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NAME
code - Erlang code server.
DESCRIPTION
This module contains the interface to the Erlang code server, which deals with the loading
of compiled code into a running Erlang runtime system.
The runtime system can be started in embedded or interactive mode. Which one is decided by
command-line flag -mode:
% erl -mode interactive
The modes are as follows:
* In embedded mode, all code is loaded during system startup according to the boot
script. (Code can also be loaded later by explicitly ordering the code server to do
so).
* In interactive mode, which is default, only some code is loaded during system startup,
basically the modules needed by the runtime system. Other code is dynamically loaded
when first referenced. When a call to a function in a certain module is made, and the
module is not loaded, the code server searches for and tries to load the module.
To prevent accidentally reloading of modules affecting the Erlang runtime system,
directories kernel, stdlib, and compiler are considered sticky. This means that the system
issues a warning and rejects the request if a user tries to reload a module residing in
any of them. The feature can be disabled by using command-line flag -nostick.
CODE PATH
In interactive mode, the code server maintains a search path, usually called the code
path, consisting of a list of directories, which it searches sequentially when trying to
load a module.
Initially, the code path consists of the current working directory and all Erlang object
code directories under library directory $OTPROOT/lib, where $OTPROOT is the installation
directory of Erlang/OTP, code:root_dir(). Directories can be named Name[-Vsn] and the code
server, by default, chooses the directory with the highest version number among those
having the same Name. Suffix -Vsn is optional. If an ebin directory exists under
Name[-Vsn], this directory is added to the code path.
Environment variable ERL_LIBS (defined in the operating system) can be used to define more
library directories to be handled in the same way as the standard OTP library directory
described above, except that directories without an ebin directory are ignored.
All application directories found in the additional directories appears before the
standard OTP applications, except for the Kernel and STDLIB applications, which are placed
before any additional applications. In other words, modules found in any of the additional
library directories override modules with the same name in OTP, except for modules in
Kernel and STDLIB.
Environment variable ERL_LIBS (if defined) is to contain a colon-separated (for Unix-like
systems) or semicolon-separated (for Windows) list of additional libraries.
Example:
On a Unix-like system, ERL_LIBS can be set to the following
/usr/local/jungerl:/home/some_user/my_erlang_lib
On Windows, use semi-colon as separator.
LOADING OF CODE FROM ARCHIVE FILES
Warning:
The support for loading code from archive files is experimental. The purpose of releasing
it before it is ready is to obtain early feedback. The file format, semantics, interfaces,
and so on, can be changed in a future release. The function lib_dir/2 and flag
-code_path_choice are also experimental.
The Erlang archives are ZIP files with extension .ez. Erlang archives can also be enclosed
in escript files whose file extension is arbitrary.
Erlang archive files can contain entire Erlang applications or parts of applications. The
structure in an archive file is the same as the directory structure for an application. If
you, for example, create an archive of mnesia-4.4.7, the archive file must be named
mnesia-4.4.7.ez and it must contain a top directory named mnesia-4.4.7. If the version
part of the name is omitted, it must also be omitted in the archive. That is, a mnesia.ez
archive must contain a mnesia top directory.
An archive file for an application can, for example, be created like this:
zip:create("mnesia-4.4.7.ez",
["mnesia-4.4.7"],
[{cwd, code:lib_dir()},
{compress, all},
{uncompress,[".beam",".app"]}]).
Any file in the archive can be compressed, but to speed up the access of frequently read
files, it can be a good idea to store beam and app files uncompressed in the archive.
Normally the top directory of an application is located in library directory $OTPROOT/lib
or in a directory referred to by environment variable ERL_LIBS. At startup, when the
initial code path is computed, the code server also looks for archive files in these
directories and possibly adds ebin directories in archives to the code path. The code path
then contains paths to directories that look like $OTPROOT/lib/mnesia.ez/mnesia/ebin or
$OTPROOT/lib/mnesia-4.4.7.ez/mnesia-4.4.7/ebin.
The code server uses module erl_prim_loader in ERTS (possibly through erl_boot_server) to
read code files from archives. However, the functions in erl_prim_loader can also be used
by other applications to read files from archives. For example, the call
erl_prim_loader:list_dir( "/otp/root/lib/mnesia-4.4.7.ez/mnesia-4.4.7/examples/bench)"
would list the contents of a directory inside an archive. See erl_prim_loader(3erl).
