Apple Darwin Manuel d'utilisateur télécharger pdf (Page 52)

the writepos must not be allowed to overtake the read

position, so subtract one from the final value.

#define BYTES_TO_WRITE(ringbuffer) (ringbuffer->readpos - \

ringbuffer->writepos + \

((ringbuffer->writepos >= ringbuffer->readpos) * \

ringbuffer->buflen) - 1)

The code reading from this buffer knows that it can always read from readpos forwards up to writepos (or

if writepos is less than readpos, it can read to the end of the buffer, then read from the start of the buffer

up to writepos). After reading, the read code updates readpos to reflect the location of the last byte read.

In a similar fashion, the code writing to this buffer knows that it can safely write from the writepos position

until it reaches readpos, wrapping around the end of the buffer if necessary. After writing, the write code

updates writepos to reflect the location of the last byte written.

Because only one process will ever modify either readpos or writepos, no synchronization between the two

processes is required. Note, however, that the reading code must protect readpos against other threads

within that process, and the writing code must do the same for writepos.

Launching the Helper Host

After you’ve build a helper host, the next step is to determine the architecture of the plug-in. For PEF/CFM

plug-ins, it is safe for you to assume that the plug-in contains 32-bit PowerPC executable code. For Mach-O

plug-ins, the method you should use varies according to the version of OS X being used.

For backward compatibility with versions of OS X prior to 10.5, your application should use the detection code

presented in the CheckExecutableArchitecture sample code. This sample code is straightforward and presents

a fairly easy way to determine which architecture to use for loading existing plug-ins.

In OS X v10.5 and later, you should use the CFBundle API. This API is safer as a long-term solution, because it

will support any binary format that is supported by that particular version of OS X, thus freeing you from the

need to alter the code as new binary formats are introduced. The relevant functions are:

CFArrayRef CFBundleCopyExecutableArchitecturesForURL(CFURLRef url);

CFArrayRef CFBundleCopyExecutableArchitectures(CFBundleRef bundle);

Cross-Architecture Plug-in Support

Launching the Helper Host

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Apple Darwin Manuel d'utilisateur Page 52