be12136b8a
Add `STObject` constructor to explicitly set the inner object template. This allows certain AMM transactions to apply in the same ledger: There is no issue if the trading fee is greater than or equal to 0.01%. If the trading fee is less than 0.01%, then: - After AMM create, AMM transactions must wait for one ledger to close (3-5 seconds). - After one ledger is validated, all AMM transactions succeed, as appropriate, except for AMMVote. - The first AMMVote which votes for a 0 trading fee in a ledger will succeed. Subsequent AMMVote transactions which vote for a 0 trading fee will wait for the next ledger (3-5 seconds). This behavior repeats for each ledger. This has no effect on the ultimate correctness of AMM. This amendment will allow the transactions described above to succeed as expected, even if the trading fee is 0 and the transactions are applied within one ledger (block).
How to use RPC coroutines.
Introduction.
By default, an RPC handler runs as an uninterrupted task on the JobQueue. This is fine for commands that are fast to compute but might not be acceptable for tasks that require multiple parts or are large, like a full ledger.
For this purpose, the rippled RPC handler allows suspension with continuation
- a request to suspend execution of the RPC response and to continue it after some function or job has been executed. A default continuation is supplied which simply reschedules the job on the JobQueue, or the programmer can supply their own.
The classes.
Suspension with continuation uses four std::functions in the ripple::RPC
namespace:
using Callback = std::function <void ()>;
using Continuation = std::function <void (Callback const&)>;
using Suspend = std::function <void (Continuation const&)>;
using Coroutine = std::function <void (Suspend const&)>;
A Callback is a generic 0-argument function. A given Callback might or might
not block. Unless otherwise advised, do not hold locks or any resource that
would prevent any other task from making forward progress when you call a
Callback.
A Continuation is a function that is given a Callback and promises to call
it later. A Continuation guarantees to call the Callback exactly once at
some point in the future, but it does not have to be immediately or even in the
current thread.
A Suspend is a function belonging to a Coroutine. A Suspend runs a
Continuation, passing it a Callback that continues execution of the
Coroutine.
And finally, a Coroutine is a std::function which is given a
Suspend. This is what the RPC handler gives to the coroutine manager,
expecting to get called back with a Suspend and to be able to start execution.
The flow of control.
Given these functions, the flow of RPC control when using coroutines is straight-forward.
-
The instance of
ServerHandlerreceives an RPC request. -
It creates a
Coroutineand gives it to the coroutine manager. -
The coroutine manager creates a
Coroutine, starts it up, and then calls theCoroutinewith aSuspend. -
Now the RPC response starts to be calculated.
-
When the RPC handler wants to suspend, it calls the
Suspendfunction with aContinuation. -
Coroutine execution is suspended.
-
The
Continuationis called with aCallbackthat the coroutine manager creates. -
The
Continuationmay choose to execute immediately, defer execution on the job queue, or wait for some resource to be free. -
When the
Continuationis finished, it calls theCallbackthat the coroutine manager gave it, perhaps a long time ago. -
This
Callbackcontinues execution on the suspendedCoroutinefrom where it left off.