An application archive file and a regular application directory can coexist. This can be
useful when it is needed to have parts of the application as regular files. A typical case
is the priv directory, which must reside as a regular directory to link in drivers
dynamically and start port programs. For other applications that do not need this,
directory priv can reside in the archive and the files under the directory priv can be
read through erl_prim_loader.
When a directory is added to the code path and when the entire code path is (re)set, the
code server decides which subdirectories in an application that are to be read from the
archive and which that are to be read as regular files. If directories are added or
removed afterwards, the file access can fail if the code path is not updated (possibly to
the same path as before, to trigger the directory resolution update).
For each directory on the second level in the application archive (ebin, priv, src, and so
on), the code server first chooses the regular directory if it exists and second from the
archive. Function code:lib_dir/2 returns the path to the subdirectory. For example,
code:lib_dir(megaco,ebin) can return /otp/root/lib/megaco-3.9.1.1.ez/megaco-3.9.1.1/ebin
while code:lib_dir(megaco,priv) can return /otp/root/lib/megaco-3.9.1.1/priv.
When an escript file contains an archive, there are no restrictions on the name of the
escript and no restrictions on how many applications that can be stored in the embedded
archive. Single Beam files can also reside on the top level in the archive. At startup,
the top directory in the embedded archive and all (second level) ebin directories in the
embedded archive are added to the code path. See erts:escript(1).
When the choice of directories in the code path is strict, the directory that ends up in
the code path is exactly the stated one. This means that if, for example, the directory
$OTPROOT/lib/mnesia-4.4.7/ebin is explicitly added to the code path, the code server does
not load files from $OTPROOT/lib/mnesia-4.4.7.ez/mnesia-4.4.7/ebin.
This behavior can be controlled through command-line flag -code_path_choice Choice. If the
flag is set to relaxed, the code server instead chooses a suitable directory depending on
the actual file structure. If a regular application ebin directory exists, it is chosen.
Otherwise, the directory ebin in the archive is chosen if it exists. If neither of them
exists, the original directory is chosen.
Command-line flag -code_path_choice Choice also affects how module init interprets the
boot script. The interpretation of the explicit code paths in the boot script can be
strict or relaxed. It is particularly useful to set the flag to relaxed when elaborating
with code loading from archives without editing the boot script. The default is relaxed.
See erts:init(3erl).
CURRENT AND OLD CODE
The code for a module can exist in two variants in a system: current code and old code.
When a module is loaded into the system for the first time, the module code becomes
'current' and the global export table is updated with references to all functions exported
from the module.
If then a new instance of the module is loaded (for example, because of error correction),
the code of the previous instance becomes 'old', and all export entries referring to the
previous instance are removed. After that, the new instance is loaded as for the first
time, and becomes 'current'.
Both old and current code for a module are valid, and can even be evaluated concurrently.
The difference is that exported functions in old code are unavailable. Hence, a global
call cannot be made to an exported function in old code, but old code can still be
evaluated because of processes lingering in it.
If a third instance of the module is loaded, the code server removes (purges) the old code
and any processes lingering in it are terminated. Then the third instance becomes
'current' and the previously current code becomes 'old'.
For more information about old and current code, and how to make a process switch from old
to current code, see section Compilation and Code Loading in the Erlang Reference Manual.
ARGUMENT TYPES AND INVALID ARGUMENTS
Module and application names are atoms, while file and directory names are strings. For
backward compatibility reasons, some functions accept both strings and atoms, but a future
release will probably only allow the arguments that are documented.
Functions in this module generally fail with an exception if they are passed an incorrect
type (for example, an integer or a tuple where an atom is expected). An error tuple is
returned if the argument type is correct, but there are some other errors (for example, a
non-existing directory is specified to set_path/1).
ERROR REASONS FOR CODE-LOADING FUNCTIONS
Functions that load code (such as load_file/1) will return {error,Reason} if the load
operation fails. Here follows a description of the common reasons.
badfile:
The object code has an incorrect format or the module name in the object code is not
the expected module name.
nofile:
No file with object code was found.
not_purged:
The object code could not be loaded because an old version of the code already
existed.
on_load_failure:
The module has an -on_load function that failed when it was called.
sticky_directory:
The object code resides in a sticky directory.
