101 lines
3.9 KiB
Plaintext
101 lines
3.9 KiB
Plaintext
Multithreading
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==============
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Libnfs supports multithreading using the pthread API on linux/unix and using
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the native API for Windows.
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By default libnfs is beuilt without pthread support to avoid the overhead
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for locking, but pthread support, and thus support for multithreading, can be
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configured using --enable-pthread
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$ ./configure --prefix=/usr --enable-examples --enable-pthread
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It is not supported to mix the eventdriven ASYNC interface with multithreading
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thus once multithreading is enabled from the application you can not use
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the async interface any more and must only use the multithread safe
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SYNC API.
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The process to use multithreading from your application is:
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1, nfs_init_context() to create an NFS context. This context defaults to
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not (yet) be multithreading aware.
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2, nfs_mount(...) to mount the NFS share.
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IF the share mounted successfully we can now turn on multithreading for all I/O
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to the share:
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3, nfs_mt_service_thread_start(nfs)
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this starts a dedicated thread to manage all socket
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I/O and queue management and also flags the context
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to be multithreading ready.
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If this returns successfully you can now start using
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this context from separate threads in your
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application. But remember, only the SYNC API
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is supported from this point.
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... use the nfs context from all your threads ...
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Once the application is finished and ready to terminate, first close all other
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threads, or make sure that they will NOT perform any further I/O to the nfs
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context. Wait until all in-flight I/O has stopped.
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Then call nfs_mt_service_thread_stop(nfs) to terminate the service thread and
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disable the multithreading support.
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See examples/nfs-pthreads-example.c for an example utility that
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mounts a share, enables multithreading and then creates a number of worker
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threads that share the same nfs context.
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(In the example the threads just runs a busy loop calling nfs_stat64().)
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Porting
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-------
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The multithreading support is abstracted out into two separate files to make
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it easier to add other threading APIs instead of pthreads.
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include/libnfs-multithreading.h and lib/multithreading.c
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Multithreading requires two separate defines to be present.
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The global one is HAVE_MULTITHREADING which will activate general
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multithreading support in the library and the second one that enables a specific
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implementation of threading.
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HAVE_PTHREAD is defined when you want to use libpthread.
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For other threading APIs you will need a new define HAVE_OTHER_API
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to select it.
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include/libnfs-multithreading.h
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-------------------------------
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This file consists of two parts.
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The first part is creating typedefs for a tread, a mutex and a semaphore.
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When porting to a different threads API, add a new section that adds suitable
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typedefs for thread/mutex/semaphore.
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The second part is the wrapper API for the libnfs threading abstractions and
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should not need to be changed.
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lib/multithreading.c
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--------------------
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This file contains the actual abstraction used for multithreading.
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When porting to a different threads API you will need to create replacement
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functions for :
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nfs_mt_service_thread() : This is the service thread that is responsible
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for performing all socket I/O.
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nfs_mt_service_thread_start()
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nfs_mt_service_thread_stop()
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: Functions to start/stop the service thread.
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nfs_mt_mutex_init()
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nfs_mt_mutex_destroy()
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nfs_mt_mutex_lock()
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nfs_mt_mutex_unlock() : Wrappers that implement the 4 basic mutex calls.
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nfs_mt_sem_init()
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nfs_mt_sem_destroy()
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nfs_mt_sem_post()
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nfs_mt_sem_wait() : Wrappers that implement the 4 basic semaphore calls.
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nfs_mt_get_tid() : Get an identifier for the current thread.
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TODO
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----
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* Optimization: have the service thread just read the PDU from the socket and
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add it to a new queue. Then have a pool of threads to read from this queue and
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unmarshall the pdu's in concurrently.
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