The first step in creating our Objective‑C application is to compile our Slice definition to generate Objective‑C proxies and skeletons. Under Unix, you can compile the definition as follows:
The slice2objc compiler produces two Objective‑C source files from this definition,
Printer.h and
Printer.m.
The Printer.h header file contains Objective‑C type definitions that correspond to the Slice definitions for our
Printer interface. This header file must be included in both the client and the server source code.
The Printer.m file contains the source code for our
Printer interface. The generated source contains type-specific run-time support for both clients and servers. For example, it contains code that marshals parameter data (the string passed to the
printString operation) on the client side and unmarshals that data on the server side.
The Printer.m file must be compiled and linked into both client and server.
#import <Ice/Ice.h>
#import <Printer.h>
#import <Foundation/NSAutoreleasePool.h>
#import <stdio.h>
@interface PrinterI : DemoPrinter <DemoPrinter>
@end
@implementation PrinterI
‑(void) printString:(NSMutableString *)s
current:(ICECurrent *)current
{
printf("%s\n", [s UTF8String]);
}
@end
int
main(int argc, char* argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int status = 1;
id<ICECommunicator> communicator = nil;
@try {
communicator =
[ICEUtil createCommunicator:&argc argv:argv];
id<ICEObjectAdapter> adapter =
[communicator createObjectAdapterWithEndpoints:
@"SimplePrinterAdapter"
endpoints:@"default ‑p 10000"];
ICEObject *object = [[[PrinterI alloc] init] autorelease];
[adapter add:object identity:[communicator
stringToIdentity:@"SimplePrinter"]];
[adapter activate];
[communicator waitForShutdown];
status = 0;
} @catch (NSException* ex) {
NSLog(@"%@", ex);
}
@try {
[communicator destroy];
} @catch (NSException* ex) {
NSLog(@"%@", ex);
}
[pool release];
return status;
}
There appears to be a lot of code here for something as simple as a server that just prints a string. Do not be concerned by this: most of the preceding code is boiler plate that never changes. For this very simple server, the code is dominated by this boiler plate.
Every Ice source file starts with an include directive for Ice.h, which contains the definitions for the Ice run time. We also include
Printer.h, which was generated by the Slice compiler and contains the Objective‑C definitions for our printer interface. We also import headers to allow us to use an autorelease pool and to produce output:
#import <Ice/Ice.h>
#import <Printer.h>
#import <Foundation/NSAutoreleasePool.h>
#import <stdio.h>
Our server implements a single printer servant, of type PrinterI. Looking at the generated code in
Printer.h, we find the following (tidied up a little to get rid of irrelevant detail):
@protocol DemoPrinter <ICEObject>
‑(void) printString:(NSMutableString *)s
current:(ICECurrent *)current;
@end
@interface DemoPrinter : ICEObject
// ...
@end
The DemoPrinter protocol and class definitions are generated by the Slice compiler. The protocol defines the
printString method, which we must implement in our servant. The
DemoPrinter class contains methods that are internal to the mapping, so we are not concerned with these. However, our servant must derive from this skeleton class:
@interface PrinterI : DemoPrinter <DemoPrinter>
@end
@implementation PrinterI
‑(void) printString:(NSMutableString *)s
current:(ICECurrent *)current
{
printf("%s\n", [s UTF8String]);
}
@end
As you can see, the implementation of the printString method is trivial: it simply writes its string argument to
stdout.
Note that printString has a second parameter of type
ICECurrent. The Ice run time passes additional information about an incoming request to the servant in this parameter. For now, we will ignore it. (See
Section 32.6 for more information about this parameter.)
int
main(int argc, char* argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int status = 1;
id<ICECommunicator> communicator = nil;
@try {
communicator =
[ICEUtil createCommunicator:&argc argv:argv];
// Server implementation here...
status = 0;
} @catch (NSException* ex) {
NSLog(@"%@", ex);
}
@try {
[communicator destroy];
} @catch (NSException* ex) {
NSLog(@"%@", ex);
}
[pool release];
return status;
}
The body of main instantiates an autorelease pool, which it releases before returning to ensure that the program does not leak memory.
main contains the declaration of two variables,
status and
communicator. The
status variable contains the exit status of the program and the
communicator variable, of type
id<ICECommunicator>, contains the main handle to the Ice run time.
Following these declarations is a try block in which we place all the server code, followed by a
catch handler that logs any unhandled exceptions.
Before returning, main executes a bit of cleanup code that calls the
destroy method on the communicator. The cleanup call is outside the first
try block for a reason: we must ensure that the Ice run time is finalized whether the code terminates normally or terminates due to an exception.
