Implicit Request Contexts
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Using Implicit Request Contexts
In addition to explicit and per-proxy request contexts, you can also establish an implicit context on a communicator. This implicit context is sent with all invocations made via proxies created by that communicator, provided that you do not supply an explicit context with the call.
Access to this implicit context is provided by the Communicator
interface:
module Ice { local interface Communicator { ImplicitContext getImplicitContext(); // ... }; };
getImplicitContext
returns the implicit context object. If a communicator has no implicit context, the operation returns null.
You can manipulate the contents of the implicit context via the ImplicitContext
interface:
local interface ImplicitContext { Context getContext(); void setContext(Context newContext); string get(string key); string put(string key, string value); string remove(string key); bool containsKey(string key); };
The getContext
operation returns the currently-set context dictionary. The setContext
operation replaces the currently-set context in its entirety.
The remaining operations allow you to manipulate specific entries:
get
This operation returns the value associated withkey
. Ifkey
was not previously set, the operation returns the empty string.
put
This operation adds the key-value pair specified bykey
andvalue
. It returns the previous value associated withkey
; if no value was previously associated withkey
, it returns the empty string. It is legal to add the empty string as a value.
remove
This operation removes the key-value pair specified bykey
. It returns the previously-set value (or the empty string ifkey
was not previously set).
containsKey
This operation returns true ifkey
is currently set and false, otherwise. You can use this operation to distinguish between a key-value pair that was explicitly added with an empty string as a value, and a key-value pair that was never added at all.
Scope of the Implicit Context
You establish the implicit context on a communicator by setting a property, Ice.ImplicitContext
. This property controls whether a communicator has an implicit context and, if so, at what scope the context applies. The property can be set to the following values:
None
With this setting (or ifIce.ImplicitContext
is not set at all), the communicator has no implicit context, andgetImplicitContext
returns null.
Shared
The communicator has a single implicit context that is shared by all threads. Access to the context via itsImplicitContext
interface is interlocked, so different threads can concurrently manipulate the context without risking data corruption or reading stale values.
PerThread
The communicator maintains a separate implicit context for each thread. This allows you to propagate contexts that depend on the sending thread (for example, to send per-thread transaction IDs).