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46 строки
2.4 KiB
ReStructuredText
46 строки
2.4 KiB
ReStructuredText
Optimizing applications for NSPR
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NetScape Portable Runtime (NSPR) tries to provide a consistent level of
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service across the platforms it supports. This has proven to be quite
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challenging, a challenge that was met to a large degree, but there is
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always room for improvement. The casual client may not encounter a need
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to know the details of the shortcomings to the level described here, but
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if and when clients become more sophisticated, these issues will
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certainly surface.
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*This memo is by no way complete.*
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Multiplatform
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-------------
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- Do not call any blocking system call from a local thread. The only
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exception to this rule is the <tt>select()</tt> and <tt>poll()</tt>
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system calls on Unix, both of which NSPR has overridden to make sure
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they are aware of the NSPR local threads.
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- In the combined (MxN) model, which includes NT, IRIX (sprocs), and
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pthreads-user, the primordial thread is always a local thread.
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Therefore, if you call a blocking system call from the primordial
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thread, it is going to block more than just the primordial thread and
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the system may not function correctly. On NT, this problem is
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especially obvious because the idle thread, which is in charge of
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driving the asynch io completion port, is also blocked. Do not call
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blocking system calls from the primordial thread. Create a global
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thread and call the system call in that thread, and have the
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primordial thread join that thread.
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- NSPR uses timer signals to implement thread preemption for local
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threads on some platforms. If all the software linked into the
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application is not ported to the NSPR API, the application may fail
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because of threads being preempted during critical sections. To
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disable thread preemption call
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<tt>PR_DisableClockInterrupts()</tt>during initialization.
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- Interrupting threads (via <tt>PR_Interrupt()</tt>) on threads blocked
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in I/O functions is implemented to various degrees on different
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platforms. The UNIX based platforms all implement the function though
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there may be up to a 5 second delay in processing the request.
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- The mechanism used to implement <tt>PR_Interrupt()</tt> on the
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*pthreads* versions of NSPR is flawed. No failure attributable to the
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flaw has shown up in any tests or products - yet. The specific area
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surrounding pthread's *continuation thread* has been both observed
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and empirically proven faulty, and a correction identified.
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