DATA TYPES
load_ret() =
{error, What :: load_error_rsn()} |
{module, Module :: module()}
load_error_rsn() =
badfile |
nofile |
not_purged |
on_load_failure |
sticky_directory
prepared_code()
An opaque term holding prepared code.
EXPORTS
set_path(Path) -> true | {error, What}
Types:
Path = [Dir :: file:filename()]
What = bad_directory
Sets the code path to the list of directories Path.
Returns:
true:
If successful
{error, bad_directory}:
If any Dir is not a directory name
get_path() -> Path
Types:
Path = [Dir :: file:filename()]
Returns the code path.
add_path(Dir) -> add_path_ret()
add_pathz(Dir) -> add_path_ret()
Types:
Dir = file:filename()
add_path_ret() = true | {error, bad_directory}
Adds Dir to the code path. The directory is added as the last directory in the new
path. If Dir already exists in the path, it is not added.
Returns true if successful, or {error, bad_directory} if Dir is not the name of a
directory.
add_patha(Dir) -> add_path_ret()
Types:
Dir = file:filename()
add_path_ret() = true | {error, bad_directory}
Adds Dir to the beginning of the code path. If Dir exists, it is removed from the
old position in the code path.
Returns true if successful, or {error, bad_directory} if Dir is not the name of a
directory.
add_paths(Dirs) -> ok
add_pathsz(Dirs) -> ok
Types:
Dirs = [Dir :: file:filename()]
Adds the directories in Dirs to the end of the code path. If a Dir exists, it is
not added.
Always returns ok, regardless of the validity of each individual Dir.
add_pathsa(Dirs) -> ok
Types:
Dirs = [Dir :: file:filename()]
Traverses Dirs and adds each Dir to the beginning of the code path. This means that
the order of Dirs is reversed in the resulting code path. For example, if you add
[Dir1,Dir2], the resulting path will be [Dir2,Dir1|OldCodePath].
If a Dir already exists in the code path, it is removed from the old position.
Always returns ok, regardless of the validity of each individual Dir.
del_path(NameOrDir) -> boolean() | {error, What}
Types:
NameOrDir = Name | Dir
Name = atom()
Dir = file:filename()
What = bad_name
Deletes a directory from the code path. The argument can be an atom Name, in which
case the directory with the name .../Name[-Vsn][/ebin] is deleted from the code
path. Also, the complete directory name Dir can be specified as argument.
Returns:
true:
If successful
false:
If the directory is not found
{error, bad_name}:
If the argument is invalid
replace_path(Name, Dir) -> true | {error, What}
Types:
Name = atom()
Dir = file:filename()
What = bad_directory | bad_name | {badarg, term()}
Replaces an old occurrence of a directory named .../Name[-Vsn][/ebin] in the code
path, with Dir. If Name does not exist, it adds the new directory Dir last in the
code path. The new directory must also be named .../Name[-Vsn][/ebin]. This
function is to be used if a new version of the directory (library) is added to a
running system.
Returns:
true:
If successful
{error, bad_name}:
If Name is not found
{error, bad_directory}:
If Dir does not exist
{error, {badarg, [Name, Dir]}}:
If Name or Dir is invalid
load_file(Module) -> load_ret()
Types:
Module = module()
load_ret() =
{error, What :: load_error_rsn()} |
{module, Module :: module()}
Tries to load the Erlang module Module, using the code path. It looks for the
object code file with an extension corresponding to the Erlang machine used, for
example, Module.beam. The loading fails if the module name found in the object code
differs from the name Module. load_binary/3 must be used to load object code with a
module name that is different from the file name.
Returns {module, Module} if successful, or {error, Reason} if loading fails. See
Error Reasons for Code-Loading Functions for a description of the possible error
reasons.
load_abs(Filename) -> load_ret()
Types:
Filename = file:filename()
load_ret() =
{error, What :: load_error_rsn()} |
{module, Module :: module()}
loaded_filename() =
(Filename :: file:filename()) | loaded_ret_atoms()
loaded_ret_atoms() = cover_compiled | preloaded
Same as load_file(Module), but Filename is an absolute or relative filename. The
code path is not searched. It returns a value in the same way as load_file/1.
