Wallet out-of-memory crash on synchronization

[braydonf]

Summary

Under certain conditions a wallet will run out of memory when syncing.

Reproduce

It's somewhat difficult to reproduce this case. For the process to be out-of-memory, the rate that the wallet processes and adds blocks needs to be slower than the rate that blocks are added to the chain. This set of conditions are likely more relevant to an SPV node and wallet, however it could apply in any case. What happens is that there are many transactions and blocks that pile up in memory in a queue. That queue is the jobs field of the txLock from bmutex in the wdb database .

[braydonf]

A temporary solution:

Use emitAsync and an async function for the wallet adding blocks, similar to how chain will wait for the indexers. This will only work when the wallet is in the same process as a plugin, and not when the wallet is running as a separate process. This can work as a temporary solution for the SPV node.

diff --git a/lib/wallet/nodeclient.js b/lib/wallet/nodeclient.js
index 272e45094..89d9818f4 100644
--- a/lib/wallet/nodeclient.js
+++ b/lib/wallet/nodeclient.js
@@ -36,18 +36,18 @@ class NodeClient extends AsyncEmitter {
    */
 
   init() {
-    this.node.on('connect', (entry, block) => {
+    this.node.chain.on('connect', async (entry, block) => {
       if (!this.opened)
         return;
 
-      this.emit('block connect', entry, block.txs);
+      await this.emitAsync('block connect', entry, block.txs);
     });
 
     this.node.on('tx', (tx) => {

[braydonf]

This is addressed in part by #932. For the wallet as a process, there will need to be another fix.