ref: 86e0099835f99de6ccc3bee33a297387993aa037
dir: /sys/src/libc/arm/lock.c/
#include <u.h> #include <libc.h> static long lockinit(long); /* * barrier is called from atom.s and tas.s assembly * to execute memory barrier. */ long (*_barrier)(long) = lockinit; static int cpus(void) { char buf[256], *p; int f, n; f = open("#c/sysstat", OREAD); if(f < 0) return -1; n = read(f, buf, sizeof(buf)-1); close(f); if(n <= 0) return -1; buf[n] = '\0'; n = 0; p = buf; while(*p != '\0'){ if(*p == '\n') n++; p++; } return n; } long _dmb(long); static long _nop(long r0) { return r0; } static long lockinit(long r0) { if(cpus() > 1) _barrier = _dmb; else _barrier = _nop; return (*_barrier)(r0); } void lock(Lock *lk) { int i; /* once fast */ if(!_tas(&lk->val)) return; /* a thousand times pretty fast */ for(i=0; i<1000; i++){ if(!_tas(&lk->val)) return; sleep(0); } /* now nice and slow */ for(i=0; i<1000; i++){ if(!_tas(&lk->val)) return; sleep(100); } /* take your time */ while(_tas(&lk->val)) sleep(1000); } int canlock(Lock *lk) { return _tas(&lk->val) == 0; } void unlock(Lock *lk) { lk->val = (*_barrier)(0); }