erl_driver

void add_driver_entry( ErlDrvEntry *de)

Adds a driver entry to the list of drivers known by Erlang. The init function of parameter de is called.

void * driver_alloc( ErlDrvSizeT size)

Allocates a memory block of the size specified in size, and returns it. This fails only on out of memory, in which case NULL is returned. (This is most often a wrapper for malloc).

Memory allocated must be explicitly freed with a corresponding call to driver_free (unless otherwise stated).

This function is thread-safe.

ErlDrvBinary * driver_alloc_binary( ErlDrvSizeT size)

Allocates a driver binary with a memory block of at least size bytes, and returns a pointer to it, or NULL on failure (out of memory). When a driver binary has been sent to the emulator, it must not be changed. Every allocated binary is to be freed by a corresponding call to driver_free_binary (unless otherwise stated).

Notice that a driver binary has an internal reference counter. This means that calling driver_free_binary, it may not actually dispose of it. If it is sent to the emulator, it can be referenced there.

The driver binary has a field, orig_bytes, which marks the start of the data in the binary.

This function is thread-safe.

long driver_async( ErlDrvPort port, unsigned int* key, void (*async_invoke)(void*), void* async_data, void (*async_free)(void*))

Performs an asynchronous call. The function async_invoke is invoked in a thread separate from the emulator thread. This enables the driver to perform time-consuming, blocking operations without blocking the emulator.

The async thread pool size can be set with command-line argument +A in erl(1). If an async thread pool is unavailable, the call is made synchronously in the thread calling driver_async. The current number of async threads in the async thread pool can be retrieved through driver_system_info.

If a thread pool is available, a thread is used. If argument key is NULL, the threads from the pool are used in a round-robin way, each call to driver_async uses the next thread in the pool. With argument key set, this behavior is changed. The two same values of *key always get the same thread.

To ensure that a driver instance always uses the same thread, the following call can be used:

unsigned int myKey = driver_async_port_key(myPort);

r = driver_async(myPort, &myKey, myData, myFunc);    

It is enough to initialize myKey once for each driver instance.

If a thread is already working, the calls are queued up and executed in order. Using the same thread for each driver instance ensures that the calls are made in sequence.

The async_data is the argument to the functions async_invoke and async_free. It is typically a pointer to a structure containing a pipe or event that can be used to signal that the async operation completed. The data is to be freed in async_free.

When the async operation is done, ready_async driver entry function is called. If ready_async is NULL in the driver entry, the async_free function is called instead.

The return value is -1 if the driver_async call fails.

unsigned int driver_async_port_key( ErlDrvPort port)

OTP R16B02

Calculates a key for later use in driver_async. The keys are evenly distributed so that a fair mapping between port IDs and async thread IDs is achieved.

long driver_binary_dec_refc( ErlDrvBinary *bin)

Decrements the reference count on bin and returns the reference count reached after the decrement.

This function is thread-safe.

long driver_binary_get_refc( ErlDrvBinary *bin)

Returns the current reference count on bin.

This function is thread-safe.

long driver_binary_inc_refc( ErlDrvBinary *bin)

Increments the reference count on bin and returns the reference count reached after the increment.

This function is thread-safe.

ErlDrvTermData driver_caller( ErlDrvPort port)

Returns the process ID of the process that made the current call to the driver. The process ID can be used with driver_send_term to send back data to the caller. driver_caller only returns valid data when currently executing in one of the following driver callbacks:

start

Called from erlang:open_port/2.

output

Called from erlang:send/2 and erlang:port_command/2.

outputv

Called from erlang:send/2 and erlang:port_command/2.

control

Called from erlang:port_control/3.

call

Called from erlang:port_call/3.

Notice that this function is not thread-safe, not even when the emulator with SMP support is used.

int driver_cancel_timer( ErlDrvPort port)

Cancels a timer set with driver_set_timer.

The return value is 0.

int driver_compare_monitors( const ErlDrvMonitor *monitor1, const ErlDrvMonitor *monitor2)

Compares two ErlDrvMonitors. 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.

ErlDrvTermData driver_connected( ErlDrvPort port)

Returns the port owner process.

Notice that this function is not thread-safe, not even when the emulator with SMP support is used.

ErlDrvPort driver_create_port( ErlDrvPort port, ErlDrvTermData owner_pid, char* name, ErlDrvData drv_data)

Creates a new port executing the same driver code as the port creating the new port.

port

The port handle of the port (driver instance) creating the new port.

owner_pid

The process ID of the Erlang process to become owner of the new port. This process will be linked to the new port. You usually want to use driver_caller(port) as owner_pid.

name

The port name of the new port. You usually want to use the same port name as the driver name (driver_name field of the driver_entry).

drv_data

The driver-defined handle that is passed in later calls to driver callbacks. Notice that the driver start callback is not called for this new driver instance. The driver-defined handle is normally created in the driver start callback when a port is created through erlang:open_port/2.

The caller of driver_create_port is allowed to manipulate the newly created port when driver_create_port has returned. When port level locking is used, the creating port is only allowed to manipulate the newly created port until the current driver callback, which was called by the emulator, returns.

int driver_demonitor_process( ErlDrvPort port, const ErlDrvMonitor *monitor)

Cancels a monitor created earlier.

Returns 0 if a monitor was removed and > 0 if the monitor no longer exists.

ErlDrvSizeT driver_deq( ErlDrvPort port, ErlDrvSizeT size)

Dequeues data by moving the head pointer forward in the driver queue by size bytes. The data in the queue is deallocated.

