On some platforms such as Windows NT, Client-Library implements fully asynchronous network I/O by spawning internal worker threads to handle network I/O. When a fully asynchronous I/O is in effect on these platforms, an internal Client-Library thread waits for the completion of each I/O request, and invoke the application's completion callback. Before the operation completes, the thread may call other application callbacks. For example, if the server sends server messages, the internal Client-Library thread reads the messages and calls the application's server-message callback.In these situations, the callback code and the application's mainline code run in different threads. When coding a fully asynchronous application on a platform where Client-Library uses thread-driven I/O, you must make sure that the callbacks communicate properly with the mainline code. Table 2-22 summarizes which thread invokes each callback type.
Callback type |
Invocation thread |
|---|---|
CS-Library error handler |
The thread that provoked the error event. |
Client message |
When the CS_NETIO connection property is CS_DEFER_IO or CS_SYNC_IO, the callback is invoked from the thread that provoked the error.On thread-driven I/O platforms, when the CS_NETIO connection property is CS_ASYNC_IO, the callback can be invoked from a Client-Library worker thread or the thread that provoked the error event, depending on when the error is discovered. |
Completion |
When the CS_NETIO connection property is CS_DEFER_IO, the callback is invoked from the thread that calls ct_poll.On thread-driven I/O platforms, when the CS_NETIO connection property is CS_ASYNC_IO, the callback is invoked from a Client-Library worker thread. |
Directory |
When the CS_NETIO connection property is CS_SYNC_IO or CS_DEFER_IO, the callback is invoked from the thread that called ct_ds_lookup.On thread-driven I/O platforms, when the CS_NETIO connection property is CS_ASYNC_IO, the callback is invoked from an internal Client-Library thread. |
Encryption, negotiation, or security session |
When the CS_NETIO connection property is CS_SYNC_IO or CS_DEFER_IO, the callback is invoked from the thread that called ct_connect.On thread-driven I/O platforms, when the CS_NETIO connection property is CS_ASYNC_IO, the callback is invoked from an internal Client-Library thread. |
Notification |
When the CS_ASYNC_NOTIFS property is CS_FALSE (the default), the callback is invoked from the thread that was reading from the network at the time the notification arrived.On thread-driven I/O platforms, when the CS_ASYNC_NOTIFS property is CS_TRUE, the callback is invoked from an internal Client-Library thread. |
Server message |
When the CS_NETIO connection property is CS_DEFER_IO or CS_SYNC_IO, the callback is invoked from the thread that is processing results or sending commands on the connection when the message arrives.On thread-driven I/O platforms, when the CS_NETIO connection property is CS_ASYNC_IO, the callback is invoked by an internal Client-Library thread. |
Signal |
On platforms that support signals and where Client-Library uses thread-driven I/O, signal callbacks must be installed with ct_callback. The signal callback is invoked by an internal Client-Library thread, and not at interrupt level. |
