*

A native function that crash will crash the whole VM.

*

An erroneously implemented native function can cause a VM internal state inconsistency, which can cause a crash of the VM, or miscellaneous misbehaviors of the VM at any point after the call to the native function.

*

A native function doing lengthy work before returning degrades responsiveness of the VM, and can cause miscellaneous strange behaviors. Such strange behaviors include, but are not limited to, extreme memory usage, and bad load balancing between schedulers. Strange behaviors that can occur because of lengthy work can also vary between Erlang/OTP releases.

Read and write Erlang terms:

Any Erlang terms can be passed to a NIF as function arguments and be returned as function return values. The terms are of C-type ERL_NIF_TERM and can only be read or written using API functions. Most functions to read the content of a term are prefixed enif_get_ and usually return true (or false) if the term is of the expected type (or not). The functions to write terms are all prefixed enif_make_ and usually return the created ERL_NIF_TERM. There are also some functions to query terms, like enif_is_atom, enif_is_identical, and enif_compare.

Binaries:

Terms of type binary are accessed with the help of struct type ErlNifBinary, which contains a pointer (data) to the raw binary data and the length (size) of the data in bytes. Both data and size are read-only and are only to be written using calls to API functions. Instances of ErlNifBinary are, however, always allocated by the user (usually as local variables).

Resource objects:

The use of resource objects is a safe way to return pointers to native data structures from a NIF. A resource object is only a block of memory allocated with enif_alloc_resource. A handle ("safe pointer") to this memory block can then be returned to Erlang by the use of enif_make_resource. The term returned by enif_make_resource is opaque in nature. It can be stored and passed between processes, but the only real end usage is to pass it back as an argument to a NIF. The NIF can then call enif_get_resource and get back a pointer to the memory block, which is guaranteed to still be valid. A resource object is not deallocated until the last handle term is garbage collected by the VM and the resource is released with enif_release_resource (not necessarily in that order).

ERL_NIF_TERM term;
MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct));
/* initialize struct ... */
term = enif_make_resource(env, obj);
if (keep_a_reference_of_our_own) {
    /* store 'obj' in static variable, private data or other resource object */
}
else {
    enif_release_resource(obj);
    /* resource now only owned by "Erlang" */
}
return term;

Module upgrade and static data:

A loaded NIF library is tied to the Erlang module instance that loaded it. If the module is upgraded, the new module instance needs to load its own NIF library (or maybe choose not to). The new module instance can, however, choose to load the exact same NIF library as the old code if it wants to. Sharing the dynamic library means that static data defined by the library is shared as well. To avoid unintentionally shared static data between module instances, each Erlang module version can keep its own private data. This private data can be set when the NIF library is loaded and later retrieved by calling enif_priv_data.

Threads and concurrency:

A NIF is thread-safe without any explicit synchronization as long as it acts as a pure function and only reads the supplied arguments. When you write to a shared state either through static variables or enif_priv_data, you need to supply your own explicit synchronization. This includes terms in process independent environments that are shared between threads. Resource objects also require synchronization if you treat them as mutable.

Version Management:

When a NIF library is built, information about the NIF API version is compiled into the library. When a NIF library is loaded, the runtime system verifies that the library is of a compatible version. erl_nif.h defines the following:

Time Measurement:

Support for time measurement in NIF libraries:

I/O Queues:

The Erlang nif library contains function for easily working with I/O vectors as used by the unix system call writev. The I/O Queue is not thread safe, so some other synchronization mechanism has to be used.

int writeiovec(ErlNifEnv *env, ERL_NIF_TERM term, ERL_NIF_TERM *tail,
               ErlNifIOQueue *q, int fd) {
    ErlNifIOVec vec, *iovec = &vec;
    SysIOVec *sysiovec;
    int saved_errno;
    int iovcnt, n;
    if (!enif_inspect_iovec(env, 64, term, tail, &iovec))
        return -2;
    if (enif_ioq_size(q) > 0) {
        /* If the I/O queue contains data we enqueue the iovec and
           then peek the data to write out of the queue. */
        if (!enif_ioq_enqv(q, iovec, 0))
            return -3;
        sysiovec = enif_ioq_peek(q, &iovcnt);
    } else {
        /* If the I/O queue is empty we skip the trip through it. */
        iovcnt = iovec->iovcnt;
        sysiovec = iovec->iov;
    }
    /* Attempt to write the data */
    n = writev(fd, sysiovec, iovcnt);
    saved_errno = errno;
    if (enif_ioq_size(q) == 0) {
        /* If the I/O queue was initially empty we enqueue any
           remaining data into the queue for writing later. */
        if (n >= 0 && !enif_ioq_enqv(q, iovec, n))
            return -3;
    } else {
        /* Dequeue any data that was written from the queue. */
        if (n > 0 && !enif_ioq_deq(q, n, NULL))
            return -4;
    }
    /* return n, which is either number of bytes written or -1 if
       some error happened */
    errno = saved_errno;
    return n;
}

