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x/evm/handler.go

@@ -16,17 +16,31 @@ import (
 func NewHandler(k Keeper) sdk.Handler {
 	return func(ctx sdk.Context, msg sdk.Msg) (result *sdk.Result, err error) {
 		snapshotStateDB := k.CommitStateDB.Copy()
+
+		// The "recover" code here is used to solve the problem of dirty data
+		// in CommitStateDB due to insufficient gas.
+
+		// The following is a detailed description:
 		// If the gas is insufficient during the execution of the "handler",
 		// panic will be thrown from the function "ConsumeGas" and finally
 		// caught by the function "runTx" from Cosmos. The function "runTx"
 		// will think that the execution of Msg has failed and the modified
 		// data in the Store will not take effect.
-		// The fault is that the modified data in CommitStateDB has not been
-		// rolled back, resulting in bad data.
+
+		// Stacktrace：runTx->runMsgs->handler->...->gaskv.Store.Set->ConsumeGas
+
+		// The problem is that when the modified data in the Store does not take
+		// effect, the data in the modified CommitStateDB is not rolled back,
+		// they take effect, and dirty data is generated.
 		// Therefore, the code here specifically deals with this situation.
 		// See https://github.com/cosmos/ethermint/issues/668 for more information.
 		defer func() {
 			if r := recover(); r != nil {
+				// We first used "k.CommitStateDB = snapshotStateDB" to roll back
+				// CommitStateDB, but this can only change the CommitStateDB in the
+				// current Keeper object, tut the Keeper object will be destroyed
+				// soon, it is not a global variable, so the content pointed to by
+				// the CommitStateDB pointer can be modified to take effect.
 				types.CopyCommitStateDB(snapshotStateDB, k.CommitStateDB)
 				panic(r)
 			}