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       mongoc_client_pool_t - mongoc_client_pool_t

       A connection pool for multi-threaded programs. See connection-pooling.


          typedef struct _mongoc_client_pool_t mongoc_client_pool_t

       mongoc_client_pool_t  is  the  basis  for  multi-threading  in the MongoDB C driver. Since
       mongoc_client_t structures are not thread-safe, this structure is used to retrieve  a  new
       mongoc_client_t  for  a  given  thread.  This  structure  is  thread-safe,  except for its
       destructor method, mongoc_client_pool_destroy, which is not thread-safe and must  only  be
       called from one thread.



          /* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
           * libmongoc-1.0) */

          /* ./example-pool [CONNECTION_STRING] */

          #include <mongoc/mongoc.h>
          #include <pthread.h>
          #include <stdio.h>

          static pthread_mutex_t mutex;
          static bool in_shutdown = false;

          static void *
          worker (void *data)
             mongoc_client_pool_t *pool = data;
             mongoc_client_t *client;
             bson_t ping = BSON_INITIALIZER;
             bson_error_t error;
             bool r;

             BSON_APPEND_INT32 (&ping, "ping", 1);

             while (true) {
                client = mongoc_client_pool_pop (pool);
                /* Do something with client. If you are writing an HTTP server, you
                 * probably only want to hold onto the client for the portion of the
                 * request performing database queries.
                r = mongoc_client_command_simple (
                   client, "admin", &ping, NULL, NULL, &error);

                if (!r) {
                   fprintf (stderr, "%s\n", error.message);

                mongoc_client_pool_push (pool, client);

                pthread_mutex_lock (&mutex);
                if (in_shutdown || !r) {
                   pthread_mutex_unlock (&mutex);

                pthread_mutex_unlock (&mutex);

             bson_destroy (&ping);
             return NULL;

          main (int argc, char *argv[])
             const char *uri_string = "mongodb://";
             mongoc_uri_t *uri;
             bson_error_t error;
             mongoc_client_pool_t *pool;
             pthread_t threads[10];
             unsigned i;
             void *ret;

             pthread_mutex_init (&mutex, NULL);
             mongoc_init ();

             if (argc > 1) {
                uri_string = argv[1];

             uri = mongoc_uri_new_with_error (uri_string, &error);
             if (!uri) {
                fprintf (stderr,
                         "failed to parse URI: %s\n"
                         "error message:       %s\n",
                return EXIT_FAILURE;

             pool = mongoc_client_pool_new (uri);
             mongoc_client_pool_set_error_api (pool, 2);

             for (i = 0; i < 10; i++) {
                pthread_create (&threads[i], NULL, worker, pool);

             sleep (10);
             pthread_mutex_lock (&mutex);
             in_shutdown = true;
             pthread_mutex_unlock (&mutex);

             for (i = 0; i < 10; i++) {
                pthread_join (threads[i], &ret);

             mongoc_client_pool_destroy (pool);
             mongoc_uri_destroy (uri);

             mongoc_cleanup ();

             return EXIT_SUCCESS;


       MongoDB, Inc


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