Synchronization Variables¶

Synchronization variables have a logical state associated with the value. The state of the variable is either full or empty. Normal reads of a synchronization variable cannot proceed until the variable's state is full. Normal writes of a synchronization variable cannot proceed until the variable's state is empty.

Chapel supports two types of synchronization variables: sync and single. Both types behave similarly, except that a single variable may only be written once. Consequently, when a sync variable is read, its state transitions to empty, whereas when a single variable is read, its state does not change. When either type of synchronization variable is written, its state transitions to full.

If a task attempts to read or write a synchronization variable that is not in the correct state, the task is suspended. When the variable transitions to the correct state, the task is resumed. If there are multiple tasks blocked waiting for the state transition, one is non-deterministically selected to proceed and the others continue to wait if it is a sync variable; all tasks are selected to proceed if it is a single variable.

proc isSyncType(type t) param¶

Returns true if t is a sync type, false otherwise.

proc sync.readFE(): base_type¶

This method blocks until the sync variable is full. The state of the sync variable is set to empty when this method completes. This method implements the default read of a sync variable.

Returns:	The value of the sync variable.

proc sync.readFF()¶

This method blocks until the sync variable is full. The state of the sync variable remains full when this method completes.

Returns:	The value of the sync variable.

proc sync.readXX()¶

This method is non-blocking and the state of the sync variable is unchanged when this method completes.

Returns:	The value of the sync variable.

proc sync.writeEF(val: base_type)¶

Arguments:	val -- New value of the sync variable.

This method blocks until the sync variable is empty. The state of the sync variable is set to full when this method completes. This method implements the default write of a sync variable.

proc sync.writeFF(val: base_type)¶

Arguments:	val -- New value of the sync variable.

This method blocks until the sync variable is full. The state of the sync variable remains full when this method completes.

proc sync.writeXF(val: base_type)¶

Arguments:	val -- New value of the sync variable.

This method is non-blocking and the state of the sync variable is set to full when this method completes.

proc sync.reset()¶

Resets the value of this sync variable to the default value of its type. This method is non-blocking and the state of the sync variable is set to empty when this method completes.

proc sync.isFull¶

Returns:	true if the state of the sync variable is full.

This method is non-blocking and the state of the sync variable is unchanged when this method completes.

proc isSingleType(type t) param¶

Returns true if t is a single type, false otherwise.

proc single.readFF()¶

This method blocks until the single variable is full. The state of the single variable remains full when this method completes. This method implements the default read of a single variable.

Returns:	The value of the single variable.

proc single.readXX()¶

This method is non-blocking and the state of the single variable is unchanged when this method completes.

Returns:	The value of the single variable.

proc single.writeEF(val: base_type)¶

Arguments:	val -- New value of the single variable.

This method blocks until the single variable is empty. The state of the single variable is set to full when this method completes. This method implements the default write of a single variable.

proc single.isFull¶

Returns:	true if the state of the single variable is full.

This method is non-blocking and the state of the single variable is unchanged when this method completes.