undefined_global of string
| Unavailable_primitive of string
| Uninitialized_global of string

type error = private
| Not_a_bytecode_file of string
| Inconsistent_import of string
| Unavailable_unit of string
| Unsafe_file
| Linking_error of string * linking_error
| Corrupted_interface of string
| Cannot_open_dynamic_library of exn
| Library's_module_initializers_failed of exn
| Inconsistent_implementation of string
| Module_already_loaded of string
| Private_library_cannot_implement_interface of string

exception Error of error

Errors in dynamic linking are reported by raising the Error exception with a description of the error. A common case is the dynamic library not being found on the system: this is reported via Cannot_open_dynamic_library (the enclosed exception may be platform-specific).

val error_message : error -> string

Convert an error description to a printable message.