code(3)

NAME
code - Interface to the Erlang code server process.

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 interactive or embedded mode. Which one is decided by the command-line flag -mode:

    % erl -mode embedded

The modes are as follows:

    • In interactive mode, which is default, only the modules needed by the runtime system are loaded during system startup. Other code is dynamically loaded when first referenced. When a call to a function in a certain module is made, and that module is not loaded, the code server searches for and tries to load that module.

    • In embedded mode, modules are not auto-loaded. Trying to use a module that has not been loaded results in an error. This mode is recommended when the boot script loads all modules, as it is typically done in OTP releases. (Code can still be loaded later by explicitly ordering the code server to do so).

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 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 appear 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

The code paths specified by $OTPROOT, ERL_LIBS, and boot scripts have their listings cached by default (except for ".") The code server will lookup the contents in their directories once and avoid future file system traversals. Therefore, modules added to such directories after the Erlang VM boots will not be picked up. This behaviour can be disabled by setting -cache_boot_paths false or by calling code:set_path(code:get_path()).

CHANGE: The support for caching directories in the code path was added in Erlang/OTP 26.

Directories given by the command line options -pa and -pz are not cached by default. Many of the functions that manipulate the code path accept the cache atom as an optional argument to enable caching selectively.

  Loading of Code From Archive Files

CHANGE: The existing experimental support for archive files will be changed in a future release. As of Erlang/OTP 27, the function code:lib_dir/2, the -code_path_choice flag, and using erl_prim_loader for reading files from an archive are deprecated. escript scripts that use archive files should use escript:extract/2 to read data files from its archive instead of using code:lib_dir/2 and erl_prim_loader.

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.

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 escript.

A future-proof way for escript scripts to read data files from the archive is to use the escript:extract/2 function.

When the choice of directories in the code path is strict (which is the default as of Erlang/OTP 27), 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 has changed to strict in OTP 27 and the option is scheduled for removal in OTP 28. See module init in the Erts application.

  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.

When a new instance of the module is loaded, 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 executed 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 executed 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.

  Native Coverage Support

In runtime systems that use the JIT, native coverage is a light-weight way to find out which functions or lines that have been executed, or how many times each function or line has been executed.

CHANGE: The support for native coverage was added in Erlang/OTP 27.

Native coverage works by instrumenting code at load-time. When a module has been instrumented for native coverage collection it is not possible to later disable the coverage collection, except by reloading the module. However, the overhead for keeping coverage collection running is often neligible, especially for coverage mode function that only keeps track of which functions that have been executed.

The cover tool in the Tools application will automatically use the native coverage support if the runtime system supports it.

It is only necessary to use the functionality described next if cover is not sufficient, for example:

    • If one wants to collect coverage information for the code that runs when the runtime system is starting (module init and so on). cover can only be used when the Erlang system has started, and it will reload every module that is to be analyzed.

    • If it is necessary to collect coverage information with the absolute minimum disturbance of the test system. cover always counts how many times each line is executed (coverage mode line_counters), but by using native coverage one can use a less expensive coverage mode such as function, which has almost negligible overhead.

Short summary of using native coverage

If the line or line_counters coverage mode is to be used, the code to be tested must be compiled with option line_coverage.

Use set_coverage_mode(Mode) to set a coverage mode for all code subsequently loaded, or set it with option +JPcover for erl.

Optionally reset coverage information for all modules that are to be tested by calling reset_coverage(Module).

Run the code whose coverage information is to be collected.

Read out the counters for all interesting modules by calling get_coverage(Level, Module), where Level is either function or line.

The other native coverage BIFs

The following BIFs are sometimes useful, for example to fail gracefully if the runtime system does not support native coverage:

    • coverage_support() - check whether the runtime system supports native coverage

    • get_coverage_mode() - get the current coverage mode

    • get_coverage_mode(Module) - get the coverage mode for module Module

  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

add_path_ret() :: true | {error, bad_directory}.
cache() :: cache | nocache.
coverage_mode() :: none | function | function_counters | line | line_counters.
debug_frame()
debug_info()
debug_line()
debug_name()
debug_source()
debug_value()
load_error_rsn() :: badfile | nofile | not_purged | on_load_failure | sticky_directory.
load_ret() :: {error, What :: load_error_rsn()} | {module, Module :: module()}.
loaded_filename() :: (Filename :: file:filename()) | loaded_ret_atoms().
loaded_ret_atoms() :: cover_compiled | preloaded.
module_status() :: not_loaded | loaded | modified | removed.
-opaque prepared_code()

    An opaque term holding prepared code.
replace_path_ret() :: true | {error, bad_directory | bad_name | {badarg, _}}.
set_path_ret() :: true | {error, bad_directory}.