Returns the number of bytes remaining in the queue on success, otherwise -1.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

int driver_enq( ErlDrvPort port, char* buf, ErlDrvSizeT len)

Enqueues data in the driver queue. The data in buf is copied (len bytes) and placed at the end of the driver queue. The driver queue is normally used in a FIFO way.

The driver queue is available to queue output from the emulator to the driver (data from the driver to the emulator is queued by the emulator in normal Erlang message queues). This can be useful if the driver must wait for slow devices, and so on, and wants to yield back to the emulator. The driver queue is implemented as an ErlIOVec.

When the queue contains data, the driver does not close until the queue is empty.

The return value is 0.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

int driver_enq_bin( ErlDrvPort port, ErlDrvBinary *bin, ErlDrvSizeT offset, ErlDrvSizeT len)

Enqueues a driver binary in the driver queue. The data in bin at offset with length len is placed at the end of the queue. This function is most often faster than driver_enq, because no data must be copied.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

The return value is 0.

int driver_enqv( ErlDrvPort port, ErlIOVec *ev, ErlDrvSizeT skip)

Enqueues the data in ev, skipping the first skip bytes of it, at the end of the driver queue. It is faster than driver_enq, because no data must be copied.

The return value is 0.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

int driver_failure( ErlDrvPort port, int error)

int driver_failure_atom( ErlDrvPort port, char *string)

int driver_failure_posix( ErlDrvPort port, int error)

Signals to Erlang that the driver has encountered an error and is to be closed. The port is closed and the tuple {'EXIT', error, Err} is sent to the port owner process, where error is an error atom (driver_failure_atom and driver_failure_posix) or an integer (driver_failure).

The driver is to fail only when in severe error situations, when the driver cannot possibly keep open, for example, buffer allocation gets out of memory. For normal errors it is more appropriate to send error codes with driver_output.

The return value is 0.

int driver_failure_eof( ErlDrvPort port)

Signals to Erlang that the driver has encountered an EOF and is to be closed, unless the port was opened with option eof, in which case eof is sent to the port. Otherwise the port is closed and an 'EXIT' message is sent to the port owner process.

The return value is 0.

void driver_free( void *ptr)

Frees the memory pointed to by ptr. The memory is to have been allocated with driver_alloc. All allocated memory is to be deallocated, only once. There is no garbage collection in drivers.

This function is thread-safe.

void driver_free_binary( ErlDrvBinary *bin)

Frees a driver binary bin, allocated previously with driver_alloc_binary. As binaries in Erlang are reference counted, the binary can still be around.

This function is thread-safe.

ErlDrvTermData driver_get_monitored_process( ErlDrvPort port, const ErlDrvMonitor *monitor)

Returns the process ID associated with a living monitor. It can be used in the process_exit callback to get the process identification for the exiting process.

Returns driver_term_nil if the monitor no longer exists.

int driver_get_now( ErlDrvNowData *now)

Reads a time stamp into the memory pointed to by parameter now. For information about specific fields, see ErlDrvNowData.

The return value is 0, unless the now pointer is invalid, in which case it is < 0.

int driver_lock_driver( ErlDrvPort port)

Locks the driver used by the port port in memory for the rest of the emulator process' lifetime. After this call, the driver behaves as one of Erlang's statically linked-in drivers.

ErlDrvTermData driver_mk_atom( char* string)

Returns an atom given a name string. The atom is created and does not change, so the return value can be saved and reused, which is faster than looking up the atom several times.

Notice that this function is not thread-safe, not even when the emulator with SMP support is used.

ErlDrvTermData driver_mk_port( ErlDrvPort port)

Converts a port handle to the Erlang term format, usable in erl_drv_output_term and erl_drv_send_term.

Notice that this function is not thread-safe, not even when the emulator with SMP support is used.

int driver_monitor_process( ErlDrvPort port, ErlDrvTermData process, ErlDrvMonitor *monitor)

Starts monitoring a process from a driver. When a process is monitored, a process exit results in a call to the provided process_exit callback in the ErlDrvEntry structure. The ErlDrvMonitor structure is filled in, for later removal or compare.

Parameter process is to be the return value of an earlier call to driver_caller or driver_connected call.

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

int driver_output( ErlDrvPort port, char *buf, ErlDrvSizeT len)

Sends data from the driver up to the emulator. The data is received as terms or binary data, depending on how the driver port was opened.

The data is queued in the port owner process' message queue. Notice that this does not yield to the emulator (as the driver and the emulator run in the same thread).

Parameter buf points to the data to send, and len is the number of bytes.

The return value for all output functions is 0 for normal use. If the driver is used for distribution, it can fail and return -1.

int driver_output_binary( ErlDrvPort port, char *hbuf, ErlDrvSizeT hlen, ErlDrvBinary* bin, ErlDrvSizeT offset, ErlDrvSizeT len)

Sends data to a port owner process from a driver binary. It has a header buffer (hbuf and hlen) just like driver_output2. Parameter hbuf can be NULL.

Parameter offset is an offset into the binary and len is the number of bytes to send.

Driver binaries are created with driver_alloc_binary.

The data in the header is sent as a list and the binary as an Erlang binary in the tail of the list.

For example, if hlen is 2, the port owner process receives [H1, H2 | <<T>>].

The return value is 0 for normal use.

Notice that, using the binary syntax in Erlang, the driver application can match the header directly from the binary, so the header can be put in the binary, and hlen can be set to 0.

int driver_output_term( ErlDrvPort port, ErlDrvTermData* term, int n)

Parameters term and n work as in erl_drv_output_term.

