The barrier library

The barrier.c and barrier.h files define an user level synchronisation service between several tasks sharing the same address space in a parallel multi-tasks application.

There is actually two types of barriers:

A) Simple Barrier

The giet_barrier_t is a simple sense-reversing barrier. It can be safely used several times (in a loop for example), but it does not scale, and should not be used when the number of expected tasks is larger than few tens.

The available functions are:

• barrier_init( giet_barrier_t * barrier, unsigned int ntasks )
• barrier_wait( giet_barrier_t * barrier )

The barrier argument is a pointer on a giet_barrier_t object. The ntasks argument is the number of expected tasks.

Neither the barrier_init(), nor the barrier_wait() function contains a system call.

B) Distributed Barrier

The giet_sbt_barrier_t can be used in multi-clusters architectures, and is implemented as a - physically distributed - Synchronisation-Quad-Tree (SQT). The SQT topology is completely defined by the (x_size / y_size) parameters, with the following constraints:

• The involved clusters form a mesh(x_size * y_size).
• The lower left involved cluster is cluster(0,0).
• All involved clusters must contain a heap_x_y vseg declared in the mapping.
• The number of involved tasks in a given cluster is the same for all involved clusters.

The available functions are:

• sqt_barrier_init( giet_sbt_barrier_t * barrier, unsigned int x_size, unsigned int y_size, unsigned int ntasks )
• sqt_barrier_wait( giet_sbt_barrier_t * barrier )

The barrier argument is a pointer on a giet_barrier_t object. The x_size argument is the number of clusters in a row. The y_size argument is the number of clusters in a column. The ntasks argument is the number of expected tasks in a single cluster.

C) Barrier Initialization

For both types of barriers, the barrier initialization must be done by one single task.