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docs: update concurrency.md regarding thread creation

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Fixes #issue number 866

Signed-off-by: Jesse Grodman <jgrodman@gmail.com>
Change-Id: Ia102fbb285ef8914008d1a92347080953d394d2a
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/462878
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Chunyang Hui <chunyang.hui@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
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Jesse Grodman 2019-07-22 16:14:36 +03:00 committed by Changpeng Liu
parent a50246fb64
commit 53c9f4350a
1 changed files with 7 additions and 15 deletions
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doc/concurrency.md
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@ -71,15 +71,7 @@ basic message passing framework and defines a few key primitives.
First, spdk_thread is an abstraction for a thread of execution and First, spdk_thread is an abstraction for a thread of execution and
spdk_poller is an abstraction for a function that should be spdk_poller is an abstraction for a function that should be
periodically called on the given thread. On each system thread that the user periodically called on the given thread. On each system thread that the user
wishes to use with SPDK, they must first call spdk_allocate_thread(). This wishes to use with SPDK, they must first call spdk_thread_create().
function takes three function pointers - one that will be called to pass a
message to this thread, one that will be called to request that a poller be
started on this thread, and finally one to request that a poller be stopped.
*The implementation of these functions is not provided by this library*. Many
applications already have facilities for passing messages, so to ease
integration with existing code bases we've left the implementation up to the
user. However, for users starting from scratch, see the following section on
the event framework for an SPDK-provided implementation.
The library also defines two other abstractions: spdk_io_device and The library also defines two other abstractions: spdk_io_device and
spdk_io_channel. In the course of implementing SPDK we noticed the spdk_io_channel. In the course of implementing SPDK we noticed the
@ -105,7 +97,7 @@ all threads for which there is an io_channel for a given io_device.
As the number of example applications in SPDK grew, it became clear that a As the number of example applications in SPDK grew, it became clear that a
large portion of the code in each was implementing the basic message passing large portion of the code in each was implementing the basic message passing
infrastructure required to call spdk_allocate_thread(). This includes spawning infrastructure required to call spdk_thread_create(). This includes spawning
one thread per core, pinning each thread to a unique core, and allocating one thread per core, pinning each thread to a unique core, and allocating
lockless rings between the threads for message passing. Instead of lockless rings between the threads for message passing. Instead of
re-implementing that infrastructure for each example application, SPDK re-implementing that infrastructure for each example application, SPDK
@ -113,11 +105,11 @@ provides the SPDK @ref event. This library handles setting up all of the
message passing infrastructure, installing signal handlers to cleanly message passing infrastructure, installing signal handlers to cleanly
shutdown, implements periodic pollers, and does basic command line parsing. shutdown, implements periodic pollers, and does basic command line parsing.
When started through spdk_app_start(), the library automatically spawns all of When started through spdk_app_start(), the library automatically spawns all of
the threads requested, pins them, and calls spdk_allocate_thread() with the threads requested, pins them, and calls spdk_thread_create(). This makes
appropriate function pointers for each one. This makes it much easier to it much easier to implement a brand new SPDK application and is the recommended
implement a brand new SPDK application and is the recommended method for those method for those starting out. Only established applications with sufficient
starting out. Only established applications with sufficient message passing message passing infrastructure should consider directly integrating the lower
infrastructure should consider directly integrating the lower level libraries. level libraries.
# Limitations of the C Language # Limitations of the C Language