FUNCTIONS

add_patha(Dir, cache()) -> add_path_ret() when Dir :: file:filename().

    Adds Dir to the beginning of the code path.

    If Dir exists, it is removed from the old position in the code path.

    Argument Cache controls whether the content of the directory should be cached on first traversal. If Cache is cache the directory contents will be cached; if Cache is nocache it will not be cached.

    Returns true if successful, or {error, bad_directory} if Dir is not the name of a directory.
add_pathsa(Dirs, cache()) -> ok when 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 Dirs is [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.

    Argument Cache controls whether the content of the directory should be cached on first traversal. If Cache is cache the directory contents will be cached; if Cache is nocache it will not be cached.

    Always returns ok, regardless of the validity of each individual Dir.
add_pathsz(Dirs, cache()) -> ok when Dirs :: [Dir :: file:filename()].

    Adds the directories in Dirs to the end of the code path.

    Directories that are already present in the path will not be added.

    Argument Cache controls whether the content of the directory should be cached on first traversal. If Cache is cache the directory contents will be cached; if Cache is nocache it will not be cached.

    Always returns ok, regardless of the validity of each individual Dir.
add_pathz(Dir, cache()) -> add_path_ret() when Dir :: file:filename().

    Adds Dir as the directory last in the code path.

    If Dir already exists in the path, it is not added.

    Argument Cache controls whether the content of the directory should be cached on first traversal. If Cache is cache the directory contents will be cached; if Cache is nocache it will not be cached.

    Returns true if successful, or {error, bad_directory} if Dir is not the name of a directory.
all_available() -> [{Module, Filename, Loaded}] when Module :: string(), Filename :: loaded_filename(), Loaded :: boolean().

    Returns a list of tuples {Module, Filename, Loaded} for all available modules.

    A module is considered to be available if it either is loaded or would be loaded if called. Filename is normally the absolute filename, as described for is_loaded/1.
all_loaded() -> [{Module, Loaded}] when Module :: module(), Loaded :: loaded_filename().

    Returns a list of tuples {Module, Loaded} for all loaded modules.

    Loaded is normally the absolute filename, as described for is_loaded/1.
atomic_load(Modules) -> ok | {error, [{Module, What}]} when 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 cannot 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.
clash() -> ok.

    Searches all directories in the code path for module names with identical names and writes a report to stdout.
clear_cache() -> ok.

    Clears the code path cache.

    If a directory is cached, its cache is cleared once and then it will be recalculated and cached once more in a future traversal.

    To clear the cache for a single path, either re-add it to the code path (with add_path/2) or replace it (with replace_path/3). To disable all caching, reset the code path with code:set_path(code:get_path()).

    Always returns ok.
compiler_dir() -> file:filename().

    Returns the compiler library directory.

    Equivalent to code:lib_dir(compiler).
coverage_support() -> Supported when Supported :: boolean().

    Returns true if the system supports coverage and false otherwise.

    See also: Native Coverage Support
del_path(NameOrDir) -> boolean() | {error, What} when 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 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
del_paths(NamesOrDirs) -> ok when NamesOrDirs :: [Name | Dir], Name :: atom(), Dir :: file:filename().

    Deletes directories from the code path.

    The argument is a list of either atoms or complete directory names. If Name is an atom, the directory with the name .../Name-Vsn is deleted from the code path.

    Always returns ok, regardless of the validity of each individual NamesOrDirs.
delete(Module) -> boolean() when 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.
ensure_loaded(Module) -> {module, Module} | {error, What} when 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.

    If called concurrently, this function ensures that only one process attempts to load said module at a given time.

    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.
ensure_modules_loaded([Module]) -> ok | {error, [{Module, What}]} when 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.

    Unlike ensure_loaded/1, modules are loaded even in embedded mode.

    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.
finish_loading(Prepared) -> ok | {error, [{Module, What}]} when 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 cannot 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.
get_coverage(Level, module()) -> Result when Level :: function | line | cover_id_line, Result :: [{Entity, CoverageInfo}], Entity :: {Function, Arity} | Line | CoverId, CoverageInfo :: Covered | Counter, Function :: atom(), Arity :: arity(), Line :: non_neg_integer(), CoverId :: pos_integer(), Covered :: boolean(), Counter :: non_neg_integer().

    Return either function or line coverage data for module Module.

    If Level is function, returns function coverage for the given module according to its coverage mode: function
        For each function in module Module, a boolean indicating whether that function has been executed at least once is returned.
    function_counters
        For each function in module Module, an integer giving the number of times that line has been executed is returned.
    line
        For each function in module Module, a boolean indicating whether that function has been executed at least once is returned.
    line_counters
        For each function in module Module, a boolean indicating whether that function has been executed at least once is returned (note that in this mode, counters for the number of times each function has been executed cannot be retrieved).

