Provided by: libmongoc-doc_1.26.0-1.1ubuntu2_all 
INSTALLING
For detailed instructions on installing the MongoDB C Driver on a particular platform,
please see the installation guide.
STARTING MONGODB
To run the examples in this tutorial, MongoDB must be installed and running on localhost
on the default port, 27017. To check if it is up and running, connect to it with the
MongoDB shell.
$ mongosh --host localhost --port 27017 --quiet
Enterprise rs0 [direct: primary] test> db.version()
7.0.0
>
INCLUDE AND LINK LIBMONGOC IN YOUR C PROGRAM
Include mongoc.h
All libmongoc's functions and types are available in one header file. Simply include
mongoc/mongoc.h:
#include <mongoc/mongoc.h>
CMake
The libmongoc installation includes a CMake config-file package, so you can use CMake's
find_package command to import libmongoc's CMake target and link to libmongoc (as a shared
library):
CMakeLists.txt
# Specify the minimum version you require.
find_package (mongoc-1.0 1.7 REQUIRED)
# The "hello_mongoc.c" sample program is shared among four tests.
add_executable (hello_mongoc ../../hello_mongoc.c)
target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_shared)
You can also use libmongoc as a static library instead: Use the mongo::mongoc_static CMake
target:
# Specify the minimum version you require.
find_package (mongoc-1.0 1.7 REQUIRED)
# The "hello_mongoc.c" sample program is shared among four tests.
add_executable (hello_mongoc ../../hello_mongoc.c)
target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_static)
pkg-config
If you're not using CMake, use pkg-config on the command line to set header and library
paths:
gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-1.0)
Or to statically link to libmongoc:
gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-static-1.0)
Specifying header and include paths manually
If you aren't using CMake or pkg-config, paths and libraries can be managed manually.
$ gcc -o hello_mongoc hello_mongoc.c \
-I/usr/local/include/libbson-1.0 -I/usr/local/include/libmongoc-1.0 \
-lmongoc-1.0 -lbson-1.0
$ ./hello_mongoc
{ "ok" : 1.000000 }
For Windows users, the code can be compiled and run with the following commands. (This
assumes that the MongoDB C Driver has been installed to C:\mongo-c-driver; change the
include directory as needed.)
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 hello_mongoc.c
C:\> hello_mongoc
{ "ok" : 1.000000 }
USE LIBMONGOC IN A MICROSOFT VISUAL STUDIO PROJECT
See the libmongoc and Visual Studio guide.
MAKING A CONNECTION
Access MongoDB with a mongoc_client_t. It transparently connects to standalone servers,
replica sets and sharded clusters on demand. To perform operations on a database or
collection, create a mongoc_database_t or mongoc_collection_t struct from the
mongoc_client_t.
At the start of an application, call mongoc_init() before any other libmongoc functions.
At the end, call the appropriate destroy function for each collection, database, or client
handle, in reverse order from how they were constructed. Call mongoc_cleanup() before
exiting.
The example below establishes a connection to a standalone server on localhost, registers
the client application as "connect-example," and performs a simple command.
More information about database operations can be found in the CRUD Operations and
Executing Commands sections. Examples of connecting to replica sets and sharded clusters
can be found in the Advanced Connections page, while examples of data compression can be
found in the Data Compression page.
hello_mongoc.c
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
const char *uri_string = "mongodb://localhost:27017";
mongoc_uri_t *uri;
mongoc_client_t *client;
mongoc_database_t *database;
mongoc_collection_t *collection;
bson_t *command, reply, *insert;
bson_error_t error;
char *str;
bool retval;
/*
* Required to initialize libmongoc's internals
*/
mongoc_init ();
/*
* Optionally get MongoDB URI from command line
*/
if (argc > 1) {
uri_string = argv[1];
}
/*
* Safely create a MongoDB URI object from the given string
*/
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
/*
* Create a new client instance
*/
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
/*
* Register the application name so we can track it in the profile logs
* on the server. This can also be done from the URI (see other examples).
