Sockets

Bottleneck scenarios

Each scenario sets the throttles below and continues from the tick on screen.

Save and share

Note or question, saved in the file

The file holds the whole run and the step on screen, so whoever opens it can step back and forth from there. You can also drop a file onto the page.

Throttles

Sender thread

Work before each message

Network

Bandwidth

Latency (one way)

Max segment size (MSS)

Header per packet

Receiver thread

Work after each read

read() buffer size

You can also click a thread or the cable in the drawing, or press S, N or R, to pause or resume it.

Messages

Text to write

Each word becomes one write() call, ending in a newline ↵. Max 16 characters per word.

Keep writing random messages

Random message length

Socket and protocol

Send buffer (SO_SNDBUF)

Receive buffer (SO_RCVBUF)

Application code

The sender writes each message

One char is one byte. The buffer size and how the sender writes apply from the current tick.

Send buffer frees a byte

Changing the buffer sizes, the application code or the ACK rule restarts the connection and replays the same number of ticks.

Display

Each step shows

Time per step 0.8 s

Zoom 100%

Totals so far

Tick: 0
Written: 0
On wire: 0
Read: 0

write()s: 0
read()s: 0

1 msg: 0
Partial: 0
Mixed: 0

The first row counts bytes, the second system calls. A read() is “1 msg” only if it returned exactly one whole message.

Byte colour = the message it belongs to Thread running Blocked / zero window Paused · ACK Waiting for work Segment in flight Packet header (with sequence number) Bytes in focus Message boundary inside one read()

Where is the bottleneck?

Sender: each write() call

Receiver: what each read() returned

Events around this tick