SQLite

static int doWalCallbacks(sqlite3 *db){
  int rc = SQLITE_OK;
#ifndef SQLITE_OMIT_WAL
  int i;
  for(i=0; i<db->nDb; i++){
    Btree *pBt = db->aDb[i].pBt;
    if( pBt ){
      int nEntry;
      sqlite3BtreeEnter(pBt);
      nEntry = sqlite3PagerWalCallback(sqlite3BtreePager(pBt));
      sqlite3BtreeLeave(pBt);
      if( db->xWalCallback && nEntry>0 && rc==SQLITE_OK ){
        rc = db->xWalCallback(db->pWalArg, db, db->aDb[i].zName, nEntry);
      }
    }
  }
#endif
  return rc;

** This file implements a simple standalone program used to stress the
** SQLite library when accessing the same set of databases simultaneously
** from multiple threads in shared-cache mode.
**
** This test program runs on unix-like systems only.  It uses pthreads.
** To compile:
**
**     gcc -g -Wall -I. threadtest4.c sqlite3.c -ldl -lpthread
**
** To run:
**
**     ./a.out 10
**
** The argument is the number of threads.  There are also options, such
** as -wal and -multithread and -serialized.
**
** Consider also compiling with clang instead of gcc and adding the
** -fsanitize=thread option.
*/
#include "sqlite3.h"
#include <pthread.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdarg.h>

/*
** An instance of the following structure is passed into each worker
** thread.
*/
typedef struct WorkerInfo WorkerInfo;
struct WorkerInfo {
  int tid;                    /* Thread ID */
  int nWorker;                /* Total number of workers */
  unsigned wkrFlags;          /* Flags */
  sqlite3 *mainDb;            /* Database connection of the main thread */
  sqlite3 *db;                /* Database connection of this thread */
  int nErr;                   /* Number of errors seen by this thread */
  int nTest;                  /* Number of tests run by this thread */
  char *zMsg;                 /* Message returned by this thread */
  pthread_t id;               /* Thread id */

  WorkerInfo *p = (WorkerInfo*)pArg;
  int iOuter;
  int i;
  int rc;
  sqlite3_stmt *pStmt;

  printf("worker %d startup\n", p->tid);  fflush(stdout);
  for(iOuter=1; iOuter<=p->nWorker; iOuter++){
    worker_open_connection(p, iOuter);
    for(i=0; i<4; i++){
      worker_add_content(p, i*100+1, (i+1)*100, (p->tid+iOuter)%3 + 1);
      worker_add_content(p, i*100+1, (i+1)*100, (p->tid+iOuter+1)%3 + 1);
      worker_add_content(p, i*100+1, (i+1)*100, (p->tid+iOuter+2)%3 + 1);
    }

    pStmt = prep_sql(p->db, "SELECT count(a) FROM t1 WHERE tid=%d", p->tid);
    worker_trace(p, "query [%s]", sqlite3_sql(pStmt));
    rc = sqlite3_step(pStmt);
    if( rc!=SQLITE_ROW ){
      worker_error(p, "Failed to step: %s", sqlite3_sql(pStmt));
    }else if( sqlite3_column_int(pStmt, 0)!=400 ){
      worker_error(p, "Wrong result: %d", sqlite3_column_int(pStmt,0));
    }
    if( p->nErr ) break;
    sqlite3_finalize(pStmt);

    if( ((iOuter+p->tid)%3)==0 ){
      sqlite3_db_release_memory(p->db);
      p->nTest++;
    }

    if( iOuter==p->tid ){
      pthread_mutex_lock(p->pWrMutex);
      run_sql(p, "VACUUM");
      pthread_mutex_unlock(p->pWrMutex);
    }

    worker_delete_all_content(p, (p->tid+iOuter)%2);
    worker_close_connection(p);
    p->db = 0;
  }
  worker_close_connection(p);
  printf("worker %d finished\n", p->tid); fflush(stdout);

  if( nWorker==0 ){ 
    fprintf(stderr,
       "usage:  %s ?OPTIONS? N\n"
       "N is the number of threads and must be at least 2.\n"
       "Options:\n"
       "  --serialized\n"
       "  --multithread\n"
       "  --wal\n"
       "  --trace\n"
       ,argv[0]
    );
    exit(1);
  }
  if( !sqlite3_threadsafe() ){
    fprintf(stderr, "requires a threadsafe build of SQLite\n");
    exit(1);

  run_sql(p, "CREATE TABLE IF NOT EXISTS test3.t3(tid INTEGER, sp, x, y, z)");
  run_sql(p, "CREATE INDEX test3.t3tid ON t3(tid)");
  run_sql(p, "CREATE INDEX test3.t3xy ON t3(x,y)");
  aInfo = safe_malloc( sizeof(*aInfo)*nWorker );
  memset(aInfo, 0, sizeof(*aInfo)*nWorker);
  for(i=0; i<nWorker; i++){
    aInfo[i].tid = i+1;
    aInfo[i].nWorker = nWorker;
    aInfo[i].wkrFlags = wkrFlags;
    aInfo[i].mainDb = db;
    aInfo[i].pWrMutex = &wrMutex;
    rc = pthread_create(&aInfo[i].id, 0, worker_thread, &aInfo[i]);
    if( rc!=0 ){
      fprintf(stderr, "thread creation failed for thread %d\n", i+1);
      exit(1);