*/
mongoc_client_set_appname (client, "connect-example");
/*
* Get a handle on the database "db_name" and collection "coll_name"
*/
database = mongoc_client_get_database (client, "db_name");
collection = mongoc_client_get_collection (client, "db_name", "coll_name");
/*
* Do work. This example pings the database, prints the result as JSON and
* performs an insert
*/
command = BCON_NEW ("ping", BCON_INT32 (1));
retval = mongoc_client_command_simple (
client, "admin", command, NULL, &reply, &error);
if (!retval) {
fprintf (stderr, "%s\n", error.message);
return EXIT_FAILURE;
}
str = bson_as_json (&reply, NULL);
printf ("%s\n", str);
insert = BCON_NEW ("hello", BCON_UTF8 ("world"));
if (!mongoc_collection_insert_one (collection, insert, NULL, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
}
bson_destroy (insert);
bson_destroy (&reply);
bson_destroy (command);
bson_free (str);
/*
* Release our handles and clean up libmongoc
*/
mongoc_collection_destroy (collection);
mongoc_database_destroy (database);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
CREATING BSON DOCUMENTS
Documents are stored in MongoDB's data format, BSON. The C driver uses libbson to create
BSON documents. There are several ways to construct them: appending key-value pairs, using
BCON, or parsing JSON.
Appending BSON
A BSON document, represented as a bson_t in code, can be constructed one field at a time
using libbson's append functions.
For example, to create a document like this:
{
born : ISODate("1906-12-09"),
died : ISODate("1992-01-01"),
name : {
first : "Grace",
last : "Hopper"
},
languages : [ "MATH-MATIC", "FLOW-MATIC", "COBOL" ],
degrees: [ { degree: "BA", school: "Vassar" }, { degree: "PhD", school: "Yale" } ]
}
Use the following code:
#include <bson/bson.h>
int
main (int argc, char *argv[])
{
struct tm born = {0};
struct tm died = {0};
const char *lang_names[] = {"MATH-MATIC", "FLOW-MATIC", "COBOL"};
const char *schools[] = {"Vassar", "Yale"};
const char *degrees[] = {"BA", "PhD"};
uint32_t i;
bson_t *document;
bson_t child;
bson_array_builder_t *bab;
char *str;
document = bson_new ();
/*
* Append { "born" : ISODate("1906-12-09") } to the document.
* Passing -1 for the length argument tells libbson to calculate the
* string length.
*/
born.tm_year = 6; /* years are 1900-based */
born.tm_mon = 11; /* months are 0-based */
born.tm_mday = 9;
bson_append_date_time (document, "born", -1, mktime (&born) * 1000);
/*
* Append { "died" : ISODate("1992-01-01") } to the document.
*/
died.tm_year = 92;
died.tm_mon = 0;
died.tm_mday = 1;
/*
* For convenience, this macro passes length -1 by default.
*/
BSON_APPEND_DATE_TIME (document, "died", mktime (&died) * 1000);
/*
* Append a subdocument.
*/
BSON_APPEND_DOCUMENT_BEGIN (document, "name", &child);
BSON_APPEND_UTF8 (&child, "first", "Grace");
BSON_APPEND_UTF8 (&child, "last", "Hopper");
bson_append_document_end (document, &child);
/*
* Append array of strings. Generate keys "0", "1", "2".
*/
BSON_APPEND_ARRAY_BUILDER_BEGIN (document, "languages", &bab);
for (i = 0; i < sizeof lang_names / sizeof (char *); ++i) {
bson_array_builder_append_utf8 (bab, lang_names[i], -1);
}
bson_append_array_builder_end (document, bab);
/*
* Array of subdocuments:
* degrees: [ { degree: "BA", school: "Vassar" }, ... ]
*/
BSON_APPEND_ARRAY_BUILDER_BEGIN (document, "degrees", &bab);
for (i = 0; i < sizeof degrees / sizeof (char *); ++i) {
bson_array_builder_append_document_begin (bab, &child);
BSON_APPEND_UTF8 (&child, "degree", degrees[i]);
BSON_APPEND_UTF8 (&child, "school", schools[i]);
bson_array_builder_append_document_end (bab, &child);
}
bson_append_array_builder_end (document, bab);
/*
* Print the document as a JSON string.
*/
str = bson_as_canonical_extended_json (document, NULL);
printf ("%s\n", str);
bson_free (str);
/*
* Clean up allocated bson documents.
*/
bson_destroy (document);
return 0;
}
See the libbson documentation for all of the types that can be appended to a bson_t.
Using BCON
BSON C Object Notation, BCON for short, is an alternative way of constructing BSON
documents in a manner closer to the intended format. It has less type-safety than BSON's
append functions but results in less code.