Notice that this function is not thread-safe, not even when the emulator with SMP support is used.

int driver_output2( ErlDrvPort port, char *hbuf, ErlDrvSizeT hlen, char *buf, ErlDrvSizeT len)

First sends hbuf (length in hlen) data as a list, regardless of port settings. Then sends buf as a binary or list. For example, if hlen is 3, the port owner process receives [H1, H2, H3 | T].

The point of sending data as a list header, is to facilitate matching on the data received.

The return value is 0 for normal use.

int driver_outputv( ErlDrvPort port, char* hbuf, ErlDrvSizeT hlen, ErlIOVec *ev, ErlDrvSizeT skip)

Sends data from an I/O vector, ev, to the port owner process. It has a header buffer (hbuf and hlen), just like driver_output2.

Parameter skip is a number of bytes to skip of the ev vector from the head.

You get vectors of ErlIOVec type from the driver queue (see below), and the outputv driver entry function. You can also make them yourself, if you want to send several ErlDrvBinary buffers at once. Often it is faster to use driver_output or .

For example, if hlen is 2 and ev points to an array of three binaries, the port owner process receives [H1, H2, <<B1>>, <<B2>> | <<B3>>].

The return value is 0 for normal use.

The comment for driver_output_binary also applies for driver_outputv.

ErlDrvPDL driver_pdl_create( ErlDrvPort port)

Creates a port data lock associated with the port.

Returns a newly created port data lock on success, otherwise NULL. The function fails if port is invalid or if a port data lock already has been associated with the port.

long driver_pdl_dec_refc( ErlDrvPDL pdl)

Decrements the reference count of the port data lock passed as argument (pdl).

The current reference count after the decrement has been performed is returned.

This function is thread-safe.

long driver_pdl_get_refc( ErlDrvPDL pdl)

Returns the current reference count of the port data lock passed as argument (pdl).

This function is thread-safe.

long driver_pdl_inc_refc( ErlDrvPDL pdl)

Increments the reference count of the port data lock passed as argument (pdl).

The current reference count after the increment has been performed is returned.

This function is thread-safe.

void driver_pdl_lock( ErlDrvPDL pdl)

Locks the port data lock passed as argument (pdl).

This function is thread-safe.

void driver_pdl_unlock( ErlDrvPDL pdl)

Unlocks the port data lock passed as argument (pdl).

This function is thread-safe.

SysIOVec *driver_peekq( ErlDrvPort port, int *vlen)

Retrieves the driver queue as a pointer to an array of SysIOVecs. It also returns the number of elements in vlen. This is one of two ways to get data out of the queue.

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

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

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

ErlDrvSizeT driver_peekqv( ErlDrvPort port, ErlIOVec *ev)

OTP R15B

Retrieves the driver queue into a supplied ErlIOVec ev. It also returns the queue size. This is one of two ways to get data out of the queue.

If ev is NULL, all ones that is -1 type cast to ErlDrvSizeT are returned.

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

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

int driver_pushq( ErlDrvPort port, char* buf, ErlDrvSizeT len)

Puts data at the head of the driver queue. The data in buf is copied (len bytes) and placed at the beginning of the queue.

The return value is 0.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

int driver_pushq_bin( ErlDrvPort port, ErlDrvBinary *bin, ErlDrvSizeT offset, ErlDrvSizeT len)

Puts data in the binary bin, at offset with length len at the head of the driver queue. It is most often faster than driver_pushq, because no data must be copied.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

The return value is 0.

int driver_pushqv( ErlDrvPort port, ErlIOVec *ev, ErlDrvSizeT skip)

Puts the data in ev, skipping the first skip bytes of it, at the head of the driver queue. It is faster than driver_pushq, because no data must be copied.

The return value is 0.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

int driver_read_timer( ErlDrvPort port, unsigned long *time_left)

Reads the current time of a timer, and places the result in time_left. This is the time in milliseconds, before the time-out occurs.

The return value is 0.

void * driver_realloc( void *ptr, ErlDrvSizeT size)

Resizes a memory block, either in place, or by allocating a new block, copying the data, and freeing the old block. A pointer is returned to the reallocated memory. On failure (out of memory), NULL is returned. (This is most often a wrapper for realloc.)

This function is thread-safe.

ErlDrvBinary * driver_realloc_binary( ErlDrvBinary *bin, ErlDrvSizeT size)

Resizes a driver binary, while keeping the data.

Returns the resized driver binary on success. Returns NULL on failure (out of memory).

This function is thread-safe.

int driver_select( ErlDrvPort port, ErlDrvEvent event, int mode, int on)

This function is used by drivers to provide the emulator with events to check for. This enables the emulator to call the driver when something has occurred asynchronously.

Parameter event identifies an OS-specific event object. On Unix systems, the functions select/poll are used. The event object must be a socket or pipe (or other object that select/poll can use). On Windows, the Win32 API function WaitForMultipleObjects is used. This places other restrictions on the event object; see the Win32 SDK documentation.

Parameter on is to be 1 for setting events and 0 for clearing them.

Parameter mode is a bitwise OR combination of ERL_DRV_READ, ERL_DRV_WRITE, and ERL_DRV_USE. The first two specify whether to wait for read events and/or write events. A fired read event calls ready_input and a fired write event calls ready_output.

