FixedUpdate schedules that take too long enter a cascading failure mode
#8543
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alice-i-cecile
added
C-Bug
|
@maniwani, I'm observing this in practice with my game at high enough simulation loads. I think we should be putting some sort of limitation in place here, but I'm not sure what the right fix is. |
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Initially, you can see one or two fixed updates (purple s) per frame (tall skinny rendering thread) https://cdn.discordapp.com/attachments/1103705291461230602/1103724366778347612/image.png Later, dozens of them per frame: https://cdn.discordapp.com/attachments/1103705291461230602/1103724645129130014/image.png |
alice-i-cecile
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alice-i-cecile
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alice-i-cecile
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* Increase map size to reproduce the problem * Add workaround for bevyengine/bevy#8543 * Don't freeze the game lol
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# Objective Current `FixedTime` and `Time` have several problems. This pull aims to fix many of them at once. - If there is a longer pause between app updates, time will jump forward a lot at once and fixed time will iterate on `FixedUpdate` for a large number of steps. If the pause is merely seconds, then this will just mean jerkiness and possible unexpected behaviour in gameplay. If the pause is hours/days as with OS suspend, the game will appear to freeze until it has caught up with real time. - If calculating a fixed step takes longer than specified fixed step period, the game will enter a death spiral where rendering each frame takes longer and longer due to more and more fixed step updates being run per frame and the game appears to freeze. - There is no way to see current fixed step elapsed time inside fixed steps. In order to track this, the game designer needs to add a custom system inside `FixedUpdate` that calculates elapsed or step count in a resource. - Access to delta time inside fixed step is `FixedStep::period` rather than `Time::delta`. This, coupled with the issue that `Time::elapsed` isn't available at all for fixed steps, makes it that time requiring systems are either implemented to be run in `FixedUpdate` or `Update`, but rarely work in both. - Fixes #8800 - Fixes #8543 - Fixes #7439 - Fixes #5692 ## Solution - Create a generic `Time<T>` clock that has no processing logic but which can be instantiated for multiple usages. This is also exposed for users to add custom clocks. - Create three standard clocks, `Time<Real>`, `Time<Virtual>` and `Time<Fixed>`, all of which contain their individual logic. - Create one "default" clock, which is just `Time` (or `Time<()>`), which will be overwritten from `Time<Virtual>` on each update, and `Time<Fixed>` inside `FixedUpdate` schedule. This way systems that do not care specifically which time they track can work both in `Update` and `FixedUpdate` without changes and the behaviour is intuitive. - Add `max_delta` to virtual time update, which limits how much can be added to virtual time by a single update. This fixes both the behaviour after a long freeze, and also the death spiral by limiting how many fixed timestep iterations there can be per update. Possible future work could be adding `max_accumulator` to add a sort of "leaky bucket" time processing to possibly smooth out jumps in time while keeping frame rate stable. - Many minor tweaks and clarifications to the time functions and their documentation. ## Changelog - `Time::raw_delta()`, `Time::raw_elapsed()` and related methods are moved to `Time<Real>::delta()` and `Time<Real>::elapsed()` and now match `Time` API - `FixedTime` is now `Time<Fixed>` and matches `Time` API. - `Time<Fixed>` default timestep is now 64 Hz, or 15625 microseconds. - `Time` inside `FixedUpdate` now reflects fixed timestep time, making systems portable between `Update ` and `FixedUpdate`. - `Time::pause()`, `Time::set_relative_speed()` and related methods must now be called as `Time<Virtual>::pause()` etc. - There is a new `max_delta` setting in `Time<Virtual>` that limits how much the clock can jump by a single update. The default value is 0.25 seconds. - Removed `on_fixed_timer()` condition as `on_timer()` does the right thing inside `FixedUpdate` now. ## Migration Guide - Change all `Res<Time>` instances that access `raw_delta()`, `raw_elapsed()` and related methods to `Res<Time<Real>>` and `delta()`, `elapsed()`, etc. - Change access to `period` from `Res<FixedTime>` to `Res<Time<Fixed>>` and use `delta()`. - The