semaphore.cpp

00001 /**
00002  * code from Igor Skochinsky
00003  * taken from http://mbed.org/forum/mbed/post/799/
00004 */
00005 
00006 #include "semaphore.h"
00007 
00008 Semaphore::Semaphore(): s(SemFree) {};
00009 bool Semaphore::_abort=false;
00010 
00011 bool Semaphore::take(bool block) {
00012     if (_abort)
00013         block=false;
00014     int oldval;
00015 /*    
00016 #if defined(TARGET_LPC1768) // on Cortex-M3 we can use ldrex/strex
00017     do {
00018         // read the semaphore value
00019         oldval = __ldrex(&s);
00020         // loop again if it is locked and we are blocking
00021         // or setting it with strex failed
00022     } while ( (block && oldval == SemTaken) || __strex(SemTaken, &s) != 0 );
00023     if ( !block ) __clrex(); // clear exclusive lock set by ldrex
00024 #else // on arm7 there's only swp
00025 
00026     do {
00027         // swp sets the pointed data to the given value and returns the previous one
00028         oldval = __swp(SemTaken, &s);
00029         // if blocking, loop until the previous value becomes 0
00030         // which would mean we have successfully taken the lock
00031     } while (block && oldval == SemTaken);
00032 //#endif
00033 
00034     return oldval == SemFree;
00035 */
00036 return true;    
00037 }
00038 
00039 // release the semaphore
00040 void Semaphore::release() {
00041     s = SemFree;
00042 }