Long-running NIFs:

As mentioned in the warning text at the beginning of this manual page, it is of vital importance that a native function returns relatively fast. It is difficult to give an exact maximum amount of time that a native function is allowed to work, but usually a well-behaving native function is to return to its caller within 1 millisecond. This can be achieved using different approaches. If you have full control over the code to execute in the native function, the best approach is to divide the work into multiple chunks of work and call the native function multiple times. This is, however, not always possible, for example when calling third-party libraries.

ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, NULL, upgrade, unload):

This is the magic macro to initialize a NIF library. It is to be evaluated in global file scope.

int (*load)(ErlNifEnv* caller_env, void** priv_data, ERL_NIF_TERM load_info):

load is called when the NIF library is loaded and no previously loaded library exists for this module.

int (*upgrade)(ErlNifEnv* caller_env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info):

upgrade is called when the NIF library is loaded and there is old code of this module with a loaded NIF library.

void (*unload)(ErlNifEnv* caller_env, void* priv_data):

unload is called when the module code that the NIF library belongs to is purged as old. New code of the same module may or may not exist.

ERL_NIF_TERM:

Variables of type ERL_NIF_TERM can refer to any Erlang term. This is an opaque type and values of it can only by used either as arguments to API functions or as return values from NIFs. All ERL_NIF_TERMs belong to an environment (ErlNifEnv). A term cannot be destructed individually, it is valid until its environment is destructed.

ErlNifEnv:

ErlNifEnv represents an environment that can host Erlang terms. All terms in an environment are valid as long as the environment is valid. ErlNifEnv is an opaque type; pointers to it can only be passed on to API functions. Three types of environments exist:

ErlNifFunc:

typedef struct {
    const char* name;
    unsigned arity;
    ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
    unsigned flags;
} ErlNifFunc;

ErlNifBinary:

typedef struct {
    unsigned size;
    unsigned char* data;
} ErlNifBinary;

ErlNifBinaryToTerm:

An enumeration of the options that can be specified to enif_binary_to_term. For default behavior, use value 0.

ErlNifMonitor:

This is an opaque data type that identifies a monitor.

ErlNifPid:

A process identifier (pid). In contrast to pid terms (instances of ERL_NIF_TERM), ErlNifPids are self-contained and not bound to any environment. ErlNifPid is an opaque type.

ErlNifPort:

A port identifier. In contrast to port ID terms (instances of ERL_NIF_TERM), ErlNifPorts are self-contained and not bound to any environment. ErlNifPort is an opaque type.

ErlNifResourceType:

Each instance of ErlNifResourceType represents a class of memory-managed resource objects that can be garbage collected. Each resource type has a unique name and a destructor function that is called when objects of its type are released.

ErlNifResourceTypeInit:

typedef struct {
    ErlNifResourceDtor* dtor;
    ErlNifResourceStop* stop;
    ErlNifResourceDown* down;
} ErlNifResourceTypeInit;

ErlNifResourceDtor:

typedef void ErlNifResourceDtor(ErlNifEnv* caller_env, void* obj);

ErlNifResourceDown:

typedef void ErlNifResourceDown(ErlNifEnv* caller_env, void* obj, ErlNifPid* pid, ErlNifMonitor* mon);

ErlNifResourceStop:

typedef void ErlNifResourceStop(ErlNifEnv* caller_env, void* obj, ErlNifEvent event, int is_direct_call);

ErlNifCharEncoding:

typedef enum {
    ERL_NIF_LATIN1
}ErlNifCharEncoding;

ErlNifSysInfo:

Used by enif_system_info to return information about the runtime system. Contains the same content as ErlDrvSysInfo.

ErlNifSInt64:

A native signed 64-bit integer type.

ErlNifUInt64:

A native unsigned 64-bit integer type.

ErlNifTime:

A signed 64-bit integer type for representation of time.

ErlNifTimeUnit:

An enumeration of time units supported by the NIF API:

ErlNifUniqueInteger:

An enumeration of the properties that can be requested from enif_make_unique_integer. For default properties, use value 0.

ErlNifHash:

An enumeration of the supported hash types that can be generated using enif_hash.

SysIOVec:

A system I/O vector, as used by writev on Unix and WSASend on Win32. It is used in ErlNifIOVec and by enif_ioq_peek.