default timestep has been changed from 60 Hz to 64 Hz. If you wish to restore the old behaviour, use `app.insert_resource(Time::<Fixed>::from_hz(60.0))`. - Change `app.insert_resource(FixedTime::new(duration))` to `app.insert_resource(Time::<Fixed>::from_duration(duration))` - Change `app.insert_resource(FixedTime::new_from_secs(secs))` to `app.insert_resource(Time::<Fixed>::from_seconds(secs))` - Change `system.on_fixed_timer(duration)` to `system.on_timer(duration)`. Timers in systems placed in `FixedUpdate` schedule automatically use the fixed time clock. - Change `ResMut<Time>` calls to `pause()`, `is_paused()`, `set_relative_speed()` and related methods to `ResMut<Time<Virtual>>` calls. The API is the same, with the exception that `relative_speed()` will return the actual last ste relative speed, while `effective_relative_speed()` returns 0.0 if the time is paused and corresponds to the speed that was set when the update for the current frame started. ## Todo - [x] Update pull name and description - [x] Top level documentation on usage - [x] Fix examples - [x] Decide on default `max_delta` value - [x] Decide naming of the three clocks: is `Real`, `Virtual`, `Fixed` good? - [x] Decide if the three clock inner structures should be in prelude - [x] Decide on best way to configure values at startup: is manually inserting a new clock instance okay, or should there be config struct separately? - [x] Fix links in docs - [x] Decide what should be public and what not - [x] Decide how `wrap_period` should be handled when it is changed - [x] ~~Add toggles to disable setting the clock as default?~~ No, separate pull if needed. - [x] Add tests - [x] Reformat, ensure adheres to conventions etc. - [x] Build documentation and see that it looks correct ## Contributors Huge thanks to @alice-i-cecile and @maniwani while building this pull. It was a shared effort! --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: Cameron <51241057+maniwani@users.noreply.github.com> Co-authored-by: Jerome Humbert <djeedai@gmail.com>
ameknite
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…e#8964) # Objective Current `FixedTime` and `Time` have several problems. This pull aims to fix many of them at once. - If there is a longer pause between app updates, time will jump forward a lot at once and fixed time will iterate on `FixedUpdate` for a large number of steps. If the pause is merely seconds, then this will just mean jerkiness and possible unexpected behaviour in gameplay. If the pause is hours/days as with OS suspend, the game will appear to freeze until it has caught up with real time. - If calculating a fixed step takes longer than specified fixed step period, the game will enter a death spiral where rendering each frame takes longer and longer due to more and more fixed step updates being run per frame and the game appears to freeze. - There is no way to see current fixed step elapsed time inside fixed steps. In order to track this, the game designer needs to add a custom system inside `FixedUpdate` that calculates elapsed or step count in a resource. - Access to delta time inside fixed step is `FixedStep::period` rather than `Time::delta`. This, coupled with the issue that `Time::elapsed` isn't available at all for fixed steps, makes it that time requiring systems are either implemented to be run in `FixedUpdate` or `Update`, but rarely work in both. - Fixes bevyengine#8800 - Fixes bevyengine#8543 - Fixes bevyengine#7439 - Fixes bevyengine#5692 ## Solution - Create a generic `Time<T>` clock that has no processing logic but which can be instantiated for multiple usages. This is also exposed for users to add custom clocks. - Create three standard clocks, `Time<Real>`, `Time<Virtual>` and `Time<Fixed>`, all of which contain their individual logic. - Create one "default" clock, which is just `Time` (or `Time<()>`), which will be overwritten from `Time<Virtual>` on each update, and `Time<Fixed>` inside `FixedUpdate` schedule. This way systems that do not care specifically which time they track can work both in `Update` and `FixedUpdate` without changes and the behaviour is intuitive. - Add `max_delta` to virtual time update, which limits how much can be added to virtual time by a single update. This fixes both the behaviour after a long freeze, and also the death spiral by limiting how many fixed timestep iterations there can be per update. Possible future work could be adding `max_accumulator` to add a sort of "leaky bucket" time processing to possibly smooth out jumps in time while keeping frame rate stable. - Many minor tweaks and clarifications to the time functions and their