The first step in creating our C++ application is to compile our Slice definition to generate C++ proxies and skeletons. Under Unix, you can compile the definition as follows:
The slice2cpp compiler produces two C++ source files from this definition,
Printer.h and
Printer.cpp.
The Printer.h header file contains 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.cpp 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.cpp file must be compiled and linked into both client and server.
#include <Ice/Ice.h>
#include <Printer.h>
using namespace std;
using namespace Demo;
class PrinterI : public Printer {
public:
virtual void printString(const string& s,
const Ice::Current&);
};
void
PrinterI::
printString(const string& s, const Ice::Current&)
{
cout << s << endl;
}
int
main(int argc, char* argv[])
{
int status = 0;
Ice::CommunicatorPtr ic;
try {
ic = Ice::initialize(argc, argv);
Ice::ObjectAdapterPtr adapter
= ic‑>createObjectAdapterWithEndpoints(
"SimplePrinterAdapter", "default ‑p 10000");
Ice::ObjectPtr object = new PrinterI;
adapter‑>add(object,
ic‑>stringToIdentity("SimplePrinter"));
adapter‑>activate();
ic‑>waitForShutdown();
} catch (const Ice::Exception& e) {
cerr << e << endl;
status = 1;
} catch (const char* msg) {
cerr << msg << endl;
status = 1;
}
if (ic) {
try {
ic‑>destroy();
} catch (const Ice::Exception& e) {
cerr << e << endl;
status = 1;
}
}
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 C++ definitions for our printer interface, and we import the contents of the
std and
Demo namespaces for brevity in the code that follows:
#include <Ice/Ice.h>
#include <Printer.h>
using namespace std;
using namespace Demo;
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):
namespace Demo {
class Printer : virtual public Ice::Object {
public:
virtual void printString(const std::string&,
const Ice::Current&
= Ice::Current()
) = 0;
};
};
The Printer skeleton class definition is generated by the Slice compiler. (Note that the
printString method is pure virtual so the skeleton class cannot be instantiated.) Our servant class inherits from the skeleton class to provide an implementation of the pure virtual
printString method. (By convention, we use an
I‑suffix to indicate that the class implements an interface.)
class PrinterI : public Printer {
public:
virtual void printString(const string& s,
const Ice::Current&);
};
The implementation of the printString method is trivial: it simply writes its string argument to
stdout:
void
PrinterI::
printString(const string& s, const Ice::Current&)
{
cout << s << endl;
}
Note that printString has a second parameter of type
Ice::Current. As you can see from the definition of
Printer::printString, the Slice compiler generates a default argument for this parameter, so we can leave it unused in our implementation. (We will examine the purpose of the
Ice::Current parameter in
Section 32.6.)
int
main(int argc, char* argv[])
{
int status = 0;
Ice::CommunicatorPtr ic;
try {
// Server implementation here...
} catch (const Ice::Exception& e) {
cerr << e << endl;
status = 1;
} catch (const char* msg) {
cerr << msg << endl;
status = 1;
}
if (ic) {
try {
ic‑>destroy();
} catch (const Ice::Exception& e) {
cerr << e << endl;
status = 1;
}
}
return status;
}
The body of main contains the declaration of two variables,
status and
ic. The
status variable contains the exit status of the program and the
ic variable, of type
Ice::CommunicatorPtr, 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 two
catch handlers. The first handler catches all exceptions that may be thrown by the Ice run time; the intent is that, if the code encounters an unexpected Ice run-time exception anywhere, the stack is unwound all the way back to
main, which prints the exception and then returns failure to the operating system. The second handler catches string constants; the intent is that, if we encounter a fatal error condition somewhere in our code, we can simply throw a string literal with an error message. Again, this unwinds the stack all the way back to
main, which prints the error message and then returns failure to the operating system.
Following the try block, we see a bit of cleanup code that calls the
destroy method on the communicator (provided that the communicator was initialized). 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:
ic = Ice::initialize(argc, argv);
Ice::ObjectAdapterPtr adapter
= ic‑>createObjectAdapterWithEndpoints(
"SimplePrinterAdapter", "default ‑p 10000");
Ice::ObjectPtr object = new PrinterI;
adapter‑>add(object, ic‑>stringToIdentity("SimplePrinter"));
adapter‑>activate();
ic‑>waitForShutdown();
1. We initialize the Ice run time by calling Ice::initialize. (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
initialize returns a smart 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. (Ice ships with such a helper class, called
Ice::Application—see
Section 8.3.1.) As far as actual application code is concerned, the server contains only a few lines: six lines for the definition of the
PrinterI class, plus three
2 lines to instantiate a
PrinterI object and register it with the object adapter.
$ c++ ‑I. ‑I$ICE_HOME/include ‑c Printer.cpp Server.cpp
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 (such as an include directive for the STLport headers, or to control template instantiation); please see the demo programs that ship with Ice for the details.
$ c++ ‑o server Printer.o Server.o \
‑L$ICE_HOME/lib ‑lIce ‑lIceUtil
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. The important point to note here is that the Ice run time is shipped in two libraries,
libIce and
libIceUtil.
#include <Ice/Ice.h>
#include <Printer.h>
using namespace std;
using namespace Demo;
int
main(int argc, char* argv[])
{
int status = 0;
Ice::CommunicatorPtr ic;
try {
ic = Ice::initialize(argc, argv);
Ice::ObjectPrx base = ic‑>stringToProxy(
"SimplePrinter:default ‑p 10000");
PrinterPrx printer = PrinterPrx::checkedCast(base);
if (!printer)
throw "Invalid proxy";
printer‑>printString("Hello World!");
} catch (const Ice::Exception& ex) {
cerr << ex << endl;
status = 1;
} catch (const char* msg) {
cerr << msg << endl;
status = 1;
}
if (ic)
ic‑>destroy();
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
Ice::ObjectPrx, 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
PrinterPrx::checkedCast. 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.
$ c++ ‑I. ‑I$ICE_HOME/include ‑c Printer.cpp Client.cpp
$ c++ ‑o client Printer.o Client.o ‑L$ICE_HOME/lib ‑lIce ‑lIceUtil
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. (We will see cleaner ways to terminate a server in
Section 8.3.1.)
Note that, to successfully run client and server, you will have to set some platform-dependent environment variables. For example, under Linux, you need to add the Ice library directory to your
LD_LIBRARY_PATH. Please have a look at the demo applications that ship with Ice for the details for your platform.