ErlNifIOVec:

typedef struct {
  int iovcnt;
  size_t size;
  SysIOVec* iov;
} ErlNifIOVec;

ErlNifIOQueueOpts:

Options to configure a ErlNifIOQueue.

Allocates memory of size bytes.

Returns NULL if the allocation fails.

The returned pointer is suitably aligned for any built-in type that fit in the allocated memory.

Allocates a new binary of size size bytes. Initializes the structure pointed to by bin to refer to the allocated binary. The binary must either be released by enif_release_binary or ownership transferred to an Erlang term with enif_make_binary. An allocated (and owned) ErlNifBinary can be kept between NIF calls.

If you do not need to reallocate or keep the data alive across NIF calls, consider using enif_make_new_binary instead as it will allocate small binaries on the process heap when possible.

Returns true on success, or false if allocation fails.

Allocates a new process independent environment. The environment can be used to hold terms that are not bound to any process. Such terms can later be copied to a process environment with enif_make_copy or be sent to a process as a message with enif_send.

Returns pointer to the new environment.

Allocates a memory-managed resource object of type type and size size bytes.

Creates a term that is the result of decoding the binary data at data, which must be encoded according to the Erlang external term format. No more than size bytes are read from data. Argument opts corresponds to the second argument to erlang:binary_to_term/2 and must be either 0 or ERL_NIF_BIN2TERM_SAFE.

On success, stores the resulting term at *term and returns the number of bytes read. Returns 0 if decoding fails or if opts is invalid.

See also ErlNifBinaryToTerm, erlang:binary_to_term/2, and enif_term_to_binary.

Frees all terms in an environment and clears it for reuse. The environment must have been allocated with enif_alloc_env.

Returns an integer < 0 if lhs < rhs, 0 if lhs = rhs, and > 0 if lhs > rhs. Corresponds to the Erlang operators ==, /=, =<, <, >=, and > (but not =:= or =/=).

Compares two ErlNifMonitors. Can also be used to imply some artificial order on monitors, for whatever reason.

Returns 0 if monitor1 and monitor2 are equal, < 0 if monitor1 < monitor2, and > 0 if monitor1 > monitor2.

Same as erl_drv_cond_broadcast.

Same as erl_drv_cond_create.

Same as erl_drv_cond_destroy.

Same as erl_drv_cond_name.

Same as erl_drv_cond_signal.

Same as erl_drv_cond_wait.

Gives the runtime system a hint about how much CPU time the current NIF call has consumed since the last hint, or since the start of the NIF if no previous hint has been specified. The time is specified as a percent of the timeslice that a process is allowed to execute Erlang code until it can be suspended to give time for other runnable processes. The scheduling timeslice is not an exact entity, but can usually be approximated to about 1 millisecond.

Notice that it is up to the runtime system to determine if and how to use this information. Implementations on some platforms can use other means to determine consumed CPU time. Lengthy NIFs should regardless of this frequently call enif_consume_timeslice to determine if it is allowed to continue execution.

Argument percent must be an integer between 1 and 100. This function must only be called from a NIF-calling thread, and argument env must be the environment of the calling process.

Returns 1 if the timeslice is exhausted, otherwise 0. If 1 is returned, the NIF is to return as soon as possible in order for the process to yield.

This function is provided to better support co-operative scheduling, improve system responsiveness, and make it easier to prevent misbehaviors of the VM because of a NIF monopolizing a scheduler thread. It can be used to divide length work into a number of repeated NIF calls without the need to create threads.

See also the warning text at the beginning of this manual page.

Converts the val value of time unit from to the corresponding value of time unit to. The result is rounded using the floor function.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument.

See also ErlNifTime and ErlNifTimeUnit.

Returns the CPU time in the same format as erlang:timestamp(). The CPU time is the time the current logical CPU has spent executing since some arbitrary point in the past. If the OS does not support fetching this value, enif_cpu_time invokes enif_make_badarg.

Cancels a monitor created earlier with enif_monitor_process. Argument obj is a pointer to the resource holding the monitor and *mon identifies the monitor.

Argument caller_env is the environment of the calling process or callback. Must only be NULL if calling from a custom thread.

Returns 0 if the monitor was successfully identified and removed. Returns a non-zero value if the monitor could not be identified, which means it was either

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Same as erl_drv_equal_tids.

Similar to fprintf but this format string also accepts "%T", which formats Erlang terms of type ERL_NIF_TERM.

This function is primarily intended for debugging purpose. It is not recommended to print very large terms with %T. The function may change errno, even if successful.

Frees memory allocated by enif_alloc.

Frees an environment allocated with enif_alloc_env. All terms created in the environment are freed as well.

