LlMessageLinked

From Second Life Wiki
Revision as of 11:23, 15 May 2008 by Lex Neva (Talk | contribs)

Jump to: navigation, search

Summary

Function: llMessageLinked( integer linknum, integer num, string str, key id );

Triggers a link_message event with the parameters num, str, and id in all scripts in the prim(s) described by linknum. The purpose of this function is to provide same object prim to prim communication.

• integer linknum Link number or a LINK_* flag.
• integer num Value of the second parameter of the resulting link_message event.
• string str Value of the third parameter of the resulting link_message event.
• key id Value of the forth parameter of the resulting link_message event.

You can use id as a second string field (in LSL the key type is implemented as a string with just custom operators). Typecasting between string and key types has no effect on the data contained. The sizes of str and id are only limited by available script memory.

Flag Description
LINK_ROOT 1 refers to the root prim in a multi-prim linked set[1]
LINK_SET -1 refers to all prims
LINK_ALL_OTHERS -2 refers to all other prims
Flag Description
LINK_ALL_CHILDREN -3 refers to all children, (everything but the root)
LINK_THIS -4 refers to the prim the script is in

Caveats

  • A script can hear its own linked messages if linknum would target the prim it is in (for example, LINK_SET). This creates the possibility of an infinite loop (a bad thing); be very careful about how messages are handled and passed along.
  • Messages sent via llMessageLinked to a script that is sleeping, delayed, or lagged, are queued until the end of the delay. The event queue can hold 64 events.
    • If an event is received and the queue is full the event is silently dropped.
    • It is possible to generate a script VM lag spike if the message is received by many scripts. This typically occurs when using LINK_SET, LINK_ALL_OTHERS, & LINK_ALL_CHILDREN as link_num. Script execution can slow or halts. If multiple messages are sent one after another, the lag can cause the event queue to fill.
    • Avoid sending link_messages to large numbers of scripts simultaneously.
    • Avoid sending link_messages to a target faster then they can be handled.
  • When a script state change, all pending events are deleted, including queued link_messages.
  • If link_num is an invalid link number then the function silently fails.
All Issues ~ Search JIRA for related Bugs

Examples

<lsl>default{ // assumptions // object name: LSLWiki // script name: _lslwiki

   state_entry() {
       llMessageLinked(LINK_THIS, 0, llGetScriptName(), "");
   }
   link_message(integer sender_num, integer num, string msg, key id) {
       llOwnerSay(msg);
       // the owner of object LSLWiki will hear
       // LSLWiki:_lslwiki
   }    
}</lsl>

Useful Snippets

<lsl>default { // Quick and dirty debugging link_messages

   link_message(integer sender_num, integer num, string msg, key id) {
       llSay(DEBUG_CHANNEL, llList2CSV([sender_num, num, msg, id]));
   }

}</lsl> <lsl>// This is just an example script, you shouldn't handle link message within single script this way.

default{ // To propagate an unlimted number of arguments of any type. // Presumed, the separator string isn't used in any source string!

   state_entry() {    
       list my_list = [1, 2.0, "a string", <1, 2, 3>, <1, 2, 3, 4>, llGetOwner()];  
       string list_parameter = llDumpList2String(my_list, "

Notes

Link Numbers

Each prim that makes up an object has an address, a link number. To access a specific prim in the object, the prim's link number must be known. In addition to prims having link numbers, avatars seated upon the object do as well.

  • If an object consists of only one prim, and there are no avatars seated upon it, the (root) prim's link number is zero.
  • However, if the object is made up of multiple prims or there is an avatar seated upon the object, the root prim's link number is one.

When an avatar sits on an object, it is added to the end of the link set and will have the largest link number. In addition to this, while an avatar is seated upon an object, the object is unable to link or unlink prims without unseating all avatars first.

Counting Prims & Avatars

There are two functions of interest when trying to find the number of prims and avatars on an object.

integer GetPrimCount() { //always returns only the number of prims
    if(llGetAttached())//Is it attached?
        return llGetNumberOfPrims();//returns avatars and prims but attachments can't be sat on.
    return llGetObjectPrimCount(llGetKey());//returns only prims but won't work on attachments.
}
See llGetNumberOfPrims for more about counting prims and avatars.

Errata

If a script located in a child prim erroneously attempts to access link 0, it will get or set the property of the linkset's root prim. This bug (BUG-5049) is preserved for broken legacy scripts.

  • Using llMessageLinked in a single prim object allows developers to mitigate some LSL limits by breaking up functionality between cooperating scripts and synchronizing actions. When you do this, be extremely careful not to create infinite loops as mentioned above.
  • Some users have noted occasional failures of linked messages when sending a message to a large number of receiving scripts in different prims using LINK_SET, LINK_ALL_OTHERS, & LINK_ALL_CHILDREN (ie. not all prims receive the message). If you encounter this problem, a workaround is to place all child prim scripts in a single prim, using targeted functions like llSetLinkPrimitiveParams to modify the prim in which the script previously resided, and use a single link message to address them. -- Void Singer

See Also

Events

•  link_message

Functions

•  llGetLinkNumber Returns the link number of the prim the script is in.

Deep Notes

Search JIRA for related Issues

Footnotes

  1. ^ LINK_ROOT does not work on single prim objects. Unless there is an avatar sitting on the object.

Signature

function void llMessageLinked( integer linknum, integer num, string str, key id );