Notice that Filename must not contain the extension (for example, .beam) because
load_abs/1 adds the correct extension.
ensure_loaded(Module) -> {module, Module} | {error, What}
Types:
Module = module()
What = embedded | badfile | nofile | on_load_failure
Tries to load a module in the same way as load_file/1, unless the module is already
loaded. However, in embedded mode it does not load a module that is not already
loaded, but returns {error, embedded} instead. See Error Reasons for Code-Loading
Functions for a description of other possible error reasons.
load_binary(Module, Filename, Binary) ->
{module, Module} | {error, What}
Types:
Module = module()
Filename = loaded_filename()
Binary = binary()
What = badarg | load_error_rsn()
loaded_filename() =
(Filename :: file:filename()) | loaded_ret_atoms()
loaded_ret_atoms() = cover_compiled | preloaded
This function can be used to load object code on remote Erlang nodes. Argument
Binary must contain object code for Module. Filename is only used by the code
server to keep a record of from which file the object code for Module comes. Thus,
Filename is not opened and read by the code server.
Returns {module, Module} if successful, or {error, Reason} if loading fails. See
Error Reasons for Code-Loading Functions for a description of the possible error
reasons.
atomic_load(Modules) -> ok | {error, [{Module, What}]}
Types:
Modules = [Module | {Module, Filename, Binary}]
Module = module()
Filename = file:filename()
Binary = binary()
What =
badfile |
nofile |
on_load_not_allowed |
duplicated |
not_purged |
sticky_directory |
pending_on_load
Tries to load all of the modules in the list Modules atomically. That means that
either all modules are loaded at the same time, or none of the modules are loaded
if there is a problem with any of the modules.
Loading can fail for one the following reasons:
badfile:
The object code has an incorrect format or the module name in the object code
is not the expected module name.
nofile:
No file with object code exists.
on_load_not_allowed:
A module contains an -on_load function.
duplicated:
A module is included more than once in Modules.
not_purged:
The object code can not be loaded because an old version of the code already
exists.
sticky_directory:
The object code resides in a sticky directory.
pending_on_load:
A previously loaded module contains an -on_load function that never finished.
If it is important to minimize the time that an application is inactive while
changing code, use prepare_loading/1 and finish_loading/1 instead of atomic_load/1.
Here is an example:
{ok,Prepared} = code:prepare_loading(Modules),
%% Put the application into an inactive state or do any
%% other preparation needed before changing the code.
ok = code:finish_loading(Prepared),
%% Resume the application.
prepare_loading(Modules) ->
{ok, Prepared} | {error, [{Module, What}]}
Types:
Modules = [Module | {Module, Filename, Binary}]
Module = module()
Filename = file:filename()
Binary = binary()
Prepared = prepared_code()
What = badfile | nofile | on_load_not_allowed | duplicated
Prepares to load the modules in the list Modules. Finish the loading by calling
finish_loading(Prepared).
This function can fail with one of the following error reasons:
badfile:
The object code has an incorrect format or the module name in the object code
is not the expected module name.
nofile:
No file with object code exists.
on_load_not_allowed:
A module contains an -on_load function.
duplicated:
A module is included more than once in Modules.
finish_loading(Prepared) -> ok | {error, [{Module, What}]}
Types:
Prepared = prepared_code()
Module = module()
What = not_purged | sticky_directory | pending_on_load
Tries to load code for all modules that have been previously prepared by
prepare_loading/1. The loading occurs atomically, meaning that either all modules
are loaded at the same time, or none of the modules are loaded.
This function can fail with one of the following error reasons:
not_purged:
The object code can not be loaded because an old version of the code already
exists.
sticky_directory:
The object code resides in a sticky directory.
pending_on_load:
A previously loaded module contains an -on_load function that never finished.
ensure_modules_loaded(Modules :: [Module]) ->
ok | {error, [{Module, What}]}
Types:
Module = module()
What = badfile | nofile | on_load_failure
Tries to load any modules not already loaded in the list Modules in the same way as
load_file/1.