Frees an io vector returned from enif_inspect_iovec. This is needed only if a NULL environment is passed to enif_inspect_iovec.

ErlNifIOVec *iovec = NULL;
size_t max_elements = 128;
ERL_NIF_TERM tail;
if (!enif_inspect_iovec(NULL, max_elements, term, &tail, &iovec))
  return 0;
// Do things with the iovec
/* Free the iovector, possibly in another thread or nif function call */
enif_free_iovec(iovec);

Writes a NULL-terminated string in the buffer pointed to by buf of size size, consisting of the string representation of the atom term with encoding encode.

Returns the number of bytes written (including terminating NULL character) or 0 if term is not an atom with maximum length of size-1.

Sets *len to the length (number of bytes excluding terminating NULL character) of the atom term with encoding encode.

Returns true on success, or false if term is not an atom.

Sets *dp to the floating-point value of term.

Returns true on success, or false if term is not a float.

Sets *ip to the integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of type int.

Sets *ip to the integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of a signed 64-bit integer.

If term is the pid of a node local process, this function initializes the pid variable *pid from it and returns true. Otherwise returns false. No check is done to see if the process is alive.

If term identifies a node local port, this function initializes the port variable *port_id from it and returns true. Otherwise returns false. No check is done to see if the port is alive.

Sets *head and *tail from list list.

Returns true on success, or false if it is not a list or the list is empty.

Sets *len to the length of list term.

Returns true on success, or false if term is not a proper list.

Sets *ip to the long integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of type long int.

Sets *size to the number of key-value pairs in the map term.

Returns true on success, or false if term is not a map.

Sets *value to the value associated with key in the map map.

Returns true on success, or false if map is not a map or if map does not contain key.

Sets *objp to point to the resource object referred to by term.

Returns true on success, or false if term is not a handle to a resource object of type type.

Writes a NULL-terminated string in the buffer pointed to by buf with size size, consisting of the characters in the string list. The characters are written using encoding encode.

Returns one of the following:

The written string is always NULL-terminated, unless buffer size is < 1.

If term is a tuple, this function sets *array to point to an array containing the elements of the tuple, and sets *arity to the number of elements. Notice that the array is read-only and (*array)[N-1] is the Nth element of the tuple. *array is undefined if the arity of the tuple is zero.

Returns true on success, or false if term is not a tuple.

Sets *ip to the unsigned integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of type unsigned int.

Sets *ip to the unsigned integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of an unsigned 64-bit integer.

Sets *ip to the unsigned long integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of type unsigned long.

Same as erl_drv_getenv.

Returns true if a pending exception is associated with the environment env. If reason is a NULL pointer, ignore it. Otherwise, if a pending exception associated with env exists, set *reason to the value of the exception term. For example, if enif_make_badarg is called to set a pending badarg exception, a later call to enif_has_pending_exception(env, &reason) sets *reason to the atom badarg, then return true.

See also enif_make_badarg and enif_raise_exception.

Hashes term according to the specified ErlNifHash type.

Ranges of taken salt (if any) and returned value depend on the hash type.

Initializes the structure pointed to by bin with information about binary term bin_term.

Returns true on success, or false if bin_term is not a binary.

Initializes the structure pointed to by bin with a continuous buffer with the same byte content as iolist. As with inspect_binary, the data pointed to by bin is transient and does not need to be released.

Returns true on success, or false if iolist is not an iolist.

Fills iovec with the list of binaries provided in iovec_term. The number of elements handled in the call is limited to max_elements, and tail is set to the remainder of the list. Note that the output may be longer than max_elements on some platforms.

To create a list of binaries from an arbitrary iolist, use erlang:iolist_to_iovec/1.

When calling this function, iovec should contain a pointer to NULL or a ErlNifIOVec structure that should be used if possible. e.g.

/* Don't use a pre-allocated structure */
ErlNifIOVec *iovec = NULL;
enif_inspect_iovec(env, max_elements, term, &tail, &iovec);
/* Use a stack-allocated vector as an optimization for vectors with few elements */
ErlNifIOVec vec, *iovec = &vec;
enif_inspect_iovec(env, max_elements, term, &tail, &iovec);

The contents of the iovec is valid until the called nif function returns. If the iovec should be valid after the nif call returns, it is possible to call this function with a NULL environment. If no environment is given the iovec owns the data in the vector and it has to be explicitly freed using enif_free_iovec.

Returns true on success, or false if iovec_term not an iovec.

Create a new I/O Queue that can be used to store data. opts has to be set to ERL_NIF_IOQ_NORMAL.