#include <bson/bson.h>
int
main (int argc,
char *argv[])
{
struct tm born = { 0 };
struct tm died = { 0 };
bson_t *document;
char *str;
born.tm_year = 6;
born.tm_mon = 11;
born.tm_mday = 9;
died.tm_year = 92;
died.tm_mon = 0;
died.tm_mday = 1;
document = BCON_NEW (
"born", BCON_DATE_TIME (mktime (&born) * 1000),
"died", BCON_DATE_TIME (mktime (&died) * 1000),
"name", "{",
"first", BCON_UTF8 ("Grace"),
"last", BCON_UTF8 ("Hopper"),
"}",
"languages", "[",
BCON_UTF8 ("MATH-MATIC"),
BCON_UTF8 ("FLOW-MATIC"),
BCON_UTF8 ("COBOL"),
"]",
"degrees", "[",
"{", "degree", BCON_UTF8 ("BA"), "school", BCON_UTF8 ("Vassar"), "}",
"{", "degree", BCON_UTF8 ("PhD"), "school", BCON_UTF8 ("Yale"), "}",
"]");
/*
* Print the document as a JSON string.
*/
str = bson_as_canonical_extended_json (document, NULL);
printf ("%s\n", str);
bson_free (str);
/*
* Clean up allocated bson documents.
*/
bson_destroy (document);
return 0;
}
Notice that BCON can create arrays, subdocuments and arbitrary fields.
Creating BSON from JSON
For single documents, BSON can be created from JSON strings via bson_new_from_json.
#include <bson/bson.h>
int
main (int argc,
char *argv[])
{
bson_error_t error;
bson_t *bson;
char *string;
const char *json = "{\"name\": {\"first\":\"Grace\", \"last\":\"Hopper\"}}";
bson = bson_new_from_json ((const uint8_t *)json, -1, &error);
if (!bson) {
fprintf (stderr, "%s\n", error.message);
return EXIT_FAILURE;
}
string = bson_as_canonical_extended_json (bson, NULL);
printf ("%s\n", string);
bson_free (string);
return 0;
}
To initialize BSON from a sequence of JSON documents, use bson_json_reader_t.
BASIC CRUD OPERATIONS
This section demonstrates the basics of using the C Driver to interact with MongoDB.
Inserting a Document
To insert documents into a collection, first obtain a handle to a mongoc_collection_t via
a mongoc_client_t. Then, use mongoc_collection_insert_one() to add BSON documents to the
collection. This example inserts into the database "mydb" and collection "mycoll".
When finished, ensure that allocated structures are freed by using their respective
destroy functions.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc,
char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_oid_t oid;
bson_t *doc;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost:27017/?appname=insert-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
doc = bson_new ();
bson_oid_init (&oid, NULL);
BSON_APPEND_OID (doc, "_id", &oid);
BSON_APPEND_UTF8 (doc, "hello", "world");
if (!mongoc_collection_insert_one (
collection, doc, NULL, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
}
bson_destroy (doc);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o insert insert.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./insert
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 insert.c
C:\> insert
To verify that the insert succeeded, connect with the MongoDB shell.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find()
{ "_id" : ObjectId("55ef43766cb5f36a3bae6ee4"), "hello" : "world" }
>
Finding a Document
To query a MongoDB collection with the C driver, use the function
mongoc_collection_find_with_opts(). This returns a cursor to the matching documents. The
following examples iterate through the result cursors and print the matches to stdout as
JSON strings.
Use a document as a query specifier; for example,
{ "color" : "red" }
will match any document with a field named "color" with value "red". An empty document {}
can be used to match all documents.
This first example uses an empty query specifier to find all documents in the database
"mydb" and collection "mycoll".
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_t *query;
char *str;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=find-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
query = bson_new ();
cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
C:\> find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
To look for a specific document, add a specifier to query. This example adds a call to
BSON_APPEND_UTF8() to look for all documents matching {"hello" : "world"}.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_t *query;
char *str;
mongoc_init ();
client = mongoc_client_new (
"mongodb://localhost:27017/?appname=find-specific-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
query = bson_new ();
BSON_APPEND_UTF8 (query, "hello", "world");
cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
$ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
C:\> find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
Updating a Document
This code snippet gives an example of using mongoc_collection_update_one() to update the
fields of a document.
Using the "mydb" database, the following example inserts an example document into the
"mycoll" collection. Then, using its _id field, the document is updated with different
values and a new field.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_collection_t *collection;
mongoc_client_t *client;
bson_error_t error;
bson_oid_t oid;
bson_t *doc = NULL;
bson_t *update = NULL;
bson_t *query = NULL;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=update-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
bson_oid_init (&oid, NULL);
doc = BCON_NEW ("_id", BCON_OID (&oid), "key", BCON_UTF8 ("old_value"));
if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
goto fail;
}
query = BCON_NEW ("_id", BCON_OID (&oid));
update = BCON_NEW ("$set",
"{",
"key",
BCON_UTF8 ("new_value"),
"updated",
BCON_BOOL (true),
"}");
if (!mongoc_collection_update_one (
collection, query, update, NULL, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
goto fail;
}
fail:
if (doc)
bson_destroy (doc);
if (query)
bson_destroy (query);
if (update)
bson_destroy (update);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o update update.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./update
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 update.c
C:\> update
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
To verify that the update succeeded, connect with the MongoDB shell.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find({"updated" : true})
{ "_id" : ObjectId("55ef549236fe322f9490e17b"), "updated" : true, "key" : "new_value" }
>
Deleting a Document
This example illustrates the use of mongoc_collection_delete_one() to delete a document.
