Data Sharing

Although the prefetch thread and the computation thread can share data through global variables in the application program, sometimes we may need to share information in other ways. AASFP provides the abstraction of a communication channel between the two threads. This communication channel is provided by the prefetch library and is implemented using a shared buffer between the two threads. Typically the only variables that need to be shared are the common file pointers and the user/file input variables. The following functions support sharing data between the two threads:

• send_fileptr(file_pointer), receive_fileptr(&file_pointer): These functions send and receive file pointers between the threads. The functions provide implicit synchronization and thus eliminate the need to call synchronization functions explicitly. Lines C3 and P1 in Figure 3 are examples.

• send_XXX(), receive_XXX(): These are a set of functions that a thread uses to send/receive data to/from the other thread. They replace the I/O calls of the same name and use almost the same syntax. For example, for the I/O call fscanf(fp, "%d", &value), AASFP provides the send call send_fscanf(fp, "%d", &value), and the receive call receive_fscanf("%d", &value). The send function reads in the value as well as sends it to the communication channel for the other thread to pick up. The variable fp is not needed in the receive call since the receive function receives it from the communication channel. As discussed in Section 3, the prefetch thread performs all the I/O operations on the configuration file; these operations are removed from the computation thread. In Figure 3, lines marked by XX are removed from the computation thread, and lines in the prefetch thread that are not marked by $$ are extracted from the original main function. Instead of fscanf, the prefetch thread performs a send_fscanf, and the computation thread performs a receive_fscanf. These functions also provide implicit synchronization.