Returns ok if successful, or {error,[{Module,Reason}]} if loading of some modules
fails. See Error Reasons for Code-Loading Functions for a description of other
possible error reasons.
delete(Module) -> boolean()
Types:
Module = module()
Removes the current code for Module, that is, the current code for Module is made
old. This means that processes can continue to execute the code in the module, but
no external function calls can be made to it.
Returns true if successful, or false if there is old code for Module that must be
purged first, or if Module is not a (loaded) module.
purge(Module) -> boolean()
Types:
Module = module()
Purges the code for Module, that is, removes code marked as old. If some processes
still linger in the old code, these processes are killed before the code is
removed.
Note:
As of ERTS version 9.0, a process is only considered to be lingering in the code if
it has direct references to the code. For more information see documentation of
erlang:check_process_code/3, which is used in order to determine this.
Returns true if successful and any process is needed to be killed, otherwise false.
soft_purge(Module) -> boolean()
Types:
Module = module()
Purges the code for Module, that is, removes code marked as old, but only if no
processes linger in it.
Note:
As of ERTS version 9.0, a process is only considered to be lingering in the code if
it has direct references to the code. For more information see documentation of
erlang:check_process_code/3, which is used in order to determine this.
Returns false if the module cannot be purged because of processes lingering in old
code, otherwise true.
is_loaded(Module) -> {file, Loaded} | false
Types:
Module = module()
Loaded = loaded_filename()
loaded_filename() =
(Filename :: file:filename()) | loaded_ret_atoms()
Filename is an absolute filename.
loaded_ret_atoms() = cover_compiled | preloaded
Checks if Module is loaded. If it is, {file, Loaded} is returned, otherwise false.
Normally, Loaded is the absolute filename Filename from which the code is obtained.
If the module is preloaded (see script(5)), Loaded==preloaded. If the module is
Cover-compiled (see cover(3erl)), Loaded==cover_compiled.
all_loaded() -> [{Module, Loaded}]
Types:
Module = module()
Loaded = loaded_filename()
loaded_filename() =
(Filename :: file:filename()) | loaded_ret_atoms()
Filename is an absolute filename.
loaded_ret_atoms() = cover_compiled | preloaded
Returns a list of tuples {Module, Loaded} for all loaded modules. Loaded is
normally the absolute filename, as described for is_loaded/1.
which(Module) -> Which
Types:
Module = module()
Which = file:filename() | loaded_ret_atoms() | non_existing
loaded_ret_atoms() = cover_compiled | preloaded
If the module is not loaded, this function searches the code path for the first
file containing object code for Module and returns the absolute filename.
If the module is loaded, it returns the name of the file containing the loaded
object code.
If the module is preloaded, preloaded is returned.
If the module is Cover-compiled, cover_compiled is returned.
If the module cannot be found, non_existing is returned.
get_object_code(Module) -> {Module, Binary, Filename} | error
Types:
Module = module()
Binary = binary()
Filename = file:filename()
Searches the code path for the object code of module Module. Returns {Module,
Binary, Filename} if successful, otherwise error. Binary is a binary data object,
which contains the object code for the module. This can be useful if code is to be
loaded on a remote node in a distributed system. For example, loading module Module
on a node Node is done as follows:
...
{_Module, Binary, Filename} = code:get_object_code(Module),
rpc:call(Node, code, load_binary, [Module, Filename, Binary]),
...
root_dir() -> file:filename()
Returns the root directory of Erlang/OTP, which is the directory where it is
installed.
Example:
> code:root_dir().
"/usr/local/otp"
lib_dir() -> file:filename()
Returns the library directory, $OTPROOT/lib, where $OTPROOT is the root directory
of Erlang/OTP.
Example:
> code:lib_dir().
"/usr/local/otp/lib"
lib_dir(Name) -> file:filename() | {error, bad_name}
Types:
Name = atom()
Returns the path for the "library directory", the top directory, for an application
Name located under $OTPROOT/lib or on a directory referred to with environment
variable ERL_LIBS.
If a regular directory called Name or Name-Vsn exists in the code path with an ebin
subdirectory, the path to this directory is returned (not the ebin directory).
