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-rw-r--r--erts/doc/src/driver_entry.xml16
-rw-r--r--erts/doc/src/erl_driver.xml81
2 files changed, 86 insertions, 11 deletions
diff --git a/erts/doc/src/driver_entry.xml b/erts/doc/src/driver_entry.xml
index a2efdf3ebc..d65a38570d 100644
--- a/erts/doc/src/driver_entry.xml
+++ b/erts/doc/src/driver_entry.xml
@@ -377,11 +377,11 @@ typedef struct erl_drv_entry {
<tag><marker id="driver_flags"/>int driver_flags</tag>
<item>
- <p>This field is used to pass driver capability information to the
- runtime system. If the <c>extended_marker</c> field equals
- <c>ERL_DRV_EXTENDED_MARKER</c>, it should contain <c>0</c> or
- driver flags (<c>ERL_DRV_FLAG_*</c>) ored bitwise. Currently
- the following driver flags exist:
+ <p>This field is used to pass driver capability and other
+ information to the runtime system. If the
+ <c>extended_marker</c> field equals <c>ERL_DRV_EXTENDED_MARKER</c>,
+ it should contain <c>0</c> or driver flags (<c>ERL_DRV_FLAG_*</c>)
+ ored bitwise. Currently the following driver flags exist:
</p>
<taglist>
<tag><c>ERL_DRV_FLAG_USE_PORT_LOCKING</c></tag>
@@ -404,6 +404,12 @@ typedef struct erl_drv_entry {
by the Erlang distribution (the behaviour has always been
required by drivers used by the distribution).
</item>
+ <tag><c>ERL_DRV_FLAG_NO_BUSY_MSGQ</c></tag>
+ <item>Disable busy port message queue functionality. For
+ more information, see the documentation of the
+ <seealso marker="erl_driver#erl_drv_busy_msgq_limits">erl_drv_busy_msgq_limits()</seealso>
+ function.
+ </item>
</taglist>
</item>
<tag>void *handle2</tag>
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>