Destroy the I/O queue and free all of it's contents

Dequeue count bytes from the I/O queue. If size is not NULL, the new size of the queue is placed there.

Returns true on success, or false if the I/O does not contain count bytes. On failure the queue is left un-altered.

Enqueue the bin into q skipping the first skip bytes.

Returns true on success, or false if skip is greater than the size of bin. Any ownership of the binary data is transferred to the queue and bin is to be considered read-only for the rest of the NIF call and then as released.

Enqueue the iovec into q skipping the first skip bytes.

Returns true on success, or false if skip is greater than the size of iovec.

Get the I/O queue as a pointer to an array of SysIOVecs. It also returns the number of elements in iovlen.

Nothing is removed from the queue by this function, that must be done with enif_ioq_deq.

The returned array is suitable to use with the Unix system call writev.

Get the head of the IO Queue as a binary term.

If size is not NULL, the size of the head is placed there.

Nothing is removed from the queue by this function, that must be done with enif_ioq_deq.

Returns true on success, or false if the queue is empty.

Get the size of q.

Returns true if term is an atom.

Returns true if term is a binary.

Returns true if the currently executing process is currently alive, otherwise false.

This function can only be used from a NIF-calling thread, and with an environment corresponding to currently executing processes.

Returns true if term is an empty list.

Return true if term is an exception.

Returns true if term is a fun.

Returns true if the two terms are identical. Corresponds to the Erlang operators =:= and =/=.

Returns true if term is a list.

Returns true if term is a map, otherwise false.

Returns true if term is a number.

Returns true if term is a pid.

Returns true if term is a port.

Returns true if port_id is alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Returns true if pid is alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Returns true if term is a reference.

Returns true if term is a tuple.

Adds a reference to resource object obj obtained from enif_alloc_resource. Each call to enif_keep_resource for an object must be balanced by a call to enif_release_resource before the object is destructed.

Creates an atom term from the NULL-terminated C-string name with ISO Latin-1 encoding. If the length of name exceeds the maximum length allowed for an atom (255 characters), enif_make_atom invokes enif_make_badarg.

Create an atom term from the string name with length len. NULL characters are treated as any other characters. If len exceeds the maximum length allowed for an atom (255 characters), enif_make_atom invokes enif_make_badarg.

Makes a badarg exception to be returned from a NIF, and associates it with environment env. Once a NIF or any function it calls invokes enif_make_badarg, the runtime ensures that a badarg exception is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.

The return value from enif_make_badarg can be used only as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception, but not to any other NIF API function.

See also enif_has_pending_exception and enif_raise_exception.

Makes a binary term from bin. Any ownership of the binary data is transferred to the created term and bin is to be considered read-only for the rest of the NIF call and then as released.

Makes a copy of term src_term. The copy is created in environment dst_env. The source term can be located in any environment.

Creates a floating-point term from a double. If argument double is not finite or is NaN, enif_make_double invokes enif_make_badarg.

Tries to create the term of an already existing atom from the NULL-terminated C-string name with encoding encode.

If the atom already exists, this function stores the term in *atom and returns true, otherwise false. Also returns false if the length of name exceeds the maximum length allowed for an atom (255 characters).

Tries to create the term of an already existing atom from the string name with length len and encoding encode. NULL characters are treated as any other characters.

If the atom already exists, this function stores the term in *atom and returns true, otherwise false. Also returns false if len exceeds the maximum length allowed for an atom (255 characters).

Creates an integer term.

Creates an integer term from a signed 64-bit integer.

Creates an ordinary list term of length cnt. Expects cnt number of arguments (after cnt) of type ERL_NIF_TERM as the elements of the list.

Returns an empty list if cnt is 0.

Creates an ordinary list term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_list to get a compile-time error if the number of arguments does not match.

Creates a list cell [head | tail].

Creates an ordinary list containing the elements of array arr of length cnt.

Returns an empty list if cnt is 0.

Creates an integer term from a long int.

Makes a copy of map map_in and inserts key with value. If key already exists in map_in, the old associated value is replaced by value.

If successful, this function sets *map_out to the new map and returns true. Returns false if map_in is not a map.

The map_in term must belong to environment env.

If map map_in contains key, this function makes a copy of map_in in *map_out, and removes key and the associated value. If map map_in does not contain key, *map_out is set to map_in.

Returns true on success, or false if map_in is not a map.

The map_in term must belong to environment env.

Makes a copy of map map_in and replace the old associated value for key with new_value.

If successful, this function sets *map_out to the new map and returns true. Returns false if map_in is not a map or if it does not contain key.

The map_in term must belong to environment env.

Makes a map term from the given keys and values.