ERL_DRV_USE specifies if we are using the event object or if we want to close it. On an emulator with SMP support, it is not safe to clear all events and then close the event object after driver_select has returned. Another thread can still be using the event object internally. To safely close an event object, call driver_select with ERL_DRV_USE and on==0, which clears all events and then either calls stop_select or schedules it to be called when it is safe to close the event object. ERL_DRV_USE is to be set together with the first event for an event object. It is harmless to set ERL_DRV_USE even if it already has been done. Clearing all events but keeping ERL_DRV_USE set indicates that we are using the event object and probably will set events for it again.

The return value is 0, unless ready_input/ready_output is NULL, in which case it is -1.

int driver_send_term( ErlDrvPort port, ErlDrvTermData receiver, ErlDrvTermData* term, int n)

Parameters term and n work as in erl_drv_output_term.

This function is only thread-safe when the emulator with SMP support is used.

int driver_set_timer( ErlDrvPort port, unsigned long time)

Sets a timer on the driver, which will count down and call the driver when it is timed out. Parameter time is the time in milliseconds before the timer expires.

When the timer reaches 0 and expires, the driver entry function timeout is called.

Notice that only one timer exists on each driver instance; setting a new timer replaces an older one.

Return value is 0, unless the timeout driver function is NULL, in which case it is -1.

ErlDrvSizeT driver_sizeq( ErlDrvPort port)

Returns the number of bytes currently in the driver queue.

This function can be called from any thread if a port data lock associated with the port is locked by the calling thread during the call.

void driver_system_info( ErlDrvSysInfo *sys_info_ptr, size_t size)

Writes information about the Erlang runtime system into the ErlDrvSysInfo structure referred to by the first argument. The second argument is to be the size of the ErlDrvSysInfo structure, that is, sizeof(ErlDrvSysInfo).

For information about specific fields, see ErlDrvSysInfo.

ErlDrvSizeT driver_vec_to_buf( ErlIOVec *ev, char *buf, ErlDrvSizeT len)

Collects several segments of data, referenced by ev, by copying them in order to the buffer buf, of the size len.

If the data is to be sent from the driver to the port owner process, it is faster to use driver_outputv.

The return value is the space left in the buffer, that is, if ev contains less than len bytes it is the difference, and if ev contains len bytes or more, it is 0. This is faster if there is more than one header byte, as the binary syntax can construct integers directly from the binary.

void erl_drv_busy_msgq_limits( ErlDrvPort port, ErlDrvSizeT *low, ErlDrvSizeT *high)

OTP R16B

Sets and gets limits that will be used for controlling the busy state of the port message queue.

The port message queue is set into a busy state when the amount of command data queued on the message queue reaches the high limit. The port message queue is set into a not busy state when the amount of command data queued on the message queue falls below the low limit. Command data is in this context data passed to the port using either Port ! {Owner, {command, Data}} or port_command/[2,3]. Notice that these limits only concerns command data that have not yet reached the port. The busy port feature can be used for data that has reached the port.

Valid limits are values in the range [ERL_DRV_BUSY_MSGQ_LIM_MIN, ERL_DRV_BUSY_MSGQ_LIM_MAX]. Limits are automatically adjusted to be sane. That is, the system adjusts values so that the low limit used is lower than or equal to the high limit used. By default the high limit is 8 kB and the low limit is 4 kB.

By passing a pointer to an integer variable containing the value ERL_DRV_BUSY_MSGQ_READ_ONLY, the currently used limit is read and written back to the integer variable. A new limit can be set by passing a pointer to an integer variable containing a valid limit. The passed value is written to the internal limit. The internal limit is then adjusted. After this the adjusted limit is written back to the integer variable from which the new value was read. Values are in bytes.

The busy message queue feature can be disabled either by setting the ERL_DRV_FLAG_NO_BUSY_MSGQ driver flag in the driver_entry used by the driver, or by calling this function with ERL_DRV_BUSY_MSGQ_DISABLED as a limit (either low or high). When this feature has been disabled, it cannot be enabled again. When reading the limits, both are ERL_DRV_BUSY_MSGQ_DISABLED if this feature has been disabled.

Processes sending command data to the port are suspended if either the port is busy or if the port message queue is busy. Suspended processes are resumed when neither the port or the port message queue is busy.

For information about busy port functionality, see set_busy_port.

void erl_drv_cond_broadcast( ErlDrvCond *cnd)

Broadcasts on a condition variable. That is, if other threads are waiting on the condition variable being broadcast on, all of them are woken.

cnd is a pointer to a condition variable to broadcast on.

This function is thread-safe.

ErlDrvCond *erl_drv_cond_create( char *name)

Creates a condition variable and returns a pointer to it.

name is a string identifying the created condition variable. It is used to identify the condition variable in planned future debug functionality.

Returns NULL on failure. The driver creating the condition variable is responsible for destroying it before the driver is unloaded.

This function is thread-safe.

void erl_drv_cond_destroy( ErlDrvCond *cnd)

Destroys a condition variable previously created by erl_drv_cond_create.

cnd is a pointer to a condition variable to destroy.

This function is thread-safe.

char *erl_drv_cond_name( ErlDrvCond *cnd)

OTP R16B02

Returns a pointer to the name of the condition.

cnd is a pointer to an initialized condition.

void erl_drv_cond_signal( ErlDrvCond *cnd)

Signals on a condition variable. That is, if other threads are waiting on the condition variable being signaled, one of them is woken.

cnd is a pointer to a condition variable to signal on.