documentation. ## Changelog - `Time::raw_delta()`, `Time::raw_elapsed()` and related methods are moved to `Time<Real>::delta()` and `Time<Real>::elapsed()` and now match `Time` API - `FixedTime` is now `Time<Fixed>` and matches `Time` API. - `Time<Fixed>` default timestep is now 64 Hz, or 15625 microseconds. - `Time` inside `FixedUpdate` now reflects fixed timestep time, making systems portable between `Update ` and `FixedUpdate`. - `Time::pause()`, `Time::set_relative_speed()` and related methods must now be called as `Time<Virtual>::pause()` etc. - There is a new `max_delta` setting in `Time<Virtual>` that limits how much the clock can jump by a single update. The default value is 0.25 seconds. - Removed `on_fixed_timer()` condition as `on_timer()` does the right thing inside `FixedUpdate` now. ## Migration Guide - Change all `Res<Time>` instances that access `raw_delta()`, `raw_elapsed()` and related methods to `Res<Time<Real>>` and `delta()`, `elapsed()`, etc. - Change access to `period` from `Res<FixedTime>` to `Res<Time<Fixed>>` and use `delta()`. - The default timestep has been changed from 60 Hz to 64 Hz. If you wish to restore the old behaviour, use `app.insert_resource(Time::<Fixed>::from_hz(60.0))`. - Change `app.insert_resource(FixedTime::new(duration))` to `app.insert_resource(Time::<Fixed>::from_duration(duration))` - Change `app.insert_resource(FixedTime::new_from_secs(secs))` to `app.insert_resource(Time::<Fixed>::from_seconds(secs))` - Change `system.on_fixed_timer(duration)` to `system.on_timer(duration)`. Timers in systems placed in `FixedUpdate` schedule automatically use the fixed time clock. - Change `ResMut<Time>` calls to `pause()`, `is_paused()`, `set_relative_speed()` and related methods to `ResMut<Time<Virtual>>` calls. The API is the same, with the exception that `relative_speed()` will return the actual last ste relative speed, while `effective_relative_speed()` returns 0.0 if the time is paused and corresponds to the speed that was set when the update for the current frame started. ## Todo - [x] Update pull name and description - [x] Top level documentation on usage - [x] Fix examples - [x] Decide on default `max_delta` value - [x] Decide naming of the three clocks: is `Real`, `Virtual`, `Fixed` good? - [x] Decide if the three clock inner structures should be in prelude - [x] Decide on best way to configure values at startup: is manually inserting a new clock instance okay, or should there be config struct separately? - [x] Fix links in docs - [x] Decide what should be public and what not - [x] Decide how `wrap_period` should be handled when it is changed - [x] ~~Add toggles to disable setting the clock as default?~~ No, separate pull if needed. - [x] Add tests - [x] Reformat, ensure adheres to conventions etc. - [x] Build documentation and see that it looks correct ## Contributors Huge thanks to @alice-i-cecile and @maniwani while building this pull. It was a shared effort! --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: Cameron <51241057+maniwani@users.noreply.github.com> Co-authored-by: Jerome Humbert <djeedai@gmail.com>
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…e#8964) # Objective Current `FixedTime` and `Time` have several problems. This pull aims to fix many of them at once. - If there is a longer pause between app updates, time will jump forward a lot at once and fixed time will iterate on `FixedUpdate` for a large number of steps. If the pause is merely seconds, then this will just mean jerkiness and possible unexpected behaviour in gameplay. If the pause is hours/days as with OS suspend, the game will appear to freeze until it has caught up with real time. - If calculating a fixed step takes longer than specified fixed step period, the game will enter a death spiral where rendering each frame takes longer and longer due to more and more fixed step updates being run per frame and the game appears to freeze. - There is no way to see current fixed step elapsed time inside fixed steps. In order to track this, the game designer needs to add a custom system inside `FixedUpdate` that calculates elapsed or step count in a resource. - Access to delta time inside fixed step is `FixedStep::period` rather than `Time::delta`. This, coupled with the issue that `Time::elapsed` isn't available at all for fixed steps, makes it that time requiring systems are either implemented to be run in `FixedUpdate` or `Update`, but rarely work in both. - Fixes bevyengine#8800 - Fixes bevyengine#8543 - Fixes bevyengine#7439 - Fixes bevyengine#5692 ## Solution - Create a generic `Time<T>` clock that has no processing logic but which can be instantiated for