If successful, this function sets *map_out to the new map and returns true. Returns false there are any duplicate keys.

All keys and values must belong to env.

Allocates a binary of size size bytes and creates an owning term. The binary data is mutable until the calling NIF returns. This is a quick way to create a new binary without having to use ErlNifBinary. The drawbacks are that the binary cannot be kept between NIF calls and it cannot be reallocated.

Returns a pointer to the raw binary data and sets *termp to the binary term.

Makes an empty map term.

Makes a pid term from *pid.

Creates a reference like erlang:make_ref/0.

Creates an opaque handle to a memory-managed resource object obtained by enif_alloc_resource. No ownership transfer is done, as the resource object still needs to be released by enif_release_resource. However, notice that the call to enif_release_resource can occur immediately after obtaining the term from enif_make_resource, in which case the resource object is deallocated when the term is garbage collected. For more details, see the example of creating and returning a resource object in the User's Guide.

Before ERTS 9.0 (OTP-20.0), all resource terms did compare equal to each other and to empty binaries (<<>>). If serialized, they would be recreated as plain empty binaries.

Creates a binary term that is memory-managed by a resource object obj obtained by enif_alloc_resource. The returned binary term consists of size bytes pointed to by data. This raw binary data must be kept readable and unchanged until the destructor of the resource is called. The binary data can be stored external to the resource object, in which case the destructor is responsible for releasing the data.

Several binary terms can be managed by the same resource object. The destructor is not called until the last binary is garbage collected. This can be useful to return different parts of a larger binary buffer.

As with enif_make_resource, no ownership transfer is done. The resource still needs to be released with enif_release_resource.

Sets *list_out to the reverse list of the list list_in and returns true, or returns false if list_in is not a list.

This function is only to be used on short lists, as a copy is created of the list, which is not released until after the NIF returns.

The list_in term must belong to environment env.

Creates a list containing the characters of the NULL-terminated string string with encoding encoding.

Creates a list containing the characters of the string string with length len and encoding encoding. NULL characters are treated as any other characters.

Makes a subbinary of binary bin_term, starting at zero-based position pos with a length of size bytes. bin_term must be a binary or bitstring. pos+size must be less or equal to the number of whole bytes in bin_term.

Creates a tuple term of arity cnt. Expects cnt number of arguments (after cnt) of type ERL_NIF_TERM as the elements of the tuple.

Creates a tuple term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_tuple to get a compile-time error if the number of arguments does not match.

Creates a tuple containing the elements of array arr of length cnt.

Creates an integer term from an unsigned int.

Creates an integer term from an unsigned 64-bit integer.

Creates an integer term from an unsigned long int.

Returns a unique integer with the same properties as specified by erlang:unique_integer/1.

env is the environment to create the integer in.

ERL_NIF_UNIQUE_POSITIVE and ERL_NIF_UNIQUE_MONOTONIC can be passed as the second argument to change the properties of the integer returned. They can be combined by OR:ing the two values together.

See also ErlNifUniqueInteger.

Creates an iterator for the map map by initializing the structure pointed to by iter. Argument entry determines the start position of the iterator: ERL_NIF_MAP_ITERATOR_FIRST or ERL_NIF_MAP_ITERATOR_LAST.

Returns true on success, or false if map is not a map.

A map iterator is only useful during the lifetime of environment env that the map belongs to. The iterator must be destroyed by calling enif_map_iterator_destroy:

ERL_NIF_TERM key, value;
ErlNifMapIterator iter;
enif_map_iterator_create(env, my_map, &iter, ERL_NIF_MAP_ITERATOR_FIRST);
while (enif_map_iterator_get_pair(env, &iter, &key, &value)) {
    do_something(key,value);
    enif_map_iterator_next(env, &iter);
}
enif_map_iterator_destroy(env, &iter);

Destroys a map iterator created by enif_map_iterator_create.

Gets key and value terms at the current map iterator position.

On success, sets *key and *value and returns true. Returns false if the iterator is positioned at head (before first entry) or tail (beyond last entry).

Returns true if map iterator iter is positioned before the first entry.

Returns true if map iterator iter is positioned after the last entry.

Increments map iterator to point to the next key-value entry.

Returns true if the iterator is now positioned at a valid key-value entry, or false if the iterator is positioned at the tail (beyond the last entry).

Decrements map iterator to point to the previous key-value entry.

Returns true if the iterator is now positioned at a valid key-value entry, or false if the iterator is positioned at the head (before the first entry).

Starts monitoring a process from a resource. When a process is monitored, a process exit results in a call to the provided down callback associated with the resource type.

Argument obj is pointer to the resource to hold the monitor and *target_pid identifies the local process to be monitored.

