Wait blocks

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Wait blocks are trigger-related issues in StarCraft maps. They occur when the game tries to execute two Wait actions at the same time. Only one Wait action may be run at a time, so if a second is encountered, it is forcibly delayed until the first completes.

Wait blocks commonly occur when a map's triggers use both Waits and Wait-based hyper triggers.

Inner workings of the Wait action

Wait actions do more than just delaying other trigger actions by a given amount of milliseconds. When StarCraft runs a trigger for a player and encounters a Wait action, it takes the triggers that it has already processed for that player, and re-processes them all. Then, the game delays the actions following the Wait. Consider a map with the following two triggers:

StarCraft Trigger [template]
Description:
Create a Marine every trigger cycle.
Players:
  • Player 1
Conditions:
  • Always
Actions:
  • Create 1 Terran Marine at Anywhere for Player 1.
  • Preserve trigger.

StarCraft Trigger [template]
Description:
Display a message, wait a full second, and display another message.
Players:
  • Player 1
Conditions:
  • Always
Actions:
  • Display for current player:Hello!
  • Wait 1000 milliseconds.
  • Display for current player:Goodbye!
  • Preserve trigger.

When those triggers are processed, StarCraft will do the following:

  • Create a Terran Marine for Player 1.
  • Display "Hello!" on Player 1's screen.
  • Process the Wait action, by re-executing all Player 1 triggers.
    • Create a Terran Marine for Player 1.
    • Wait for a full second.
  • Display "Goodbye!" on Player 1's screen.

That would be one trigger cycle.

Wait blocks

The problems come when two Waits exist for the same player. Consider these triggers:

StarCraft Trigger [template]
Description:
TRIGGER 1. Create a Marine, wait a full second, and create another Marine.
Players:
  • Player 1
Conditions:
  • Always
Actions:
  • Create 1 Terran Marine at Anywhere for Player 1.
  • Wait 1000 milliseconds.
  • Create 1 Terran SCV at Anywhere for Player 1.
  • Preserve trigger.

StarCraft Trigger [template]
Description:
TRIGGER 2. Display a message, wait a full second, and display another message.
Players:
  • Player 1
Conditions:
  • Always
Actions:
  • Display for current player:Hello!
  • Wait 1000 milliseconds.
  • Display for current player:Goodbye!
  • Preserve trigger.

When StarCraft processes those triggers, it will do the following:

  • First trigger round
  • Create a Terran Marine for Player 1.
    • Increase wait timer by 1000 (TRIGGER 1)
  • Display "Hello!" on Player 1's screen.
    • There is already a wait on the wait timer, so wait until it's over to continue
  • Wait for a full second. (TRIGGER 1)
  • Create a Terran SCV for Player 1.
    • Increase wait timer by 1000 (TRIGGER 2)
  • Next trigger round
  • Create a Terran Marine for Player 1.
    • There is already a wait on the wait timer, but it's from a previous round, so increase wait timer by 1000 (Trigger 1)
  • Wait for 2 seconds. (TRIGGER 1+2)
  • Next trigger round
  • Create a Terran SCV for Player 1.
  • Display for current player:Goodbye!
    • The Wait action here cannot be processed, because the game is already processing a Wait action. This Wait and any remaining actions in this trigger (TRIGGER 1) will be delayed.
    • Wait for a full second.
    • Execute any delayed trigger actions.
      • Process the delayed Wait from TRIGGER 1.
        • There are no Player 1 triggers before TRIGGER 1.
        • Wait for a full second.
      • Create a Terran Marine for Player 1.
  • Display "Goodbye!" on Player 1's screen.

That is a full trigger cycle. In simpler terms, here is what happens:

  • Create a Terran Marine for Player 1.
  • Display "Hello!"
  • Wait for a full second. (TRIGGER 1)
  • Create a Terran SCV for Player 1.
  • Create a Terran Marine for Player 1.
  • Wait for a full second. (TRIGGER 2)
  • Wait for a full second. (TRIGGER 1)
    • Essentially, the two waits are combined.
  • Create a Terran SCV for Player 1.
  • Display "Goodbye!"

In simple systems, this is often only a minor annoyance... But when large amounts of waits are used (as is the case when using Wait-based hyper triggers), the combined Wait time can cause a massive (or even infinitely long) wait block, completely breaking the map's triggers.

Why do Waits behave this way?

The reason that previous triggers are re-processed when a Wait is run is to prevent problems in the trigger system. If triggers were not re-processed, then for the above example, there would be a full second where no triggers can run. (This would translate to a full second in which no Marines are created.) In maps that need to detect things like unit locations and deaths, this would be a catastrophic delay. Any kind of map that requires precision or timing would end up completely broken. By re-processing the trigger list, StarCraft is able to delay trigger actions without breaking the trigger system. Wait blocks are simply an unanticipated problem in this system.

Solutions

  • When using Wait-based hyper triggers, set them up properly. Alternatively, switch to "complex" hyper triggers, which are (ironically) much easier to set up and maintain.
  • Avoid situations where a player could end up running multiple Waits at once.
  • Use different methods to keep track of time. Timers can use death counters, countdown timers, the movement of a unit from one location to another, or even the burning and destruction of a badly-damaged Terran building (using the death counters or Extended Unit Deaths to detect certain values.)

External links

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