This function is thread-safe.

void erl_drv_cond_wait( ErlDrvCond *cnd, ErlDrvMutex *mtx)

Waits on a condition variable. The calling thread is blocked until another thread wakes it by signaling or broadcasting on the condition variable. Before the calling thread is blocked, it unlocks the mutex passed as argument. When the calling thread is woken, it locks the same mutex before returning. That is, the mutex currently must be locked by the calling thread when calling this function.

cnd is a pointer to a condition variable to wait on. mtx is a pointer to a mutex to unlock while waiting.

This function is thread-safe.

int erl_drv_consume_timeslice( ErlDrvPort port, int percent)

OTP R16B

Gives the runtime system a hint about how much CPU time the current driver callback call has consumed since the last hint, or since the the start of the callback if no previous hint has been given.

port

Port handle of the executing port.

percent

Approximate consumed fraction of a full time-slice in percent.

The time is specified as a fraction, in percent, of a full time-slice that a port is allowed to execute before it is to surrender the CPU to other runnable ports or processes. Valid range is [1, 100]. The scheduling time-slice 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 the consumed fraction of the time-slice. Lengthy driver callbacks should, regardless of this, frequently call this function to determine if it is allowed to continue execution or not.

This function returns a non-zero value if the time-slice has been exhausted, and zero if the callback is allowed to continue execution. If a non-zero value is returned, the driver callback is to return as soon as possible in order for the port to be able to yield.

This function is provided to better support co-operative scheduling, improve system responsiveness, and to make it easier to prevent misbehaviors of the VM because of a port monopolizing a scheduler thread. It can be used when dividing lengthy work into some repeated driver callback calls, without the need to use threads.

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

ErlDrvTime erl_drv_convert_time_unit( ErlDrvTime val, ErlDrvTimeUnit from, ErlDrvTimeUnit to)

OTP 18.3

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

val

Value to convert time unit for.

from

Time unit of val.

to

Time unit of returned value.

Returns ERL_DRV_TIME_ERROR if called with an invalid time unit argument.

See also ErlDrvTime and ErlDrvTimeUnit.

int erl_drv_equal_tids( ErlDrvTid tid1, ErlDrvTid tid2)

Compares two thread identifiers, tid1 and tid2, for equality.

Returns 0 it they are not equal, and a value not equal to 0 if they are equal.

This function is thread-safe.

int erl_drv_getenv( const char *key, char *value, size_t *value_size)

Retrieves the value of an environment variable.

key

A NULL-terminated string containing the name of the environment variable.

value

A pointer to an output buffer.

value_size

A pointer to an integer. The integer is used both for passing input and output sizes (see below).

When this function is called, *value_size is to contain the size of the value buffer.

On success, 0 is returned, the value of the environment variable has been written to the value buffer, and *value_size contains the string length (excluding the terminating NULL character) of the value written to the value buffer.

On failure, that is, no such environment variable was found, a value < 0 is returned. When the size of the value buffer is too small, a value > 0 is returned and *value_size has been set to the buffer size needed.

This function is thread-safe.

void erl_drv_init_ack( ErlDrvPort port, ErlDrvData res)

OTP 19.0

Acknowledges the start of the port.

port

The port handle of the port (driver instance) doing the acknowledgment.

res

The result of the port initialization. Can be the same values as the return value of start, that is, any of the error codes or the ErlDrvData that is to be used for this port.

When this function is called the initiating erlang:open_port call is returned as if the start function had just been called. It can only be used when flag ERL_DRV_FLAG_USE_INIT_ACK has been set on the linked-in driver.

ErlDrvTime erl_drv_monotonic_time( ErlDrvTimeUnit time_unit)

OTP 18.3

Returns Erlang monotonic time. Notice that negative values are not uncommon.

time_unit is time unit of returned value.

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

See also ErlDrvTime and ErlDrvTimeUnit.

ErlDrvMutex *erl_drv_mutex_create( char *name)

Creates a mutex and returns a pointer to it.

name is a string identifying the created mutex. It is used to identify the mutex in debug functionality (see note).

Returns NULL on failure. The driver creating the mutex is responsible for destroying it before the driver is unloaded.

This function is thread-safe.

void erl_drv_mutex_destroy( ErlDrvMutex *mtx)

Destroys a mutex previously created by erl_drv_mutex_create. The mutex must be in an unlocked state before it is destroyed.

mtx is a pointer to a mutex to destroy.

This function is thread-safe.

void erl_drv_mutex_lock( ErlDrvMutex *mtx)

Locks a mutex. The calling thread is blocked until the mutex has been locked. A thread that has currently locked the mutex cannot lock the same mutex again.

mtx is a pointer to a mutex to lock.

This function is thread-safe.

char *erl_drv_mutex_name( ErlDrvMutex *mtx)

OTP R16B02

Returns a pointer to the mutex name.

mtx is a pointer to an initialized mutex.

int erl_drv_mutex_trylock( ErlDrvMutex *mtx)

Tries to lock a mutex. A thread that has currently locked the mutex cannot try to lock the same mutex again.

mtx is a pointer to a mutex to try to lock.

Returns 0 on success, otherwise EBUSY.

This function is thread-safe.

void erl_drv_mutex_unlock( ErlDrvMutex *mtx)

Unlocks a mutex. The mutex currently must be locked by the calling thread.

mtx is a pointer to a mutex to unlock.

