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P2P: improve RX/TX flow control

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1) "optimistic write": Push each message to kernel socket buffer immediately.

2) If there is write data at select time, that implies send() blocked
   during optimistic write.  Drain write queue, before receiving
   any more messages.

This avoids needlessly queueing received data, if the remote peer
is not themselves receiving data.

Result: write buffer (and thus memory usage) is kept small, DoS
potential is slightly lower, and TCP flow control signalling is
properly utilized.

The kernel will queue data into the socket buffer, then signal the
remote peer to stop sending data, until we resume reading again.
This commit is contained in:
Jeff Garzik 2012-11-15 18:20:26 -05:00 committed by Pieter Wuille
parent bc2f5aa72c
commit b9ff2970b9
2 changed files with 15 additions and 6 deletions
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16
src/net.cpp
View file

@ -855,14 +855,18 @@ void ThreadSocketHandler2(void* parg)
{
if (pnode->hSocket == INVALID_SOCKET)
continue;
FD_SET(pnode->hSocket, &fdsetRecv);
FD_SET(pnode->hSocket, &fdsetError);
hSocketMax = max(hSocketMax, pnode->hSocket);
have_fds = true;
{
TRY_LOCK(pnode->cs_vSend, lockSend);
if (lockSend && !pnode->vSend.empty())
FD_SET(pnode->hSocket, &fdsetSend);
if (lockSend) {
// do not read, if draining write queue
if (!pnode->vSend.empty())
FD_SET(pnode->hSocket, &fdsetSend);
else
FD_SET(pnode->hSocket, &fdsetRecv);
FD_SET(pnode->hSocket, &fdsetError);
hSocketMax = max(hSocketMax, pnode->hSocket);
have_fds = true;
}
}
}
}

5
src/net.h
View file

@ -42,6 +42,7 @@ unsigned short GetListenPort();
bool BindListenPort(const CService &bindAddr, std::string& strError=REF(std::string()));
void StartNode(void* parg);
bool StopNode();
void SocketSendData(CNode *pnode);
enum
{
@ -437,6 +438,10 @@ public:
printf("(%d bytes)\n", nSize);
}
// If write queue empty, attempt "optimistic write"
if (nHeaderStart == 0)
SocketSendData(this);
nHeaderStart = -1;
nMessageStart = -1;
LEAVE_CRITICAL_SECTION(cs_vSend);