mirror of https://github.com/grpc/grpc-go.git
56 lines
2.0 KiB
Markdown
56 lines
2.0 KiB
Markdown
# Flow Control
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Flow control is a feature in gRPC that prevents senders from writing more data
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on a stream than a receiver is capable of handling. This feature behaves the
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same for both clients and servers. Because gRPC-Go uses a blocking-style API
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for stream operations, flow control pushback is implemented by simply blocking
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send operations on a stream when that stream's flow control limits have been
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reached. When the receiver has read enough data from the stream, the send
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operation will unblock automatically. Flow control is configured automatically
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based on a connection's Bandwidth Delay Product (BDP) to ensure the buffer is
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the minimum size necessary to allow for maximum throughput on the stream if the
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receiver is reading at its maximum speed.
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## Try it
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```
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go run ./server
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```
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```
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go run ./client
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```
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## Example explanation
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The example client and server are written to demonstrate the blocking by
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intentionally sending messages while the other side is not receiving. The
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bidirectional echo stream in the example begins by having the client send
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messages until it detects it has blocked (utilizing another goroutine). The
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server sleeps for 2 seconds to allow this to occur. Then the server will read
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all of these messages, and the roles of the client and server are swapped so the
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server attempts to send continuously while the client sleeps. After the client
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sleeps for 2 seconds, it will read again to unblock the server. The server will
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detect that it has blocked, and end the stream once it has unblocked.
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### Expected Output
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The client output should look like:
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```
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2023/09/19 15:49:49 New stream began.
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2023/09/19 15:49:50 Sending is blocked.
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2023/09/19 15:49:51 Sent 25 messages.
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2023/09/19 15:49:53 Read 25 messages.
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2023/09/19 15:49:53 Stream ended successfully.
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```
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while the server should output the following logs:
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```
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2023/09/19 15:49:49 New stream began.
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2023/09/19 15:49:51 Read 25 messages.
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2023/09/19 15:49:52 Sending is blocked.
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2023/09/19 15:49:53 Sent 25 messages.
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2023/09/19 15:49:53 Stream ended successfully.
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```
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