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Usage
=====
`yc`
----
`yc` is a memcached/yrmcds client program. It provides access to all
libyrmcds library functions therefore access to all server functions.
`yc` prints out its usage when invoked without command-line arguments.
Minimal example
---------------
```c
#include <yrmcds.h>
#include <errno.h>
#include <error.h>
#include <stdlib.h>
#include <stdio.h>
void check_error(yrmcds_error e) {
if( e != 0 ) {
if( e == YRMCDS_SYSTEM_ERROR ) {
error(0, errno, "system error");
} else {
fprintf(stderr, "yrmcds error: %s\n", yrmcds_strerror(e));
}
exit(2);
}
}
void check_response(const yrmcds_response* r) {
if( r->status != YRMCDS_STATUS_OK ) {
fprintf(stderr, "Command failed: 0x%04x %.*s\n",
r->status, (int)r->data_len, r->data);
exit(3);
}
}
int main(int argc, char** argv) {
yrmcds c;
yrmcds_response r;
check_error( yrmcds_connect(&c, "localhost", 11211) );
check_error( yrmcds_noop(&c, NULL) );
check_error( yrmcds_recv(&c, &r) );
check_response(&r);
check_error( yrmcds_close(&c) );
return 0;
}
```
Compilation and linking
-----------------------
Link with `-lyrmcds -lpthread` as follows:
```
gcc -g -O2 -o foo foo.c -lyrmcds -lpthread
```
Request serial number
---------------------
All command sending functions can issue a unique serial number of the
command. This can be used when you receive responses asynchronously
as described in the next section.
```c
uint32_t async_cas(yrmcds* c) {
uint32_t serial;
// try compare-and-swap
check_error( yrmcds_set(&c, "abc", 3, "12345", 5, 0, 0, 5, 0, &serial) );
return serial;
}
```
Multi-threading
---------------
All functions in libyrmcds are thread-safe as long as different `yrmcds`
structs are used. Additionally, any number of threads can use command
sending functions such as `yrmcds_get()` or `yrmcds_set()` even when
they share the same `yrmcds` struct.
Further, `yrmcds_recv()` can be used in parallel with command sending
functions. You can create a dedicated thread to receive server responses
asynchronously. Use request serial numbers to identify a response's
request.
```c
void async_recv(yrmcds* c, void (*notify)(uint32_t, yrmcds_response* r)) {
yrmcds_respone r;
while( 1 ) {
check_error( yrmcds_recv(&c, &r) );
(*notify)(r.serial, &r);
}
}
```
You can use `yrmcds_shutdown()` to interrupt the thread blocking in
`yrmcds_recv()` for graceful exit.
Transparent compression
-----------------------
libyrmcds provides optional transparent data compression by [LZ4][].
To use this feature, the library must be built with LZ4 as follows:
```
$ make lz4
$ make
```
If the library supports LZ4 compression, you can enable transparent
LZ4 (de)compression for large objects. The threshold for compression
can be set by `yrmcds_set_compression()`. The compression is disabled
by default.
Note that all clients must support and enable the compression to
properly handle compressed data.
Text protocol support
---------------------
Although libyrmcds is designed for binary protocol, yet it provides
limited access to text protocol commands. Use `yrmcds_text_mode()`
to put the connection into the text protocol mode:
```c
check_error( yrmcds_connect(&c, "localhost", 11211) );
check_error( yrmcds_text_mode(&c) );
// Use the library API just in the same way as binary protocol.
```
Limitations:
* Only subset of commands can be used.
`yrmcds_get_touch`, lock related functions, `yrmcds_incr2` and
`yrmcds_decr2`, stat functions, key dump extension are not supported.
* Quiet mutation cannot be used.
`quiet` arguments must be 0. You need to receive a response for
every command.
* `yrmcds_response::cas_unique` is always 0 for storage commands.
The response for `yrmcds_set`, `yrmcds_add`, or `yrmcds_replace`
will not bring the correct CAS value. Use `yrmcds_get` or
`yrmcds_getk` to retrieve the correct value.
* `yrmcds_response::command` value is dummy.
Because `command` is one of binary protocol command numbers.
Counter extension
-----------------
yrmcds has a distributed counter extension for resource management.
If the extension is enabled in server, you can access counters by `yrmcds_cnt_*` functions.
The usage of each function is very similar to the corresponding `yrmcds_` function.
The minimum example is:
```c
#include <yrmcds.h>
#include <errno.h>
#include <error.h>
#include <stdio.h>
#include <stdlib.h>
void check_error(yrmcds_error e) {
if( e != YRMCDS_OK ) {
if( e == YRMCDS_SYSTEM_ERROR ) {
error(0, errno, "system error");
} else {
fprintf(stderr, "yrmcds error: %s\n", yrmcds_strerror(e));
}
exit(2);
}
}
void check_response(const yrmcds_cnt_response* r) {
if( r->status != YRMCDS_STATUS_OK ) {
fprintf(stderr, "Command failed: 0x%02x %.*s\n",
r->status, (int)r->body_length, r->body);
exit(3);
}
}
int main(void) {
yrmcds_cnt c;
yrmcds_cnt_response r;
check_error( yrmcds_cnt_connect(&c, "localhost", 11215) );
check_error( yrmcds_cnt_noop(&c, NULL) );
check_error( yrmcds_cnt_recv(&c, &r) );
check_response(&r);
check_error( yrmcds_cnt_close(&c) );
return 0;
}
```
API documents
-------------
HTML documents generated with Doxygen is available [here][api].
[api]: http://cybozu.github.io/libyrmcds/html/
[LZ4]: https://code.google.com/p/lz4/
|
