[lwip-devel] [bug #20842] unix sys_arch_protect faulty

[Thomas Taranowski]

Update of bug #20842 (project lwip):

                Severity:              3 - Normal => 2 - Minor              

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Follow-up Comment #7:

My sys_arch differs slightly from the unix, and I don't have a unix test bed,
so I'm putting what I got, which should be readily translatable to the unix
version...  

Note that each function that  contains a critical section declares a single
static semaphore that's local to the function.  With this method the critical
section is function-local, rather than system-wide, which appears to be the
correct semantics, given the code that is current using it.

In sys_arch.h
--------------
#define SYS_ARCH_DECL_PROTECT(lev)  static sys_sem_t localsem =
(sys_sem_t)0xffffffff; static unsigned protct=0; static thread_handle_t
protthread=(thread_handle_t)0xffffffff; if(localsem==(sys_sem_t)0xffffffff)
localsem=sys_sem_new(1);


#define SYS_ARCH_PROTECT(lev) sys_arch_protect(localsem, &protct,
&protthread)

#define SYS_ARCH_UNPROTECT(lev) sys_arch_unprotect(localsem, &protct,
&protthread)

In sys_arch.c
-------------
sys_prot_t sys_arch_protect(sys_sem_t localsem, unsigned *protct,
thread_handle_t *protthread)
{
  
  if(protthread!=currentThreadHandle()) {
    //We have a new thread that wants to lock some critical session.  Wait
until it gets it.
    sys_arch_sem_wait(localsem,0);
    *protthread = currentThreadHandle();
    *protct=1;
  } else {
    //The thread handle matches, so this thread already has it locked!Bump
the count
    (*protct)++;    
  }
  

  return 0;
}
void sys_arch_unprotect(sys_sem_t localsem, unsigned *protct, thread_handle_t
*protthread)
{
  LWIP_ASSERT("sys_arch_unprotect: Not the current critical section
locker.",
    *protthread==currentThreadHandle());

  //I have it locked, unprotecting
  (*protct)--;
  if(*protct==0) {
    //reset the thread id
    *protthread=0xffffffff;
    //release the semaphore
    sys_sem_signal(localsem);
  }




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