If mon is not NULL, a successful call stores the identity of the monitor in the ErlNifMonitor struct pointed to by mon. This identifier is used to refer to the monitor for later removal with enif_demonitor_process or compare with enif_compare_monitors. A monitor is automatically removed when it triggers or when the resource is deallocated.

Argument caller_env is the environment of the calling process or callback. Must only be NULL if calling from a custom thread.

Returns 0 on success, < 0 if no down callback is provided, and > 0 if the process is no longer alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Returns the current Erlang monotonic time. Notice that it is not uncommon with negative values.

time_unit is the time unit of the returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument, or if called from a thread that is not a scheduler thread.

See also ErlNifTime and ErlNifTimeUnit.

Same as erl_drv_mutex_create.

Same as erl_drv_mutex_destroy.

Same as erl_drv_mutex_lock.

Same as erl_drv_mutex_name.

Same as erl_drv_mutex_trylock.

Same as erl_drv_mutex_unlock.

Returns an erlang:now() time stamp.

This function is deprecated.

Creates or takes over a resource type identified by the string name and gives it the destructor function pointed to by dtor. Argument flags can have the following values:

The two flag values can be combined with bitwise OR. The resource type name is local to the calling module. Argument module_str is not (yet) used and must be NULL. dtor can be NULL if no destructor is needed.

On success, the function returns a pointer to the resource type and *tried is set to either ERL_NIF_RT_CREATE or ERL_NIF_RT_TAKEOVER to indicate what was done. On failure, returns NULL and sets *tried to flags. It is allowed to set tried to NULL.

Notice that enif_open_resource_type is only allowed to be called in the two callbacks load and upgrade.

See also enif_open_resource_type_x.

Same as enif_open_resource_type except it accepts additional callback functions for resource types that are used together with enif_select and enif_monitor_process.

Argument init is a pointer to an ErlNifResourceTypeInit structure that contains the function pointers for destructor, down and stop callbacks for the resource type.

Works as erlang:port_command/2, except that it is always completely asynchronous.

Using a msg_env of NULL is an optimization, which groups together calls to enif_alloc_env, enif_make_copy, enif_port_command, and enif_free_env into one call. This optimization is only useful when a majority of the terms are to be copied from env to msg_env.

Returns true if the command is successfully sent. Returns false if the command fails, for example:

See also enif_get_local_port.

Returns the pointer to the private data that was set by load or upgrade.

Creates an error exception with the term reason to be returned from a NIF, and associates it with environment env. Once a NIF or any function it calls invokes enif_raise_exception, the runtime ensures that the exception it creates is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.

The return value from enif_raise_exception can only be used as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception, but not to any other NIF API function.

See also enif_has_pending_exception and enif_make_badarg.

Reallocates memory allocated by enif_alloc to size bytes.

Returns NULL if the reallocation fails.

The returned pointer is suitably aligned for any built-in type that fit in the allocated memory.

Changes the size of a binary bin. The source binary can be read-only, in which case it is left untouched and a mutable copy is allocated and assigned to *bin.

Returns true on success, or false if memory allocation failed.

Releases a binary obtained from enif_alloc_binary.

Removes a reference to resource object obj obtained from enif_alloc_resource. The resource object is destructed when the last reference is removed. Each call to enif_release_resource must correspond to a previous call to enif_alloc_resource or enif_keep_resource. References made by enif_make_resource can only be removed by the garbage collector.

Same as erl_drv_rwlock_create.

Same as erl_drv_rwlock_destroy.

Same as erl_drv_rwlock_name.

Same as erl_drv_rwlock_rlock.

Same as erl_drv_rwlock_runlock.

Same as erl_drv_rwlock_rwlock.

Same as erl_drv_rwlock_rwunlock.

Same as erl_drv_rwlock_tryrlock.

Same as erl_drv_rwlock_tryrwlock.

Schedules NIF fp to execute. This function allows an application to break up long-running work into multiple regular NIF calls or to schedule a dirty NIF to execute on a dirty scheduler thread.

The calling NIF must use the return value of enif_schedule_nif as its own return value.

Be aware that enif_schedule_nif, as its name implies, only schedules the NIF for future execution. The calling NIF does not block waiting for the scheduled NIF to execute and return. This means that the calling NIF cannot expect to receive the scheduled NIF return value and use it for further operations.

This function can be used to receive asynchronous notifications when OS-specific event objects become ready for either read or write operations.

Argument event identifies the event object. On Unix systems, the functions select/poll are used. The event object must be a socket, pipe or other file descriptor object that select/poll can use.