1
The body of the first try block contains the actual server code:
communicator =
[ICEUtil createCommunicator:&argc argv:argv];
id<ICEObjectAdapter> adapter =
[communicator createObjectAdapterWithEndpoints:
@"SimplePrinterAdapter"
endpoints:@"default ‑p 10000"];
ICEObject *object = [[[PrinterI alloc] init] autorelease];
[adapter add:object identity:[communicator
stringToIdentity:@"SimplePrinter"]];
[adapter activate];
[communicator waitForShutdown];
1. We initialize the Ice run time by calling createCommunicator. (We pass
argc and
argv to this call because the server may have command-line arguments that are of interest to the run time; for this example, the server does not require any command-line arguments.) The call to
createCommunicator returns a pointer to an
Ice::Communicator object, which is the main handle to the Ice run time.
2.
We create an object adapter by calling createObjectAdapterWithEndpoints on the
Communicator instance. The arguments we pass are
"SimplePrinterAdapter" (which is the name of the adapter) and
"default ‑p 10000", which instructs the adapter to listen for incoming requests using the default protocol (TCP/IP) at port number 10000.
4.
We inform the object adapter of the presence of a new servant by calling add on the adapter; the arguments to
add are the servant we have just instantiated, plus an identifier. In this case, the string
"SimplePrinter" is the name of the servant. (If we had multiple printers, each would have a different name or, more correctly, a different
object identity.)
5.
Next, we activate the adapter by calling its activate method. (The adapter is initially created in a holding state; this is useful if we have many servants that share the same adapter and do not want requests to be processed until after all the servants have been instantiated.) The server starts to process incoming requests from clients as soon as the adapter is activated.
6.
Finally, we call waitForShutdown. This call suspends the calling thread until the server implementation terminates, either by making a call to shut down the run time, or in response to a signal. (For now, we will simply interrupt the server on the command line when we no longer need it.)
Note that, even though there is quite a bit of code here, that code is essentially the same for all servers. You can put that code into a helper class and, thereafter, will not have to bother with it again. As far as actual application code is concerned, the server contains only a few lines: nine lines for the definition of the
PrinterI class, plus three
2 lines to instantiate a
PrinterI object and register it with the object adapter.
$ cc -c -I. -I$ICE_HOME/include Printer.m Server.m
This compiles both our application code and the code that was generated by the Slice compiler. We assume that the
ICE_HOME environment variable is set to the top-level directory containing the Ice run time. (For example, if you have installed Ice in
/opt/Ice, set
ICE_HOME to that path.) Depending on your platform, you may have to add additional include directives or other options to the compiler; please see the demo programs that ship with Ice for the details.
$ c++ Printer.o Server.o -o server \
-L$ICE_HOME/lib -lIceObjC -framework Foundation
Again, depending on the platform, the actual list of libraries you need to link against may be longer. The demo programs that ship with Ice contain all the detail.
#import <Ice/Ice.h>
#import <Printer.h>
#import <Foundation/NSAutoreleasePool.h>
#import <stdio.h>
int
main(int argc, char* argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
int status = 1;
id<ICECommunicator> communicator = nil;
@try {
communicator =
[ICEUtil createCommunicator:&argc argv:argv];
id<ICEObjectPrx> base = [communicator
stringToProxy:@"SimplePrinter:default ‑p 10000"];
id<DemoPrinterPrx> printer =
[DemoPrinterPrx checkedCast:base];
if(!printer)
[NSException raise:@"Invalid proxy" format:nil];
[printer printString:@"Hello World!"];
status = 0;
} @catch (NSException* ex) {
NSLog(@"%@", ex);
}
@try {
[communicator destroy];
} @catch (NSException* ex) {
NSLog(@"%@", ex);
}
[pool release];
return status;
}
Note that the overall code layout is the same as for the server: we include the headers for the Ice run time and the header generated by the Slice compiler, and we use the same
try block and
catch handlers to deal with errors.
The code in the try block does the following:
2.
The next step is to obtain a proxy for the remote printer. We create a proxy by calling
stringToProxy on the communicator, with the string
"SimplePrinter:default ‑p 10000". Note that the string contains the object identity and the port number that were used by the server. (Obviously, hard-coding object identities and port numbers into our applications is a bad idea, but it will do for now; we will see more architecturally sound ways of doing this in
Chapter 38.)
3.
The proxy returned by stringToProxy is of type
id<ICEObjectPrx>, which is at the root of the inheritance tree for interfaces and classes. But to actually talk to our printer, we need a proxy for a
Printer interface, not an
Object interface. To do this, we need to do a down-cast by calling the
checkedCast class method on the
DemoPrinterPrx class. A checked cast sends a message to the server, effectively asking “is this a proxy for a
Printer interface?” If so, the call returns a proxy to a
Printer; otherwise, if the proxy denotes an interface of some other type, the call returns a null proxy.
$ cc -c -I. -I$ICE_HOME/include Printer.m Client.m
$ c++ Printer.o Client.o -o client \
-L$ICE_HOME/lib -lIceObjC -framework Foundation
The client runs and exits without producing any output; however, in the server window, we see the
"Hello World!" that is produced by the printer. To get rid of the server, we interrupt it on the command line for now.
Note that, to successfully run client and server, you may have to set DYLD_LIBRARY_PATH to include the Ice library directory. Please see the installation instructions and the demo applications that ship with Ice Touch for details.
