7.5 Committing a Speculation

You commit speculations by using the commit function. When a speculative buffer is committed, its data is copied into the principal buffer. If there is more data in the specified speculative buffer than there is available space in the principal buffer, no data is copied and the drop count for the buffer is incremented. If the buffer has been speculatively traced on more than one CPU, the speculative data on the committing CPU is copied immediately, while speculative data on other CPUs is copied some time after the commit. Thus, some time might elapse between a commit that begins on one CPU, while the data is being copied from speculative buffers to principal buffers on all CPUs. This length of time is guaranteed to be no longer than the time dictated by the cleaning rate. See Section 7.8, “Speculation Options and Tuning”.

A committing speculative buffer is not made available to subsequent speculation calls until each per-CPU speculative buffer has been completely copied into its corresponding per-CPU principal buffer. Similarly, subsequent calls to speculate to the committing buffer are silently discarded, and subsequent calls to commit or discard silently fail. Finally, a clause containing a commit cannot contain a data recording action. However, a clause can contain multiple commit calls to commit disjoint buffers.