The following code inserts a sample document into the database "mydb" and collection
"mycoll". Then, it deletes all documents matching {"hello" : "world"}.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_oid_t oid;
bson_t *doc;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=delete-example");
collection = mongoc_client_get_collection (client, "test", "test");
doc = bson_new ();
bson_oid_init (&oid, NULL);
BSON_APPEND_OID (doc, "_id", &oid);
BSON_APPEND_UTF8 (doc, "hello", "world");
if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
fprintf (stderr, "Insert failed: %s\n", error.message);
}
bson_destroy (doc);
doc = bson_new ();
BSON_APPEND_OID (doc, "_id", &oid);
if (!mongoc_collection_delete_one (
collection, doc, NULL, NULL, &error)) {
fprintf (stderr, "Delete failed: %s\n", error.message);
}
bson_destroy (doc);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o delete delete.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./delete
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 delete.c
C:\> delete
Use the MongoDB shell to prove that the documents have been removed successfully.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.count({"hello" : "world"})
0
>
Counting Documents
Counting the number of documents in a MongoDB collection is similar to performing a find
operation. This example counts the number of documents matching {"hello" : "world"} in the
database "mydb" and collection "mycoll".
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_t *doc;
int64_t count;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=count-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
doc = bson_new_from_json (
(const uint8_t *) "{\"hello\" : \"world\"}", -1, &error);
count = mongoc_collection_count (
collection, MONGOC_QUERY_NONE, doc, 0, 0, NULL, &error);
if (count < 0) {
fprintf (stderr, "%s\n", error.message);
} else {
printf ("%" PRId64 "\n", count);
}
bson_destroy (doc);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o count count.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./count
1
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 count.c
C:\> count
1
EXECUTING COMMANDS
The driver provides helper functions for executing MongoDB commands on client, database
and collection structures. The _simple variants return booleans indicating success or
failure.
This example executes the ping command against the database "mydb".
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
bson_error_t error;
bson_t *command;
bson_t reply;
char *str;
mongoc_init ();
client = mongoc_client_new (
"mongodb://localhost:27017/?appname=executing-example");
command = BCON_NEW ("ping", BCON_INT32 (1));
if (mongoc_client_command_simple (
client, "mydb", command, NULL, &reply, &error)) {
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (stderr, "Failed to run command: %s\n", error.message);
}
bson_destroy (command);
bson_destroy (&reply);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o executing executing.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./executing
{ "ok" : { "$numberDouble" : "1.0" }, "$clusterTime" : { "clusterTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } }, "signature" : { "hash" : { "$binary" : { "base64" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=", "subType" : "00" } }, "keyId" : { "$numberLong" : "0" } } }, "operationTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } } }
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 executing.c
C:\> executing
{ "ok" : { "$numberDouble" : "1.0" }, "$clusterTime" : { "clusterTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } }, "signature" : { "hash" : { "$binary" : { "base64" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=", "subType" : "00" } }, "keyId" : { "$numberLong" : "0" } } }, "operationTime" : { "$timestamp" : { "t" : 1682609211, "i" : 1 } } }
THREADING
The MongoDB C Driver is thread-unaware in the vast majority of its operations. This means
it is up to the programmer to guarantee thread-safety.
However, mongoc_client_pool_t is thread-safe and is used to fetch a mongoc_client_t in a
thread-safe manner. After retrieving a client from the pool, the client structure should
be considered owned by the calling thread. When the thread is finished, the client should
be placed back into the pool.
example-pool.c
/* 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);
break;
}
pthread_mutex_unlock (&mutex);
}
bson_destroy (&ping);
return NULL;
}
int
main (int argc, char *argv[])
{
const char *uri_string = "mongodb://127.0.0.1/?appname=pool-example";
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",
uri_string,
error.message);
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;
}
NEXT STEPS
To find information on advanced topics, browse the rest of the C driver guide or the
official MongoDB documentation.
For help with common issues, consult the Troubleshooting page. To report a bug or request
a new feature, follow these instructions.
AUTHOR
MongoDB, Inc
COPYRIGHT
2017-present, MongoDB, Inc