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Specifies that each application ___domain of your managed application should have its own copy of a particular global variable or static member variable. See Application Domains and Visual C++ for more information.
Every application ___domain has its own copy of a per-appdomain variable. A constructor of an appdomain variable is executed when an assembly is loaded into an application ___domain, and the destructor is executed when the application ___domain is unloaded.
If you want all application domains within a process in the common language runtime to share a global variable, use the __declspec(process) modifier. __declspec(process) is in effect by default under /clr and __declspec(appdomain) is in effect by default under /clr:pure. __declspec(appdomain) is enforced under /clr:safe.
__declspec(appdomain) is only valid when one of the /clr compiler options is used. Only a global variable, static member variable, or a static local variable can be marked with __declspec(appdomain). It is an error to apply __declspec(appdomain) to static members of managed types because they always have this behavior.
Using __declspec(appdomain) is similar to using Thread Local Storage (TLS). Threads have their own storage, as do application domains. Using __declspec(appdomain) ensures the global variable has its own storage in each application ___domain created for this application.
There are limitations to mixing the use of per process and per appdomain variables; see process for more information.
For example, at program start up, all per-process variables are initialized, then all per-appdomain variables are initialized. Therefore when a per-process variable is being initialized, it cannot depend on the value of any per-application ___domain variable. It is bad practice to mix the use (assignment) of per appdomain and per process variables.
For information on how to call a function in a specific application ___domain, see call_in_appdomain Function.
Example
// declspec_appdomain.cpp
// compile with: /clr
#include <stdio.h>
using namespace System;
class CGlobal {
public:
CGlobal(bool bProcess) {
Counter = 10;
m_bProcess = bProcess;
Console::WriteLine("__declspec({0}) CGlobal::CGlobal constructor", m_bProcess ? (String^)"process" : (String^)"appdomain");
}
~CGlobal() {
Console::WriteLine("__declspec({0}) CGlobal::~CGlobal destructor", m_bProcess ? (String^)"process" : (String^)"appdomain");
}
int Counter;
private:
bool m_bProcess;
};
__declspec(process) CGlobal process_global = CGlobal(true);
__declspec(appdomain) CGlobal appdomain_global = CGlobal(false);
value class Functions {
public:
static void change() {
++appdomain_global.Counter;
}
static void display() {
Console::WriteLine("process_global value in appdomain '{0}': {1}",
AppDomain::CurrentDomain->FriendlyName,
process_global.Counter);
Console::WriteLine("appdomain_global value in appdomain '{0}': {1}",
AppDomain::CurrentDomain->FriendlyName,
appdomain_global.Counter);
}
};
int main() {
AppDomain^ defaultDomain = AppDomain::CurrentDomain;
AppDomain^ ___domain = AppDomain::CreateDomain("Domain 1");
AppDomain^ domain2 = AppDomain::CreateDomain("Domain 2");
CrossAppDomainDelegate^ changeDelegate = gcnew CrossAppDomainDelegate(&Functions::change);
CrossAppDomainDelegate^ displayDelegate = gcnew CrossAppDomainDelegate(&Functions::display);
// Print the initial values of appdomain_global in all appdomains.
Console::WriteLine("Initial value");
defaultDomain->DoCallBack(displayDelegate);
___domain->DoCallBack(displayDelegate);
domain2->DoCallBack(displayDelegate);
// Changing the value of appdomain_global in the ___domain and domain2
// appdomain_global value in "default" appdomain remain unchanged
process_global.Counter = 20;
___domain->DoCallBack(changeDelegate);
domain2->DoCallBack(changeDelegate);
domain2->DoCallBack(changeDelegate);
// Print values again
Console::WriteLine("Changed value");
defaultDomain->DoCallBack(displayDelegate);
___domain->DoCallBack(displayDelegate);
domain2->DoCallBack(displayDelegate);
AppDomain::Unload(___domain);
AppDomain::Unload(domain2);
}
__declspec(process) CGlobal::CGlobal constructor __declspec(appdomain) CGlobal::CGlobal constructor Initial value process_global value in appdomain 'declspec_appdomain.exe': 10 appdomain_global value in appdomain 'declspec_appdomain.exe': 10 __declspec(appdomain) CGlobal::CGlobal constructor process_global value in appdomain 'Domain 1': 10 appdomain_global value in appdomain 'Domain 1': 10 __declspec(appdomain) CGlobal::CGlobal constructor process_global value in appdomain 'Domain 2': 10 appdomain_global value in appdomain 'Domain 2': 10 Changed value process_global value in appdomain 'declspec_appdomain.exe': 20 appdomain_global value in appdomain 'declspec_appdomain.exe': 10 process_global value in appdomain 'Domain 1': 20 appdomain_global value in appdomain 'Domain 1': 11 process_global value in appdomain 'Domain 2': 20 appdomain_global value in appdomain 'Domain 2': 12 __declspec(appdomain) CGlobal::~CGlobal destructor __declspec(appdomain) CGlobal::~CGlobal destructor __declspec(appdomain) CGlobal::~CGlobal destructor __declspec(process) CGlobal::~CGlobal destructor