This function is thread-safe.

int erl_drv_output_term( ErlDrvTermData port, ErlDrvTermData* term, int n)

OTP R16B

Sends data in the special driver term format to the port owner process. This is a fast way to deliver term data from a driver. It needs no binary conversion, so the port owner process receives data as normal Erlang terms. The erl_drv_send_term functions can be used for sending to any process on the local node.

Parameter term points to an array of ErlDrvTermData with n elements. This array contains terms described in the driver term format. Every term consists of 1-4 elements in the array. The first term has a term type and then arguments. Parameter port specifies the sending port.

Tuples, maps, and lists (except strings, see below) are built in reverse polish notation, so that to build a tuple, the elements are specified first, and then the tuple term, with a count. Likewise for lists and maps.

• A tuple must be specified with the number of elements. (The elements precede the ERL_DRV_TUPLE term.)

• A map must be specified with the number of key-value pairs N. The key-value pairs must precede the ERL_DRV_MAP in this order: key1,value1,key2,value2,...,keyN,valueN. Duplicate keys are not allowed.

• A list must be specified with the number of elements, including the tail, which is the last term preceding ERL_DRV_LIST.

The special term ERL_DRV_STRING_CONS is used to "splice" in a string in a list, a string specified this way is not a list in itself, but the elements are elements of the surrounding list.

Term type            Arguments
---------            ---------
ERL_DRV_NIL
ERL_DRV_ATOM         ErlDrvTermData atom (from driver_mk_atom(char *string))
ERL_DRV_INT          ErlDrvSInt integer
ERL_DRV_UINT         ErlDrvUInt integer
ERL_DRV_INT64        ErlDrvSInt64 *integer_ptr
ERL_DRV_UINT64       ErlDrvUInt64 *integer_ptr
ERL_DRV_PORT         ErlDrvTermData port (from driver_mk_port(ErlDrvPort port))
ERL_DRV_BINARY       ErlDrvBinary *bin, ErlDrvUInt len, ErlDrvUInt offset
ERL_DRV_BUF2BINARY   char *buf, ErlDrvUInt len
ERL_DRV_STRING       char *str, int len
ERL_DRV_TUPLE        int sz
ERL_DRV_LIST         int sz
ERL_DRV_PID          ErlDrvTermData pid (from driver_connected(ErlDrvPort port)
                     or driver_caller(ErlDrvPort port))
ERL_DRV_STRING_CONS  char *str, int len
ERL_DRV_FLOAT        double *dbl
ERL_DRV_EXT2TERM     char *buf, ErlDrvUInt len
ERL_DRV_MAP          int sz

The unsigned integer data type ErlDrvUInt and the signed integer data type ErlDrvSInt are 64 bits wide on a 64-bit runtime system and 32 bits wide on a 32-bit runtime system. They were introduced in ERTS 5.6 and replaced some of the int arguments in the list above.

The unsigned integer data type ErlDrvUInt64 and the signed integer data type ErlDrvSInt64 are always 64 bits wide. They were introduced in ERTS 5.7.4.

To build the tuple {tcp, Port, [100 | Binary]}, the following call can be made.

ErlDrvBinary* bin = ...
ErlDrvPort port = ...
ErlDrvTermData spec[] = {
    ERL_DRV_ATOM, driver_mk_atom("tcp"),
    ERL_DRV_PORT, driver_mk_port(drvport),
        ERL_DRV_INT, 100,
        ERL_DRV_BINARY, bin, 50, 0,
        ERL_DRV_LIST, 2,
    ERL_DRV_TUPLE, 3,
};
erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));    

Here bin is a driver binary of length at least 50 and drvport is a port handle. Notice that ERL_DRV_LIST comes after the elements of the list, likewise ERL_DRV_TUPLE.

The ERL_DRV_STRING_CONS term is a way to construct strings. It works differently from how ERL_DRV_STRING works. ERL_DRV_STRING_CONS builds a string list in reverse order (as opposed to how ERL_DRV_LIST works), concatenating the strings added to a list. The tail must be specified before ERL_DRV_STRING_CONS.

ERL_DRV_STRING constructs a string, and ends it. (So it is the same as ERL_DRV_NIL followed by ERL_DRV_STRING_CONS.)

/* to send [x, "abc", y] to the port: */
ErlDrvTermData spec[] = {
    ERL_DRV_ATOM, driver_mk_atom("x"),
    ERL_DRV_STRING, (ErlDrvTermData)"abc", 3,
    ERL_DRV_ATOM, driver_mk_atom("y"),
    ERL_DRV_NIL,
    ERL_DRV_LIST, 4
};
erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));    

/* to send "abc123" to the port: */
ErlDrvTermData spec[] = {
    ERL_DRV_NIL,        /* with STRING_CONS, the tail comes first */
    ERL_DRV_STRING_CONS, (ErlDrvTermData)"123", 3,
    ERL_DRV_STRING_CONS, (ErlDrvTermData)"abc", 3,
};
erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));    

The ERL_DRV_EXT2TERM term type is used for passing a term encoded with the external format, that is, a term that has been encoded by erlang:term_to_binary, erl_interface:ei(3), and so on. For example, if binp is a pointer to an ErlDrvBinary that contains term {17, 4711} encoded with the external format, and you want to wrap it in a two-tuple with the tag my_tag, that is, {my_tag, {17, 4711}}, you can do as follows:

ErlDrvTermData spec[] = {
        ERL_DRV_ATOM, driver_mk_atom("my_tag"),
        ERL_DRV_EXT2TERM, (ErlDrvTermData) binp->orig_bytes, binp->orig_size
    ERL_DRV_TUPLE, 2,
};
erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));    

To build the map #{key1 => 100, key2 => {200, 300}}, the following call can be made.

