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Subject: Re: "spinlock" API
From: Michael Davidsaver <mdavidsaver@bnl.gov>
To: Andrew Johnson <anj@aps.anl.gov>
Cc: core-talk@aps.anl.gov
Date: Mon, 11 Jun 2012 16:22:48 -0400
On 6/11/2012 12:06 PM, Andrew Johnson wrote:
On 2012-06-11 Michael Davidsaver wrote:
I used 'unsigned long' in the example, but the formal specification
would be:

typedef<unspecified>  epicsSpinKey;
Unfortunately the header does have to fully define the key type, since the
user code has to instantiate one of these to be able to take a lock.

By unspecified I mean only that the type aliased to epicsSpinKey is not part of the API and users should consider that it may change.

#define epicsSLLocalFlag(name) epicsSLFlag name = 0
...
It's quite valid to call a function to initialize something one of its
arguments points at; we do that all the time with calls to sscanf() for
example without it generating warnings.  I don't think the macro is necessary.

Sorry, wrong warning...  You are correct that the '=0' isn't needed

When I firsted implemented this with macros I was getting "usused variable" warnings so I wanted a way to make the flag variable disappear when not needed.

The current implementation for the thread pool:

#if defined(vxWorks) || defined(__rtems__)
#include "epicsInterrupt.h"
#define POOLFLAG(flag) int flag

#define LOCKPOOL(pP, pFlag) do{ *(pFlag) = epicsInterruptLock(); }while(0)

#define UNLOCKPOOL(pP, pFlag) do{ epicsInterruptUnlock(*(pFlag)); }while(0)

#else
#include "epicsMutex.h"
#define POOLFLAG(flag) do{}while(0)

#define LOCKPOOL(pP, pFlag) epicsMutexMustLock((pP)->guard)

#define UNLOCKPOOL(pP, pFlag) epicsMutexUnlock((pP)->guard)

#define POOLUSEMUTEX 1

#endif

where POOLUSEMUTEX  is used like

#ifdef POOLUSEMUTEX
    epicsMutexId guard;
#endif

A better thing to do might be

#if defined(vxWorks) || defined(__rtems__)
typedef void* epicsSpinId
#else
typedef epicsMutexID* epicsSpinId
#endif

I have a revised preference about names, to match other OSI APIs:

typedef struct epicsSpin * epicsSpinId;

Then replace all instances of epicsSpin * with epicsSpinId.

Ok.


Michael


Replies:
Re: "spinlock" API Andrew Johnson
References:
"spinlock" API Michael Davidsaver
Re: "spinlock" API Andrew Johnson
Re: "spinlock" API Michael Davidsaver
Re: "spinlock" API Andrew Johnson

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