Question

I have a C++ program in which I have multiple threads writing into my SQLite tables(WAL mode is enabled) of a single database. Each thread creates a SQLite handle, does a sqlite3_open(), writes into the tables(there writes are with in a transaction) and then does a sqlite3_close(), and then SQLite handles are deleted. Then the thread dies.

Even after all the threads die, SQLite handles are still open. Why are not SQLite handles getting closed? What am I missing here?

My C++ program is running on a CentOS 5.5.

[Edit]
Here is my sample program using pthread

void threadFunction(void* pArg) {
    sqlite3 *handle;
    sqlite3_open("a.cm", &handle);    
    printf("Worker thread - Opened \n");
    sleep(10);    
    int r = sqlite3_close(handle);
    printf("Ret: %d\n", r);
    printf("Worker thread - Closed \n");
}

int main() {
    int i(0);
    pthread_t thread1, thread2;
    printf("Creating a worker thread\n");
    printf("SQLite libversion: %s\n", sqlite3_libversion());
    sqlite3 *handle;
    sqlite3_open("a.cm", &handle);    
    sqlite3_exec(handle, "pragma journal_mode = WAL", NULL, NULL, NULL);    
    printf("Main thread - Opened \n");

    pthread_create(&thread1, NULL, threadFunction, NULL);
    pthread_create(&thread2, NULL, threadFunction, NULL);

    pthread_join( thread1, NULL);
    pthread_join( thread2, NULL);
    sleep(200);
    sqlite3_close(handle);
    printf("Main thread - close \n");
    return 0;
}

Answer 1

Contacted the SQLite team: Here is their reply-

When you close one connection (In WAL mode),
SQLite checks if any other connection in the process is holding
a POSIX lock on the database file being closed. If so, it defers
closing the file-handle until the other connection drops its
POSIX lock (the file descriptor will be reused if yet another
connection to the same file is opened, but otherwise it just
hangs around waiting until it can be safely closed).

The conclusion is:
So until the connection is closed from the main() function
the handles opened from the other threads will not be closed!