ErlDrvPort port = ...
ErlDrvTermData spec[] = {
    ERL_DRV_ATOM, driver_mk_atom("key1"),
        ERL_DRV_INT, 100,
    ERL_DRV_ATOM, driver_mk_atom("key2"),
        ERL_DRV_INT, 200,
        ERL_DRV_INT, 300,
    ERL_DRV_TUPLE, 2,
    ERL_DRV_MAP, 2
};
erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));    

If you want to pass a binary and do not already have the content of the binary in an ErlDrvBinary, you can benefit from using ERL_DRV_BUF2BINARY instead of creating an ErlDrvBinary through driver_alloc_binary and then pass the binary through ERL_DRV_BINARY. The runtime system often allocates binaries smarter if ERL_DRV_BUF2BINARY is used. However, if the content of the binary to pass already resides in an ErlDrvBinary, it is normally better to pass the binary using ERL_DRV_BINARY and the ErlDrvBinary in question.

The ERL_DRV_UINT, ERL_DRV_BUF2BINARY, and ERL_DRV_EXT2TERM term types were introduced in ERTS 5.6.

This function is only thread-safe when the emulator with SMP support is used.

int erl_drv_putenv( const char *key, char *value)

Sets the value of an environment variable.

key is a NULL-terminated string containing the name of the environment variable.

value is a NULL-terminated string containing the new value of the environment variable.

Returns 0 on success, otherwise a value != 0.

This function is thread-safe.

ErlDrvRWLock *erl_drv_rwlock_create( char *name)

Creates an rwlock and returns a pointer to it.

name is a string identifying the created rwlock. It is used to identify the rwlock in debug functionality (see note about the lock checker).

Returns NULL on failure. The driver creating the rwlock is responsible for destroying it before the driver is unloaded.

This function is thread-safe.

void erl_drv_rwlock_destroy( ErlDrvRWLock *rwlck)

Destroys an rwlock previously created by erl_drv_rwlock_create. The rwlock must be in an unlocked state before it is destroyed.

rwlck is a pointer to an rwlock to destroy.

This function is thread-safe.

char *erl_drv_rwlock_name( ErlDrvRWLock *rwlck)

OTP R16B02

Returns a pointer to the name of the rwlock.

rwlck is a pointer to an initialized rwlock.

void erl_drv_rwlock_rlock( ErlDrvRWLock *rwlck)

Read locks an rwlock. The calling thread is blocked until the rwlock has been read locked. A thread that currently has read or read/write locked the rwlock cannot lock the same rwlock again.

rwlck is a pointer to the rwlock to read lock.

This function is thread-safe.

void erl_drv_rwlock_runlock( ErlDrvRWLock *rwlck)

Read unlocks an rwlock. The rwlock currently must be read locked by the calling thread.

rwlck is a pointer to an rwlock to read unlock.

This function is thread-safe.

void erl_drv_rwlock_rwlock( ErlDrvRWLock *rwlck)

Read/write locks an rwlock. The calling thread is blocked until the rwlock has been read/write locked. A thread that currently has read or read/write locked the rwlock cannot lock the same rwlock again.

rwlck is a pointer to an rwlock to read/write lock.

This function is thread-safe.

void erl_drv_rwlock_rwunlock( ErlDrvRWLock *rwlck)

Read/write unlocks an rwlock. The rwlock currently must be read/write locked by the calling thread.

rwlck is a pointer to an rwlock to read/write unlock.

This function is thread-safe.

int erl_drv_rwlock_tryrlock( ErlDrvRWLock *rwlck)

Tries to read lock an rwlock.

rwlck is a pointer to an rwlock to try to read lock.

Returns 0 on success, otherwise EBUSY. A thread that currently has read or read/write locked the rwlock cannot try to lock the same rwlock again.

This function is thread-safe.

int erl_drv_rwlock_tryrwlock( ErlDrvRWLock *rwlck)

Tries to read/write lock an rwlock. A thread that currently has read or read/write locked the rwlock cannot try to lock the same rwlock again.

rwlckis pointer to an rwlock to try to read/write lock.

Returns 0 on success, otherwise EBUSY.

This function is thread-safe.

int erl_drv_send_term( ErlDrvTermData port, ErlDrvTermData receiver, ErlDrvTermData* term, int n)

OTP R16B

This function is the only way for a driver to send data to other processes than the port owner process. Parameter receiver specifies the process to receive the data.

Parameters port, term, and n work as in erl_drv_output_term.

This function is only thread-safe when the emulator with SMP support is used.

void erl_drv_set_os_pid( ErlDrvPort port, ErlDrvSInt pid)

OTP 19.0

Sets the os_pid seen when doing erlang:port_info/2 on this port.

port is the port handle of the port (driver instance) to set the pid on. pidis the pid to set.

int erl_drv_thread_create( char *name, ErlDrvTid *tid, void * (*func)(void *), void *arg, ErlDrvThreadOpts *opts)

Creates a new thread.

name

A string identifying the created thread. It is used to identify the thread in planned future debug functionality.

tid

A pointer to a thread identifier variable.

func

A pointer to a function to execute in the created thread.

arg

A pointer to argument to the func function.

opts

A pointer to thread options to use or NULL.