    If Level is line, returns line coverage for the given module according to its coverage mode: line
        For each executable line in the module, a boolean indicating whether that line has been executed at least once is returned.
    line_counters
        For each executable line in the module, an integer giving the number of times that line was executed is returned.

    Level cover_id_line is used by the cover tool.

    Failures: badarg
        If Level is not function or line.
    badarg
        If Module is not an atom.
    badarg
        If Module does not refer to a loaded module.
    badarg
        If Module was not loaded in another coverage mode than none.
    badarg
        If Level is line and Module has not been loaded with either line or line_counters enabled.
    badarg
        If the runtime system does not support coverage.

    See also: Native Coverage Support
get_coverage_mode() -> Mode when Mode :: coverage_mode().

    Returns the coverage mode as set by option +JPcover for erl or set_coverage_mode/1.

    Failure: badarg
        If the runtime system does not support coverage.

    See also: Native Coverage Support
get_coverage_mode(Module) -> Mode when Module :: module(), Mode :: coverage_mode().

    Get coverage mode for the given module.

    Failures: badarg
        If Module is not an atom.
    badarg
        If Module does not refer to a loaded module.
    badarg
        If the runtime system does not support coverage.

    See also: Native Coverage Support
get_doc(Mod) -> {ok, Res} | {error, Reason} when Mod :: module(), Res :: #docs_v1{}, Reason :: non_existing | missing | file:posix().

    Returns EEP 48 style documentation for Module if available.

    If Module is not found in the code path, this function returns {error,non_existing}.

    If no documentation can be found this function attempts to generate documentation from the debug information in the module. If no debug information is available, this function returns {error,missing}.

    For more information about the documentation chunk see Documentation Storage and Format in Kernel's User's Guide.
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.
get_object_code(Module) -> {Module, Binary, Filename} | error when Module :: module(), Binary :: binary(), Filename :: file:filename().

    Returns the object code for module Module if found in the code path.

    Returns {Module, Binary, Filename} if successful, otherwise error. Binary is a binary data object, which contains the object code for the module. This is 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),
        erpc:call(Node, code, load_binary, [Module, Filename, Binary]),
get_path() -> Path when Path :: [Dir :: file:filename()].

    Returns the code path.
is_loaded(Module) -> {file, Loaded} | false when Module :: module(), Loaded :: loaded_filename().

    Checks whether 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(4)), Loaded =:= preloaded. If the module is Cover-compiled (see cover), Loaded =:= cover_compiled.
is_sticky(Module) -> boolean() when 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.
lib_dir() -> file:filename().

    Returns the library directory, $OTPROOT/lib, where $OTPROOT is the root directory of Erlang/OTP.

    Example:

        1> code:lib_dir().
        "/usr/local/otp/lib"
lib_dir(Name) -> file:filename() | {error, bad_name} when Name :: atom().

    Returns the path for the library directory, the top directory, for an application Name located under $OTPROOT/lib or in 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.

    WARNING: Archives are experimental. In a future release, they can be removed or their behavior can change.

    Example:

        > code:lib_dir(mnesia).
        "/usr/local/otp/lib/mnesia-4.23"

    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} when Name :: atom(), SubDir :: atom().

    Deprecated: code:lib_dir/2 is deprecated; this functionality will be removed in a future release

    Returns the path to a subdirectory directly under the top directory of an application.

    CHANGE: This function is part of the archive support, which is an experimental feature that will be changed or removed in a future release.

    Normally the subdirectories reside under the top directory for the application, but when applications at least partly reside in an archive, the situation is different. Some of the subdirectories can reside as regular directories while others reside in an archive file. It is not checked whether this directory exists.

    Instead of using this function, use code:lib_dir/1 and filename:join/2.

    Example:

        1> filename:join(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.
load_abs(Filename) -> load_ret() when Filename :: file:filename().

    Equivalent to load_file(Module), except that 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.
load_binary(Module, Filename, Binary) -> {module, Module} | {error, What} when Module :: module(), Filename :: loaded_filename(), Binary :: binary(), What :: badarg | load_error_rsn().

    Loads object code from a binary.

    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 originates. 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.
load_file(Module) -> load_ret() when 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. Use load_binary/3 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.
modified_modules() -> [module()].

    Returns the list of all currently loaded modules for which module_status/1 returns modified.

    See also all_loaded/0.
module_status() -> [{module(), module_status()}].

    See module_status/1 and all_loaded/0 for details.
module_status(Module :: module() | [module()]) -> module_status() | [{module(), module_status()}].