If the directory refers to a directory in an archive, the archive name is stripped
away before the path is returned. For example, if directory
/usr/local/otp/lib/mnesia-4.2.2.ez/mnesia-4.2.2/ebin is in the path,
/usr/local/otp/lib/mnesia-4.2.2/ebin is returned. This means that the library
directory for an application is the same, regardless if the application resides in
an archive or not.
Example:
> code:lib_dir(mnesia).
"/usr/local/otp/lib/mnesia-4.2.2"
Returns {error, bad_name} if Name is not the name of an application under
$OTPROOT/lib or on a directory referred to through environment variable ERL_LIBS.
Fails with an exception if Name has the wrong type.
Warning:
For backward compatibility, Name is also allowed to be a string. That will probably
change in a future release.
lib_dir(Name, SubDir) -> file:filename() | {error, bad_name}
Types:
Name = SubDir = atom()
Returns the path to a subdirectory directly under the top directory of an
application. Normally the subdirectories reside under the top directory for the
application, but when applications at least partly resides in an archive, the
situation is different. Some of the subdirectories can reside as regular
directories while other reside in an archive file. It is not checked whether this
directory exists.
Example:
> code:lib_dir(megaco, priv).
"/usr/local/otp/lib/megaco-3.9.1.1/priv"
Fails with an exception if Name or SubDir has the wrong type.
compiler_dir() -> file:filename()
Returns the compiler library directory. Equivalent to code:lib_dir(compiler).
priv_dir(Name) -> file:filename() | {error, bad_name}
Types:
Name = atom()
Returns the path to the priv directory in an application. Equivalent to
code:lib_dir(Name, priv).
Warning:
For backward compatibility, Name is also allowed to be a string. That will probably
change in a future release.
objfile_extension() -> nonempty_string()
Returns the object code file extension corresponding to the Erlang machine used,
namely .beam.
stick_dir(Dir) -> ok | error
Types:
Dir = file:filename()
Marks Dir as sticky.
Returns ok if successful, otherwise error.
unstick_dir(Dir) -> ok | error
Types:
Dir = file:filename()
Unsticks a directory that is marked as sticky.
Returns ok if successful, otherwise error.
is_sticky(Module) -> boolean()
Types:
Module = module()
Returns true if Module is the name of a module that has been loaded from a sticky
directory (in other words: an attempt to reload the module will fail), or false if
Module is not a loaded module or is not sticky.
where_is_file(Filename) -> non_existing | Absname
Types:
Filename = Absname = file:filename()
Searches the code path for Filename, a file of arbitrary type. If found, the full
name is returned. non_existing is returned if the file cannot be found. The
function can be useful, for example, to locate application resource files.
clash() -> ok
Searches all directories in the code path for module names with identical names and
writes a report to stdout.
module_status(Module :: module()) ->
not_loaded | loaded | modified | removed
Returns:
not_loaded:
If Module is not currently loaded.
loaded:
If Module is loaded and the object file exists and contains the same code.
removed:
If Module is loaded but no corresponding object file can be found in the code
path.
modified:
If Module is loaded but the object file contains code with a different MD5
checksum.
Preloaded modules are always reported as loaded, without inspecting the contents on
disk. Cover compiled modules will always be reported as modified if an object file
exists, or as removed otherwise. Modules whose load path is an empty string (which
is the convention for auto-generated code) will only be reported as loaded or
not_loaded.
For modules that have native code loaded (see is_module_native/1), the MD5 sum of
the native code in the object file is used for the comparison, if it exists; the
Beam code in the file is ignored. Reversely, for modules that do not currently have
native code loaded, any native code in the file will be ignored.
See also modified_modules/0.
modified_modules() -> [module()]
Returns the list of all currently loaded modules for which module_status/1 returns
modified. See also all_loaded/0.
is_module_native(Module) -> true | false | undefined
Types:
Module = module()
Returns:
true:
If Module is the name of a loaded module that has native code loaded
false:
If Module is loaded but does not have native code
undefined:
If Module is not loaded
get_mode() -> embedded | interactive
Returns an atom describing the mode of the code server: interactive or embedded.
This information is useful when an external entity (for example, an IDE) provides
additional code for a running node. If the code server is in interactive mode, it
only has to add the path to the code. If the code server is in embedded mode, the
code must be loaded with load_binary/3.