Returns 0 on success, otherwise an errno value is returned to indicate the error. The newly created thread begins executing in the function pointed to by func, and func is passed arg as argument. When erl_drv_thread_create returns, the thread identifier of the newly created thread is available in *tid. opts can be either a NULL pointer, or a pointer to an ErlDrvThreadOpts structure. If opts is a NULL pointer, default options are used, otherwise the passed options are used.

The created thread terminates either when func returns or if erl_drv_thread_exit is called by the thread. The exit value of the thread is either returned from func or passed as argument to erl_drv_thread_exit. The driver creating the thread is responsible for joining the thread, through erl_drv_thread_join, before the driver is unloaded. "Detached" threads cannot be created, that is, threads that do not need to be joined.

This function is thread-safe.

void erl_drv_thread_exit( void *exit_value)

Terminates the calling thread with the exit value passed as argument. exit_value is a pointer to an exit value or NULL.

You are only allowed to terminate threads created with erl_drv_thread_create.

The exit value can later be retrieved by another thread through erl_drv_thread_join.

This function is thread-safe.

int erl_drv_thread_join( ErlDrvTid tid, void **exit_value)

Joins the calling thread with another thread, that is, the calling thread is blocked until the thread identified by tid has terminated.

tid is the thread identifier of the thread to join. exit_value is a pointer to a pointer to an exit value, or NULL.

Returns 0 on success, otherwise an errno value is returned to indicate the error.

A thread can only be joined once. The behavior of joining more than once is undefined, an emulator crash is likely. If exit_value == NULL, the exit value of the terminated thread is ignored, otherwise the exit value of the terminated thread is stored at *exit_value.

This function is thread-safe.

char *erl_drv_thread_name( ErlDrvTid tid)

OTP R16B02

Returns a pointer to the name of the thread.

tid is a thread identifier.

ErlDrvThreadOpts * erl_drv_thread_opts_create( char *name)

Allocates and initializes a thread option structure.

name is a string identifying the created thread options. It is used to identify the thread options in planned future debug functionality.

Returns NULL on failure. A thread option structure is used for passing options to erl_drv_thread_create. If the structure is not modified before it is passed to erl_drv_thread_create, the default values are used.

This function is thread-safe.

void erl_drv_thread_opts_destroy( ErlDrvThreadOpts *opts)

Destroys thread options previously created by erl_drv_thread_opts_create.

opts is a pointer to thread options to destroy.

This function is thread-safe.

ErlDrvTid erl_drv_thread_self(void)

Returns the thread identifier of the calling thread.

This function is thread-safe.

ErlDrvTime erl_drv_time_offset( ErlDrvTimeUnit time_unit)

OTP 18.3

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

time_unit is time unit of returned value.

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

See also ErlDrvTime and ErlDrvTimeUnit.

void *erl_drv_tsd_get( ErlDrvTSDKey key)

Returns the thread-specific data associated with key for the calling thread.

key is a thread-specific data key.

Returns NULL if no data has been associated with key for the calling thread.

This function is thread-safe.

int erl_drv_tsd_key_create( char *name, ErlDrvTSDKey *key)

Creates a thread-specific data key.

name is a string identifying the created key. It is used to identify the key in planned future debug functionality.

key is a pointer to a thread-specific data key variable.

Returns 0 on success, otherwise an errno value is returned to indicate the error. The driver creating the key is responsible for destroying it before the driver is unloaded.

This function is thread-safe.

void erl_drv_tsd_key_destroy( ErlDrvTSDKey key)

Destroys a thread-specific data key previously created by erl_drv_tsd_key_create. All thread-specific data using this key in all threads must be cleared (see erl_drv_tsd_set) before the call to erl_drv_tsd_key_destroy.

key is a thread-specific data key to destroy.

This function is thread-safe.

void erl_drv_tsd_set( ErlDrvTSDKey key, void *data)

Sets thread-specific data associated with key for the calling thread. You are only allowed to set thread-specific data for threads while they are fully under your control. For example, if you set thread-specific data in a thread calling a driver callback function, it must be cleared, that is, set to NULL, before returning from the driver callback function.

key is a thread-specific data key.

data is a pointer to data to associate with key in the calling thread.

This function is thread-safe.

char *erl_errno_id( int error)

Returns the atom name of the Erlang error, given the error number in error. The error atoms are einval, enoent, and so on. It can be used to make error terms from the driver.

int remove_driver_entry( ErlDrvEntry *de)

Removes a driver entry de previously added with add_driver_entry.

Driver entries added by the erl_ddll Erlang interface cannot be removed by using this interface.

void set_busy_port( ErlDrvPort port, int on)

Sets and unsets the busy state of the port. If on is non-zero, the port is set to busy. If it is zero, the port is set to not busy. You typically want to combine this feature with the busy port message queue functionality.

Processes sending command data to the port are suspended if either the port or the port message queue is busy. Suspended processes are resumed when neither the port or the port message queue is busy. Command data is in this context data passed to the port using either Port ! {Owner, {command, Data}} or port_command/[2,3].

If the ERL_DRV_FLAG_SOFT_BUSY has been set in the driver_entry, data can be forced into the driver through erlang:port_command(Port, Data, [force]) even if the driver has signaled that it is busy.

For information about busy port message queue functionality, see erl_drv_busy_msgq_limits.

void set_port_control_flags( ErlDrvPort port, int flags)

Sets flags for how the control driver entry function will return data to the port owner process. (The control function is called from erlang:port_control/3.)

Currently there are only two meaningful values for flags: 0 means that data is returned in a list, and PORT_CONTROL_FLAG_BINARY means data is returned as a binary from control.