    Returns the status of Module in relation to object file on disk.

    The status of a module can be one of: 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.

    See also modified_modules/0.
objfile_extension() -> nonempty_string().

    Returns the object code file extension corresponding to the Erlang machine used.

    For the official Erlang/OTP release, the return value is always .beam.
prepare_loading(Modules) -> {ok, Prepared} | {error, [{Module, What}]} when 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.
priv_dir(Name) -> file:filename() | {error, bad_name} when Name :: atom().

    Returns the path to the priv directory in an application.

    WARNING: For backward compatibility, Name is also allowed to be a string. That will probably change in a future release.
purge(Module) -> boolean() when 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.

    CHANGE: As of Erlang/OTP 20.0, 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 whether a process is lingering.

    Returns true if successful and any process is needed to be killed, otherwise false.
replace_path(Name, Dir, cache()) -> replace_path_ret() when Name :: atom(), Dir :: file:filename().

    Replaces an old occurrence of a directory named .../Name-Vsn 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. This function is to be used if a new version of the directory (library) is added to a running system.

    Argument Cache controls whether the content of the directory should be cached on first traversal. If Cache is cache the directory contents will be cached; if Cache is nocache it will not be cached.

    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
reset_coverage(Module) -> ok when Module :: module().

    Resets coverage information for module Module.

    If the coverage mode is either function or line, all booleans for Module keeping track of executed functions or lines are set to false.

    If the coverage mode is either function_counters or line_counters, all counters for Module are reset to zero.

    Failures: badarg
        If Module is not an atom.
    badarg
        If Module does not refer to a loaded module.
    badarg
        If Module was not loaded with coverage enabled.
    badarg
        If the runtime system does not support coverage.

    See also: Native Coverage Support
root_dir() -> file:filename().

    Returns the root directory of Erlang/OTP, which is the directory where it is installed.

    Example:

        1> code:root_dir().
        "/usr/local/otp"
set_coverage_mode(Mode) -> OldMode when Mode :: coverage_mode(), OldMode :: coverage_mode().

    Sets the coverage mode for modules that are subsequently loaded, similar to option +JPcover for erl.

    The coverage mode will have the following effect on code that is loaded following this call: function
        All modules that are loaded will be instrumented to keep track of which functions are executed. Information about which functions that have been executed can be retrieved by calling get_coverage(function, Module).
    function_counters
        All modules that are loaded will be instrumented to count how many times each function is executed. Information about how many times each function has been executed can be retrieved by calling get_coverage(function, Module).
    line
        When modules that have been compiled with the line_coverage option are loaded, they will be instrumented to keep track of which lines have been executed. Information about which lines have been executed can be retrieved by calling get_coverage(line, Module), and information about which functions that have been executed can be retrieved by calling get_coverage(function, Module).
    line_counters
        When modules that have been compiled with the line_coverage option are loaded, they will be instrumented to count the number of times each line is executed. Information about how many times each line has been executed can be retrieved by calling get_coverage(line, Module), and information about which functions that have been executed can be retrieved by calling get_coverage(function, Module) (note that in this mode, counters for the number of times each function has been executed cannot be retrieved).
    none
        Modules will be loaded without coverage instrumentation.

    Returns the previous coverage mode.

    Failures: badarg
        If Mode is not a valid coverage mode.
    badarg
        If the runtime system does not support coverage.

    See also: Native Coverage Support
set_path(Path, cache()) -> set_path_ret() when Path :: [Dir :: file:filename()].

    Sets the code path to the list of directories Path.

    Argument Cache controls whether the content of the directory should be cached on first traversal. If Cache is cache the directory contents will be cached; if Cache is nocache it will not be cached.

    Returns: true
        If successful
    {error, bad_directory}
        If any Dir is not a directory name
soft_purge(Module) -> boolean() when Module :: module().

    Purges the code for Module, that is, removes code marked as old, but only if no processes linger in it.

    CHANGE: As of Erlang/OTP 20.0, 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 whether a process is lingering.

    Returns false if the module cannot be purged because of processes lingering in old code, otherwise true.
stick_dir(Dir) -> ok | error when Dir :: file:filename().

    Marks Dir as sticky.

    Returns ok if successful, otherwise error.
unstick_dir(Dir) -> ok | error when Dir :: file:filename().

    Unsticks a directory that is marked as sticky.

    Returns ok if successful, otherwise error.
where_is_file(Filename) -> non_existing | Absname when Filename :: file:filename(), Absname :: file:filename().

    Searches the code path for Filename, which is 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.
which(Module) -> Which when Module :: module(), Which :: loaded_filename() | non_existing.

    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.