diff options
Diffstat (limited to 'erts/doc/src/erl_driver.xml')
| -rw-r--r-- | erts/doc/src/erl_driver.xml | 81 |
1 files changed, 75 insertions, 6 deletions
diff --git a/erts/doc/src/erl_driver.xml b/erts/doc/src/erl_driver.xml index fcce962557..903b8dfe64 100644 --- a/erts/doc/src/erl_driver.xml +++ b/erts/doc/src/erl_driver.xml @@ -1500,16 +1500,81 @@ typedef struct ErlIOVec { </desc> </func> <func> + <name><ret>void</ret><nametext>erl_drv_busy_msgq_limits(ErlDrvPort port, ErlDrvSizeT *low, ErlDrvSizeT *high)</nametext></name> + <fsummary>Set and get limits for busy port message queue</fsummary> + <desc> + <marker id="erl_drv_busy_msgq_limits"></marker> + <p>Sets and gets limits that will be used for controling the + busy state of the port message queue.</p> + <p>The port message queue will be set into a busy + state when the amount of command data queued on the + message queue reaches the <c>high</c> limit. The port + message queue will be set into a not busy state when the + amount of command data queued on the message queue falls + below the <c>low</c> limit. Command data is in this + context data passed to the port using either + <c>Port ! {Owner, {command, Data}}</c>, or + <c>port_command/[2,3]</c>. Note that these limits + only concerns command data that have not yet reached the + port. The <seealso marker="#set_busy_port">busy port</seealso> + feature can be used for data that has reached the port.</p> + + <p>Valid limits are values in the range + <c>[ERL_DRV_BUSY_MSGQ_LIM_MIN, ERL_DRV_BUSY_MSGQ_LIM_MAX]</c>. + Limits will be automatically adjusted to be sane. That is, + the system will adjust values so that the low limit used is + lower or equal to the high limit used. By default the high + limit will be 8 kB and the low limit will be 4 kB.</p> + + <p>By passing a pointer to an integer variable containing + the value <c>ERL_DRV_BUSY_MSGQ_READ_ONLY</c>, currently used + limit will be 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 will be + written to the internal limit. The internal limit will then + be adjusted. After this the adjusted limit will be written + back to the integer variable from which the new value was + read. Values are in bytes.</p> + + <p>The busy message queue feature can be disabled either + by setting the <c>ERL_DRV_FLAG_NO_BUSY_MSGQ</c> + <seealso marker="driver_entry#driver_flags">driver flag</seealso> + in the <seealso marker="driver_entry">driver_entry</seealso> + used by the driver, or by calling this function with + <c>ERL_DRV_BUSY_MSGQ_DISABLED</c> as a limit (either low or + high). When this feature has been disabled it cannot be + enabled again. When reading the limits both of them + will be <c>ERL_DRV_BUSY_MSGQ_DISABLED</c>, if this + feature has been disabled.</p> + + <p>Processes sending command data to the port will be suspended + if either the port is busy or if the port message queue is + busy. Suspended processes will be resumed when neither the + port is busy, nor the port message queue is busy.</p> + + <p>For information about busy port functionality + see the documentation of the + <seealso marker="#set_busy_port">set_busy_port()</seealso> + function.</p> + </desc> + </func> + <func> <name><ret>void</ret><nametext>set_busy_port(ErlDrvPort port, int on)</nametext></name> <fsummary>Signal or unsignal port as busy</fsummary> <desc> <marker id="set_busy_port"></marker> - <p>This function set and resets the busy status of the port. If - <c>on</c> is 1, the port is set to busy, if it's 0 the port - is set to not busy.</p> - <p>When the port is busy, sending to it with <c>Port ! Data</c> - or <c>port_command/2</c>, will block the port owner process, - until the port is signaled as not busy.</p> + <p>This function set and unset the busy state of the port. If + <c>on</c> is non-zero, the port is set to busy, if it's zero the port + is set to not busy. You typically want to combine + this feature with the <seealso marker="#erl_drv_busy_msgq_limits">busy + port message queue</seealso> functionality.</p> + <p>Processes sending command data to the port will be suspended + if either the port is busy or if the port message queue + is busy. Suspended processes will be resumed when neither the + port is busy, nor the port message queue is busy. Command data + is in this context data passed to the port using either + <c>Port ! {Owner, {command, Data}}</c>, or + <c>port_command/[2,3]</c>.</p> <p>If the <seealso marker="driver_entry#driver_flags"><![CDATA[ERL_DRV_FLAG_SOFT_BUSY]]></seealso> has been set in the @@ -1518,6 +1583,10 @@ typedef struct ErlIOVec { <seealso marker="erlang#port_command/3">port_command(Port, Data, [force])</seealso> even though the driver has signaled that it is busy. </p> + <p>For information about busy port message queue functionality + see the documentation of the + <seealso marker="#erl_drv_busy_msgq_limits">erl_drv_busy_msgq_limits()</seealso> + function.</p> </desc> </func> <func> |