Add skeleton for functionality and concurrency

mempool/docs/README.md

@@ -8,4 +8,4 @@ Components:
 * [Config](./config.md) - how to configure it
 * [External Messages](./messages.md) - The messages we accept over p2p and rpc interfaces
 * [Functionality](./functionality.md) - high-level description of the functionality it provides
-* [Local Services](./services.md) - Interfaces with consensus and abci services
+* [Concurrency Model](./concurrency.md) - What guarantees we provide, what locks we require.

mempool/docs/concurrency.md

@@ -0,0 +1,8 @@
+# Mempool Concurrency
+
+Look at the concurrency model this uses...
+
+* Receiving CheckTx
+* Broadcasting new tx
+* Interfaces with consensus engine, reap/update while checking
+* Calling the ABCI app (ordering. callbacks. how proxy works alongside the blockchain proxy which actually writes blocks)

mempool/docs/functionality.md

@@ -0,0 +1,37 @@
+# Mempool Functionality
+
+The mempool maintains a list of potentially valid transactions,
+both to broadcast to other nodes, as well as to provide to the
+consensus reactor when it is selected as the block proposer.
+
+There are two sides to the mempool state:
+
+* External: get, check, and broadcast new transactions
+* Internal: return valid transaction, update list after block commit
+
+
+## External functionality
+
+External functionality is exposed via network interfaces
+to potentially untrusted actors.
+
+* CheckTx - triggered via RPC or P2P
+* Broadcast - gossip messages after a successful check
+
+## Internal functionality
+
+Internal functionality is exposed via method calls to other
+code compiled into the tendermint binary.
+
+* Reap - get tx to propose in next block
+* Update - remove tx that were included in last block
+* ABCI.CheckTx - call ABCI app to validate the tx
+
+What does it provide the consensus reactor?
+What guarantees does it need from the ABCI app?
+(talk about interleaving processes in concurrency)
+
+## Optimizations
+
+Talk about the LRU cache to make sure we don't process any
+tx that we have seen before