http2: making sending to the socket more efficient

PR-URL: #15693
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

Author: jasnell

benchmark/http2/write.js

@@ -6,17 +6,27 @@ const PORT = common.PORT;
 const bench = common.createBenchmark(main, {
   streams: [100, 200, 1000],
   length: [64 * 1024, 128 * 1024, 256 * 1024, 1024 * 1024],
+  size: [100000]
 }, { flags: ['--expose-http2', '--no-warnings'] });
 
 function main(conf) {
   const m = +conf.streams;
   const l = +conf.length;
+  const s = +conf.size;
   const http2 = require('http2');
   const server = http2.createServer();
   server.on('stream', (stream) => {
     stream.respond();
-    stream.write('ü'.repeat(l));
-    stream.end();
+    let written = 0;
+    function write() {
+      stream.write('ü'.repeat(s));
+      written += s;
+      if (written < l)
+        setImmediate(write);
+      else
+        stream.end();
+    }
+    write();
   });
   server.listen(PORT, () => {
     bench.http({

src/node_http2_core-inl.h

@@ -478,25 +478,54 @@ inline void Nghttp2Session::SendPendingData() {
   // will not be usable.
   if (IsDestroying())
     return;
-  const uint8_t* data;
-  ssize_t len = 0;
-  size_t ncopy = 0;
-  uv_buf_t buf;
-  AllocateSend(SEND_BUFFER_RECOMMENDED_SIZE, &buf);
-  while (nghttp2_session_want_write(session_)) {
-    len = nghttp2_session_mem_send(session_, &data);
-    CHECK_GE(len, 0);  // If this is less than zero, we're out of memory
-    // While len is greater than 0, send a chunk
-    while (len > 0) {
-      ncopy = len;
-      if (ncopy > buf.len)
-        ncopy = buf.len;
-      memcpy(buf.base, data, ncopy);
-      Send(&buf, ncopy);
-      len -= ncopy;
-      CHECK_GE(len, 0);  // This should never be less than zero
+
+  uv_buf_t dest;
+  AllocateSend(SEND_BUFFER_RECOMMENDED_SIZE, &dest);
+  size_t destLength = 0;             // amount of data stored in dest
+  size_t destRemaining = dest.len;   // amount space remaining in dest
+  size_t destOffset = 0;             // current write offset of dest
+
+  const uint8_t* src;                // pointer to the serialized data
+  ssize_t srcLength = 0;             // length of serialized data chunk
+
+  // While srcLength is greater than zero
+  while ((srcLength = nghttp2_session_mem_send(session_, &src)) > 0) {
+    DEBUG_HTTP2("Nghttp2Session %s: nghttp2 has %d bytes to send\n",
+                TypeName(), srcLength);
+    size_t srcRemaining = srcLength;
+    size_t srcOffset = 0;
+
+    // The amount of data we have to copy is greater than the space
+    // remaining. Copy what we can into the remaining space, send it,
+    // the proceed with the rest.
+    while (srcRemaining > destRemaining) {
+      DEBUG_HTTP2("Nghttp2Session %s: pushing %d bytes to the socket\n",
+                  TypeName(), destRemaining);
+      memcpy(dest.base + destOffset, src + srcOffset, destRemaining);
+      destLength += destRemaining;
+      Send(&dest, destLength);
+      destOffset = 0;
+      destLength = 0;
+      srcRemaining -= destRemaining;
+      srcOffset += destRemaining;
+      destRemaining = dest.len;
+    }
+
+    if (srcRemaining > 0) {
+      memcpy(dest.base + destOffset, src + srcOffset, srcRemaining);
+      destLength += srcRemaining;
+      destOffset += srcRemaining;
+      destRemaining -= srcRemaining;
+      srcRemaining = 0;
+      srcOffset = 0;
     }
   }
+
+  if (destLength > 0) {
+    DEBUG_HTTP2("Nghttp2Session %s: pushing %d bytes to the socket\n",
+                TypeName(), destLength);
+    Send(&dest, destLength);
+  }
 }
 
 // Initialize the Nghttp2Session handle by creating and