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Overview
Comment:Back out the use of __sync_fetch_and_sub() as it does not appear to work.
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SHA1: 4c2efd4239bf07eb4b92d4af54edd68ee6312670
User & Date: drh 2017-01-03 21:50:49.166
Context
2017-01-03
21:57
Use compiler intrinsic functions for signed integer math when overflow detection is needed. (check-in: d3ac32a6e7 user: drh tags: trunk)
21:50
Back out the use of __sync_fetch_and_sub() as it does not appear to work. (Closed-Leaf check-in: 4c2efd4239 user: drh tags: gnu-safe-math)
21:03
Fix a typo in a comment. (check-in: ae087123db user: drh tags: gnu-safe-math)
18:05
Use the GCC built-in __sync_fetch_and_sub() to make the sqlite3StatusDown() routine atomic, and thereby avoid some mutexing. (check-in: f69ce75b3d user: drh tags: gnu-safe-math)
Changes
Side-by-Side Diff Ignore Whitespace Patch
Changes to src/malloc.c.
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    }else{
      /* Release memory back to the heap */
      assert( sqlite3MemdebugHasType(p, MEMTYPE_SCRATCH) );
      assert( sqlite3MemdebugNoType(p, (u8)~MEMTYPE_SCRATCH) );
      sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
      if( sqlite3GlobalConfig.bMemstat ){
        int iSize = sqlite3MallocSize(p);
#ifndef SQLITE_ATOMIC_STATUS_DOWN
        sqlite3_mutex_enter(mem0.mutex);
#endif
        sqlite3StatusDown(SQLITE_STATUS_SCRATCH_OVERFLOW, iSize);
        sqlite3StatusDown(SQLITE_STATUS_MEMORY_USED, iSize);
        sqlite3StatusDown(SQLITE_STATUS_MALLOC_COUNT, 1);
        sqlite3GlobalConfig.m.xFree(p);
#ifndef SQLITE_ATOMIC_STATUS_DOWN
        sqlite3_mutex_leave(mem0.mutex);
#endif
      }else{
        sqlite3GlobalConfig.m.xFree(p);
      }
    }
  }
}
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** Free memory previously obtained from sqlite3Malloc().
*/
void sqlite3_free(void *p){
  if( p==0 ) return;  /* IMP: R-49053-54554 */
  assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
  assert( sqlite3MemdebugNoType(p, (u8)~MEMTYPE_HEAP) );
  if( sqlite3GlobalConfig.bMemstat ){
#ifndef SQLITE_ATOMIC_STATUS_DOWN
    sqlite3_mutex_enter(mem0.mutex);
#endif
    sqlite3StatusDown(SQLITE_STATUS_MEMORY_USED, sqlite3MallocSize(p));
    sqlite3StatusDown(SQLITE_STATUS_MALLOC_COUNT, 1);
    sqlite3GlobalConfig.m.xFree(p);
#ifndef SQLITE_ATOMIC_STATUS_DOWN
    sqlite3_mutex_leave(mem0.mutex);
#endif
  }else{
    sqlite3GlobalConfig.m.xFree(p);
  }
}

/*
** Add the size of memory allocation "p" to the count in
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Changes to src/sqliteInt.h.
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#  define SQLITE_NOINLINE  __attribute__((noinline))
#elif defined(_MSC_VER) && _MSC_VER>=1310
#  define SQLITE_NOINLINE  __declspec(noinline)
#else
#  define SQLITE_NOINLINE
#endif

/*
** The SQLITE_ATOMIC_STATUS_DOWN macro is defined if and only if
** the sqlite3StatusDown() function is threadsafe.
*/
#if !defined(SQLITE_DISABLE_INTRINSIC) \
    && (GCC_VERSION>=4004000 || CLANG_VERSION>=3000000)
# define SQLITE_ATOMIC_STATUS_DOWN 1
#endif

/*
** Make sure that the compiler intrinsics we desire are enabled when
** compiling with an appropriate version of MSVC unless prevented by
** the SQLITE_DISABLE_INTRINSIC define.
*/
#if !defined(SQLITE_DISABLE_INTRINSIC)
#  if defined(_MSC_VER) && _MSC_VER>=1400
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Changes to src/status.c.
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  if( wsdStat.nowValue[op]>wsdStat.mxValue[op] ){
    wsdStat.mxValue[op] = wsdStat.nowValue[op];
  }
}
void sqlite3StatusDown(int op, int N){
  wsdStatInit;
  assert( N>=0 );
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
#if !defined(SQLITE_DISABLE_INTRINSIC) \
    && (GCC_VERSION>=4004000 || CLANG_VERSION>=3000000)
  (void)__sync_fetch_and_sub(&wsdStat.nowValue[op], N);
#else
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  wsdStat.nowValue[op] -= N;
#endif
}

/*
** Adjust the highwater mark if necessary.
** The caller must hold the appropriate mutex.
*/
void sqlite3StatusHighwater(int op, int X){
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