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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:

{zcode:slice}
module Ice {
    local interface Communicator
    {
        ImplicitContext getImplicitContext();

        // ...
    };
};
{zcode}

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:

{zcode:slice}
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);
};
{zcode}

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 with key. If key was not previously set, the operation returns the empty string.

• put
  This operation adds the key-value pair specified by key and value. It returns the previous value associated with key; if no value was previously associated with key, 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 by key. It returns the previously-set value (or the empty string if key was not previously set).

• containsKey
  This operation returns true if key 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.

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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 if Ice.ImplicitContext is not set at all), the communicator has no implicit context, and getImplicitContext returns null.

• Shared
  The communicator has a single implicit context that is shared by all threads. Access to the context via its ImplicitContext 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).

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See Also

• Explicit Request Contexts
• Per-Proxy Request Contexts