/* impl.c.lockw3: RECURSIVE LOCKS IN WIN32
 *
 * $Id$
 * Copyright (c) 2001 Ravenbrook Limited.
 *
 * .design: These are implemented using critical sections.
 *  See the section titled "Synchronization functions" in the Groups
 *  chapter of the Microsoft Win32 API Programmer's Reference.
 *  The "Synchronization" section of the Overview is also relevant.
 *
 *  Critical sections support recursive locking, so the implementation
 *  could be trivial.  This implementation counts the claims to provide
 *  extra checking.
 *
 *  The limit on the number of recursive claims is the max of
 *  ULONG_MAX and the limit imposed by critical sections, which
 *  is believed to be about UCHAR_MAX.
 *
 *  During use the claims field is updated to remember the number of
 *  claims acquired on a lock.  This field must only be modified
 *  while we are inside the critical section.
 */

#include "mpm.h"

#ifndef MPS_OS_W3
#error "lockw3.c is specific to Win32 but MPS_OS_W3 not defined"
#endif

#include "mpswin.h"

SRCID(lockw3, "$Id$");


/* .lock.win32: Win32 lock structure; uses CRITICAL_SECTION */
typedef struct LockStruct {
  Sig sig;                      /* design.mps.sig */
  unsigned long claims;         /* # claims held by the owning thread */
  CRITICAL_SECTION cs;          /* Win32's recursive lock thing */
} LockStruct;


size_t LockSize(void)
{
  return sizeof(LockStruct);
}

Bool LockCheck(Lock lock)
{
  CHECKS(Lock, lock);
  return TRUE;
}

void LockInit(Lock lock)
{
  AVER(lock != NULL);
  lock->claims = 0;
  InitializeCriticalSection(&lock->cs);
  lock->sig = LockSig;
  AVERT(Lock, lock);
}

void LockFinish(Lock lock)
{
  AVERT(Lock, lock);
  /* Lock should not be finished while held */
  AVER(lock->claims == 0);
  DeleteCriticalSection(&lock->cs);
  lock->sig = SigInvalid;
}

void LockClaim(Lock lock)
{
  AVERT(Lock, lock);
  EnterCriticalSection(&lock->cs);
  /* This should be the first claim.  Now we are inside the
   * critical section it is ok to check this. */
  AVER(lock->claims == 0);
  lock->claims = 1;
}

void LockReleaseMPM(Lock lock)
{
  AVERT(Lock, lock);
  AVER(lock->claims == 1);  /* The lock should only be held once */
  lock->claims = 0;  /* Must set this before leaving CS */
  LeaveCriticalSection(&lock->cs);
}

void LockClaimRecursive(Lock lock)
{
  AVERT(Lock, lock);
  EnterCriticalSection(&lock->cs);
  ++lock->claims;
  AVER(lock->claims > 0);
}

void LockReleaseRecursive(Lock lock)
{
  AVERT(Lock, lock);
  AVER(lock->claims > 0);
  --lock->claims;
  LeaveCriticalSection(&lock->cs);
}



/* Global locking is performed by normal locks.
 * A separate lock structure is used for recursive and
 * non-recursive locks so that each may be differently ordered
 * with respect to client-allocated locks.
 */

static LockStruct globalLockStruct;
static LockStruct globalRecLockStruct;
static Lock globalLock = &globalLockStruct;
static Lock globalRecLock = &globalRecLockStruct;
static Bool globalLockInit = FALSE; /* TRUE iff initialized */


static void lockEnsureGlobalLock(void)
{
  /* Ensure both global locks have been initialized. */
  /* There is a race condition initializing them. */
  if (!globalLockInit) {
    LockInit(globalLock);
    LockInit(globalRecLock);
    globalLockInit = TRUE;
  }
}

void LockClaimGlobalRecursive(void)
{
  lockEnsureGlobalLock();
  AVER(globalLockInit);
  LockClaimRecursive(globalRecLock);
}

void LockReleaseGlobalRecursive(void)
{
  AVER(globalLockInit);
  LockReleaseRecursive(globalRecLock);
}

void LockClaimGlobal(void)
{
  lockEnsureGlobalLock();
  AVER(globalLockInit);
  LockClaim(globalLock);
}

void LockReleaseGlobal(void)
{
  AVER(globalLockInit);
  LockReleaseMPM(globalLock);
}