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Weight Refunds mechanism RFC #5032

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Weight Refunds mechanism RFC #5032

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069c83d
Introduce `Dispatcher` trait.
pepyakin Feb 20, 2020
9a2ceef
Initial sketch
pepyakin Feb 24, 2020
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9 changes: 4 additions & 5 deletions frame/support/src/traits.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,14 +18,13 @@
//!
//! NOTE: If you're looking for `parameter_types`, it has moved in to the top-level module.

use sp_std::{prelude::*, result, marker::PhantomData, ops::Div, fmt::Debug};
use codec::{FullCodec, Codec, Encode, Decode};
use codec::{Codec, Decode, Encode, FullCodec};
use sp_core::u32_trait::Value as U32;
use sp_runtime::{
RuntimeDebug,
ConsensusEngineId, DispatchResult, DispatchError,
traits::{MaybeSerializeDeserialize, AtLeast32Bit, Saturating, TrailingZeroInput},
traits::{AtLeast32Bit, MaybeSerializeDeserialize, Saturating, TrailingZeroInput},
ConsensusEngineId, DispatchError, DispatchResult, RuntimeDebug,
};
use sp_std::{fmt::Debug, marker::PhantomData, ops::Div, prelude::*, result};

use crate::dispatch::Parameter;
use crate::storage::StorageMap;
Expand Down
67 changes: 66 additions & 1 deletion frame/system/src/lib.rs
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Expand Up @@ -108,6 +108,7 @@ use sp_runtime::{
self, CheckEqual, AtLeast32Bit, Zero, SignedExtension, Lookup, LookupError,
SimpleBitOps, Hash, Member, MaybeDisplay, EnsureOrigin, BadOrigin, SaturatedConversion,
MaybeSerialize, MaybeSerializeDeserialize, MaybeMallocSizeOf, StaticLookup, One, Bounded,
Dispatchable
},
};

Expand All @@ -118,7 +119,7 @@ use frame_support::{
Contains, Get, ModuleToIndex, OnNewAccount, OnKilledAccount, IsDeadAccount, Happened,
StoredMap
},
weights::{Weight, DispatchInfo, DispatchClass, SimpleDispatchInfo, FunctionOf},
weights::{Weight, DispatchInfo, GetDispatchInfo, DispatchClass, SimpleDispatchInfo, FunctionOf},
};
use codec::{Encode, Decode, FullCodec, EncodeLike};

Expand Down Expand Up @@ -348,6 +349,9 @@ decl_storage! {
/// Total weight for all extrinsics put together, for the current block.
AllExtrinsicsWeight: Option<Weight>;

/// The weight taken by the current executing disptachable.
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@athei athei Mar 2, 2020

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typo: disptachable

CurrentDispatchableWeight: Option<Weight>;

/// Total length (in bytes) for all extrinsics put together, for the current block.
AllExtrinsicsLen: Option<u32>;

Expand Down Expand Up @@ -1022,6 +1026,57 @@ impl<T: Trait> Module<T> {
}
}

impl<T: Trait> Module<T> {
pub fn spent_weight() -> Option<Weight> {
CurrentDispatchableWeight::get()
}

/// Decrease the amount of weight consumed by the current dispatchable.
///
/// This function can only meaningfully called within `Self::dispatch`. Otherwise,
/// it does nothing and returns `Err`.
///
/// The total weight returned from the dispatchable cannot exceed its total requested weight.
pub fn return_unspent_weight(unspent: Weight) -> Result<(), ()> {
let weight = CurrentDispatchableWeight::take().ok_or(())?;
let next_weight = weight.checked_sub(unspent).ok_or(())?;
CurrentDispatchableWeight::put(next_weight);
Ok(())
}
}

impl<T: Trait> Module<T>
where
<T as Trait>::Call: GetDispatchInfo + Dispatchable,
{
/// Dispatch a given `T::Call` with a given origin.
///
/// Returns how much weight was actually unspent by the call.
pub fn dispatch_call(
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@kianenigma kianenigma Feb 25, 2020

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Suggested change
pub fn dispatch_call(
pub fn note_dispatch_call(

There should really be an emphasis on the fact that this some bookkeeping for you. Chose some other name if you want, but dispatch_call is too simple.

origin: <T::Call as Dispatchable>::Origin,
call: T::Call,
) -> (Weight, sp_runtime::DispatchResult) {
// First, replace the current weight counter with the incoming call weight.
let prev_weight = CurrentDispatchableWeight::get();
let call_weight = call.get_dispatch_info().weight;
CurrentDispatchableWeight::put(call_weight);

// Then, dispatch the call.
let result = call.dispatch(origin);

// Finally, get the actual spent weight.
let spent_weight = CurrentDispatchableWeight::take().unwrap_or_default();
if let Some(prev_weight) = prev_weight {
CurrentDispatchableWeight::put(prev_weight);
} else {
CurrentDispatchableWeight::kill();
}

let unspent_weight = call_weight.saturating_sub(spent_weight);
(unspent_weight, result)
}
}

/// Event handler which calls on_created_account when it happens.
pub struct CallOnCreatedAccount<T>(PhantomData<T>);
impl<T: Trait> Happened<T::AccountId> for CallOnCreatedAccount<T> {
Expand Down Expand Up @@ -1246,6 +1301,16 @@ impl<T: Trait + Send + Sync> SignedExtension for CheckWeight<T> {
) -> TransactionValidity {
Self::do_validate(info, len)
}

fn post_dispatch(_pre: Self::Pre, info: Self::DispatchInfo, _len: usize) {
let spent = CurrentDispatchableWeight::get().unwrap_or(info.weight);
let reserved = info.weight;
let unspent = spent - reserved;
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@athei athei Mar 2, 2020

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I think a comment why unchecked math is OK here is in order.

AllExtrinsicsWeight::mutate(|weight| {
let next_weight = weight.map(|weight| weight - unspent);
*weight = next_weight;
});
}
}

impl<T: Trait + Send + Sync> Debug for CheckWeight<T> {
Expand Down
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