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Normally when a JE transaction is blocked on a lock request, it must wait until the requested lock becomes available before its thread-of-control can proceed. However, it is possible to configure a transaction handle such that it will report a deadlock rather than wait for the block to clear.
You do this on a transaction by transaction basis by specifying DB_TXN_NOWAIT to the DbEnv::txn_begin() method.
For example:
DbTxn *txn = NULL; try { envp->txn_begin(NULL, &txn, DB_TXN_NOWAIT); ... } catch (DbException &de) { // Deadlock detection and exception handling omitted // for brevity ...