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Seastar

Introduction

SeaStar is an event-driven framework allowing you to write non-blocking, asynchronous code in a relatively straightforward manner (once understood). Its APIs are based on futures.

Seastar utilizes the following concepts to achieve extreme performance:

• Cooperative micro-task scheduler: instead of running threads, each core runs a cooperative task scheduler. Each task is typically very lightweight -- only running for as long as it takes to process the last I/O operation's result and to submit a new one.
• Share-nothing SMP architecture: each cores run independently of other cores in an SMP system. Memory, data structures, and CPU time are not shared; instead, inter-core communication uses explicit message passing. A seastar core is often termed a shard.
• Future based APIs: futures allow you to submit an I/O operation and to chain tasks to be executed on completion of the I/O operation. It is easy to run multiple I/O operations in parallel - for example, in response to a request coming from a TCP connection, you can issue multiple disk I/O requests, send messages to other cores on the same system, or send requests to other nodes in the cluster, wait for some or all of the results to complete, aggregate the results, and send a response.
• Share-nothing TCP stack: while seastar can use the host operating system's TCP stack, it also provides its own high-performance TCP/IP stack built on top of the task scheduler and the share-nothing architecture. The stack provides zero-copy in both directions: you can process data directly from the TCP stack's buffers, and send the contents of your own data structures as part of a message without incurring a copy. Read mode...
• DMA-based storage APIs: as with the networking stack, seastar provides zero-copy storage APIs, allowing you to DMA your data to and from your storage devices.

Building

See Building Seastar and Running unit tests.

Writing seastar code

See the Tutorial or look at the Sample applications.