Argument mode describes the type of events to wait for. It can be ERL_NIF_SELECT_READ, ERL_NIF_SELECT_WRITE or a bitwise OR combination to wait for both. It can also be ERL_NIF_SELECT_STOP which is described further below. When a read or write event is triggered, a notification message like this is sent to the process identified by pid:

{select, Obj, Ref, ready_input | ready_output}

ready_input or ready_output indicates if the event object is ready for reading or writing.

Argument pid may be NULL to indicate the calling process.

Argument obj is a resource object obtained from enif_alloc_resource. The purpose of the resource objects is as a container of the event object to manage its state and lifetime. A handle to the resource is received in the notification message as Obj.

Argument ref must be either a reference obtained from erlang:make_ref/0 or the atom undefined. It will be passed as Ref in the notifications. If a selective receive statement is used to wait for the notification then a reference created just before the receive will exploit a runtime optimization that bypasses all earlier received messages in the queue.

The notifications are one-shot only. To receive further notifications of the same type (read or write), repeated calls to enif_select must be made after receiving each notification.

Use ERL_NIF_SELECT_STOP as mode in order to safely close an event object that has been passed to enif_select. The stop callback of the resource obj will be called when it is safe to close the event object. This safe way of closing event objects must be used even if all notifications have been received and no further calls to enif_select have been made.

The first call to enif_select for a specific OS event will establish a relation between the event object and the containing resource. All subsequent calls for an event must pass its containing resource as argument obj. The relation is dissolved when enif_select has been called with mode as ERL_NIF_SELECT_STOP and the corresponding stop callback has returned. A resource can contain several event objects but one event object can only be contained within one resource. A resource will not be destructed until all its contained relations have been dissolved.

Returns a non-negative value on success where the following bits can be set:

Returns a negative value if the call failed where the following bits can be set:

Example:

retval = enif_select(env, fd, ERL_NIF_SELECT_STOP, resource, ref);
if (retval < 0) {
    /* handle error */
}
/* Success! */
if (retval & ERL_NIF_SELECT_STOP_CALLED) {
    /* ... */
}

Initializes the ErlNifPid variable at *pid to represent the calling process.

Returns pid if successful, or NULL if caller_env is not a process bound environment.

Sends a message to a process.

Returns true if the message is successfully sent. Returns false if the send operation fails, that is:

The message environment msg_env with all its terms (including msg) is invalidated by a successful call to enif_send. The environment is to either be freed with enif_free_env of cleared for reuse with enif_clear_env.

If msg_env is set to NULL, the msg term is copied and the original term and its environment is still valid after the call.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Gets the byte size of resource object obj obtained by enif_alloc_resource.

Similar to snprintf but this format string also accepts "%T", which formats Erlang terms of type ERL_NIF_TERM.

This function is primarily intended for debugging purpose. It is not recommended to print very large terms with %T. The function may change errno, even if successful.

Same as driver_system_info.

Allocates a new binary with enif_alloc_binary and stores the result of encoding term according to the Erlang external term format.

Returns true on success, or false if the allocation fails.

See also erlang:term_to_binary/1 and enif_binary_to_term.

Same as erl_drv_thread_create.

Same as erl_drv_thread_exit.

Same as erl_drv_thread_join.

Same as erl_drv_thread_name.

Same as erl_drv_thread_opts_create.

Same as erl_drv_thread_opts_destroy.

Same as erl_drv_thread_self.

Determine the type of currently executing thread. A positive value indicates a scheduler thread while a negative value or zero indicates another type of thread. Currently the following specific types exist (which may be extended in the future):

Returns the current time offset between Erlang monotonic time and Erlang system time converted into the time_unit passed as argument.

time_unit is the time unit of the returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument or if called from a thread that is not a scheduler thread.

See also ErlNifTime and ErlNifTimeUnit.

Same as erl_drv_tsd_get.

Same as erl_drv_tsd_key_create.

Same as erl_drv_tsd_key_destroy.

Same as erl_drv_tsd_set.

Equivalent to enif_fprintf except that its called with a va_list instead of a variable number of arguments.

Equivalent to enif_snprintf except that its called with a va_list instead of a variable number of arguments.

Looks up a process by its registered name.

On success, sets *pid to the local process registered with name and returns true. If name is not a registered process, or is not an atom, false is returned and *pid is unchanged.

Works as erlang:whereis/1, but restricted to processes. See enif_whereis_port to resolve registered ports.

Looks up a port by its registered name.

On success, sets *port to the port registered with name and returns true. If name is not a registered port, or is not an atom, false is returned and *port is unchanged.

Works as erlang:whereis/1, but restricted to ports. See enif_whereis_pid to resolve registered processes.