sqlite实现sqlite3_status接口

This module implements the sqlite3_status() interface and related
functionality.
*/
#include "sqliteInt.h"
#include "vdbeInt.h"

/*
Variables in which to record status information.
*/

#if SQLITE_PTRSIZE>4
typedef sqlite3_int64 sqlite3StatValueType;
#else
typedef u32 sqlite3StatValueType;
#endif
typedef struct sqlite3StatType sqlite3StatType;
static SQLITE_WSD struct sqlite3StatType {
  sqlite3StatValueType nowValue[10];  /* Current value */
  sqlite3StatValueType mxValue[10];   /* Maximum value */
} sqlite3Stat = { {0,}, {0,} };

/*
Elements of sqlite3Stat[] are protected by either the memory allocator
mutex, or by the pcache1 mutex.  The following array determines which.
*/

sqlite3Stat数组中的元素要么被内存分配器中的互斥变量保护，要么被pcache1中的互斥变量保护。值为1的被pcache1中的互斥变量保护，值为0的被内存分配器中的互斥变量保护

static const char statMutex[] = {
  0,  /* SQLITE_STATUS_MEMORY_USED */ memory_used
  1,  /* SQLITE_STATUS_PAGECACHE_USED */  pagecache_used
  1,  /* SQLITE_STATUS_PAGECACHE_OVERFLOW */  pagecache_overflow
  0,  /* SQLITE_STATUS_SCRATCH_USED */  scratch_used
  0,  /* SQLITE_STATUS_SCRATCH_OVERFLOW */  scratch_overflow
  0,  /* SQLITE_STATUS_MALLOC_SIZE */  malloc_size
  0,  /* SQLITE_STATUS_PARSER_STACK */  parser_stack
  1,  /* SQLITE_STATUS_PAGECACHE_SIZE */  pagecache_size
  0,  /* SQLITE_STATUS_SCRATCH_SIZE */  scratch_size
  0,  /* SQLITE_STATUS_MALLOC_COUNT */  malloc_count
};

/* The "wsdStat" macro will resolve to the status information
state vector.  If writable static data is unsupported on the target,
we have to locate the state vector at run-time.  In the more common
case where writable static data is supported, wsdStat can refer directly
to the "sqlite3Stat" state vector declared above.
*/

wsdStat宏会处理状态数组的状态信息。如果WSD不被支持，那么就需要在运行时分配堆栈。在一般情况下WSD是被支持的，这时可以直接通过sqlite3Stat来访问上面的状态数组

#ifdef SQLITE_OMIT_WSD
# define wsdStatInit  sqlite3StatType *x = &GLOBAL(sqlite3StatType,sqlite3Stat)
# define wsdStat x[0]
#else
# define wsdStatInit
# define wsdStat sqlite3Stat
#endif

/*
Return the current value of a status parameter.  The caller must
be holding the appropriate mutex.
*/

返回参数op代表的那个参数的状态值。判断的时候需要首先获得对应的互斥变量

sqlite3_int64 sqlite3StatusValue(int op){
  wsdStatInit;
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  return wsdStat.nowValue[op];
}

/*
Add N to the value of a status record.  The caller must hold the
appropriate mutex.  (Locking is checked by assert()).

The StatusUp() routine can accept positive or negative values for N.
The value of N is added to the current status value and the high-water
mark is adjusted if necessary.

The StatusDown() routine lowers the current value by N.  The highwater
mark is unchanged.  N must be non-negative for StatusDown().
*/

给状态值+N，调用者需要获得对应的互斥变量(在assert中检查锁)。

void sqlite3StatusUp(int op, int N){//N可正可负
  wsdStatInit;
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  wsdStat.nowValue[op] += N;
  if( wsdStat.nowValue[op]>wsdStat.mxValue[op] ){
    wsdStat.mxValue[op] = wsdStat.nowValue[op];//更新最大值
  }
}
void sqlite3StatusDown(int op, int N){//N必须>=0
  wsdStatInit;
  assert( N>=0 );
  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;
}

/*
Adjust the highwater mark if necessary.
The caller must hold the appropriate mutex.
*/

如果需要，就对highwater mark进行调整

void sqlite3StatusHighwater(int op, int X){
  sqlite3StatValueType newValue;
  wsdStatInit;
  assert( X>=0 );
  newValue = (sqlite3StatValueType)X;
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  assert( op==SQLITE_STATUS_MALLOC_SIZE
          || op==SQLITE_STATUS_PAGECACHE_SIZE
          || op==SQLITE_STATUS_PARSER_STACK );
  if( newValue>wsdStat.mxValue[op] ){
    wsdStat.mxValue[op] = newValue;//调整highwater mark
  }
}