multiple usages. This is also exposed for users to add custom clocks. - Create three standard clocks, `Time<Real>`, `Time<Virtual>` and `Time<Fixed>`, all of which contain their individual logic. - Create one "default" clock, which is just `Time` (or `Time<()>`), which will be overwritten from `Time<Virtual>` on each update, and `Time<Fixed>` inside `FixedUpdate` schedule. This way systems that do not care specifically which time they track can work both in `Update` and `FixedUpdate` without changes and the behaviour is intuitive. - Add `max_delta` to virtual time update, which limits how much can be added to virtual time by a single update. This fixes both the behaviour after a long freeze, and also the death spiral by limiting how many fixed timestep iterations there can be per update. Possible future work could be adding `max_accumulator` to add a sort of "leaky bucket" time processing to possibly smooth out jumps in time while keeping frame rate stable. - Many minor tweaks and clarifications to the time functions and their documentation. ## Changelog - `Time::raw_delta()`, `Time::raw_elapsed()` and related methods are moved to `Time<Real>::delta()` and `Time<Real>::elapsed()` and now match `Time` API - `FixedTime` is now `Time<Fixed>` and matches `Time` API. - `Time<Fixed>` default timestep is now 64 Hz, or 15625 microseconds. - `Time` inside `FixedUpdate` now reflects fixed timestep time, making systems portable between `Update ` and `FixedUpdate`. - `Time::pause()`, `Time::set_relative_speed()` and related methods must now be called as `Time<Virtual>::pause()` etc. - There is a new `max_delta` setting in `Time<Virtual>` that limits how much the clock can jump by a single update. The default value is 0.25 seconds. - Removed `on_fixed_timer()` condition as `on_timer()` does the right thing inside `FixedUpdate` now. ## Migration Guide - Change all `Res<Time>` instances that access `raw_delta()`, `raw_elapsed()` and related methods to `Res<Time<Real>>` and `delta()`, `elapsed()`, etc. - Change access to `period` from `Res<FixedTime>` to `Res<Time<Fixed>>` and use `delta()`. - The default timestep has been changed from 60 Hz to 64 Hz. If you wish to restore the old behaviour, use `app.insert_resource(Time::<Fixed>::from_hz(60.0))`. - Change `app.insert_resource(FixedTime::new(duration))` to `app.insert_resource(Time::<Fixed>::from_duration(duration))` - Change `app.insert_resource(FixedTime::new_from_secs(secs))` to `app.insert_resource(Time::<Fixed>::from_seconds(secs))` - Change `system.on_fixed_timer(duration)` to `system.on_timer(duration)`. Timers in systems placed in `FixedUpdate` schedule automatically use the fixed time clock. - Change `ResMut<Time>` calls to `pause()`, `is_paused()`, `set_relative_speed()` and related methods to `ResMut<Time<Virtual>>` calls. The API is the same, with the exception that `relative_speed()` will return the actual last ste relative speed, while `effective_relative_speed()` returns 0.0 if the time is paused and corresponds to the speed that was set when the update for the current frame started. ## Todo - [x] Update pull name and description - [x] Top level documentation on usage - [x] Fix examples - [x] Decide on default `max_delta` value - [x] Decide naming of the three clocks: is `Real`, `Virtual`, `Fixed` good? - [x] Decide if the three clock inner structures should be in prelude - [x] Decide on best way to configure values at startup: is manually inserting a new clock instance okay, or should there be config struct separately? - [x] Fix links in docs - [x] Decide what should be public and what not - [x] Decide how `wrap_period` should be handled when it is changed - [x] ~~Add toggles to disable setting the clock as default?~~ No, separate pull if needed. - [x] Add tests - [x] Reformat, ensure adheres to conventions etc. - [x] Build documentation and see that it looks correct ## Contributors Huge thanks to @alice-i-cecile and @maniwani while building this pull. It was a shared effort! --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: Cameron <51241057+maniwani@users.noreply.github.com> Co-authored-by: Jerome Humbert <djeedai@gmail.com>
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Bevy version
0.10
What you did
Run a fixed time schedule that takes longer to complete than the allocated time.
What went wrong
As the schedule took longer than the
FixedTime::period, the accumulated time increases.The next time we need to run the fixed update schedule, we must run it more times in order to catch up.
This puts us even further behind, worsening the problem...
The text was updated successfully, but these errors were encountered: