ODBC call SQLCancel is blocking if called for synchronous statements
Details
| Detail name | Value |
|---|---|
| Changelog Number | 6946 |
| Type | Bug |
| Status | Resolved |
| Affected Versions | EXASOL 6.0.0 |
| Fix Versions | Exasol 6.0.13 |
| Resolution Date | 2018-11-13 |
Background
In ODBC, statements can be executed in synchronous (API call blocks until the server is done processing) or asynchronous mode (API call returns immediately, application polls for results). ODBC 2.0 application can call SQLCancel on synchronous statement handles to close the cursor (see docs.microsoft.com).
Problem
Exasol's implementation of SQLCancel does not return when called for a statement being processed in synchronous mode.
Fix
If SQLCancel is called while a statement is running (in asynchronous mode or from another thread), the statement will be canceled and the return code for this can be checked in the thread executing the statement.
In case no statement is running: If the application tells the driver that it needs ODBC 2.0 behavior, we map the SQLCancel call to a call of SQLFreeStmt (SQL_CLOSE) what closes the cursor. For applications that do not need ODBC 2.0 behavior, SQLCancel returns without doing anything.
