[PATCH v1] api: barrier: clarify thread barrier reuse #2262
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Explicitly state that a memory barrier can be reused without initializing it again. Make it clear that no more than N threads may be inside odp_barrier_wait() for a barrier of N threads. Without this requirement, an application could e.g. wait a barrier in thread 1 and thread 2, and, when thread 2 returns from the barrier (at which point thread 1 is supposed to have been unblocked too), tell threads 3 and 4 to wait for the same barrier. If threads 3 and 4 manage to start waiting for the barrier before thread 1 has returned from odp_barrier_wait(), thread 1 may continue to be blocked in the counter based implementation used in multiple ODPs. Clarify that a barrier must be initialized before first use and can be reinitialized if not in use. Make also a remark about the thread-unsafety of the initialization function. Signed-off-by: Janne Peltonen <[email protected]>
odpbuild
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MatiasElo
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Sep 22, 2025
| /** | ||
| * Initialize barrier with thread count. | ||
| * | ||
| * This function must not be called by multiple threads simultaenously for |
| * If a barrier is used by more threads than the thread count the barrier was | ||
| * initialized with, the number of threads that have called odp_barrier_wait() | ||
| * but not yet returned from it must never exceed the thread count the barrier | ||
| * was initiazed with. |
| /** | ||
| * Synchronize thread execution on barrier. | ||
| * Wait for all threads to arrive at the barrier until they are let loose again. | ||
| * Wait for a number of threads to arrive at the barrier until they are |
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Could add also a newline to separate the one-line description.
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| * A barrier can be reused without reinitializing it again. It is ok to call | ||
| * odp_barrier_wait() for the same barrier again immediately after returning | ||
| * from the previous odp_barrier_wait() even if other threads that were waiting | ||
| * for the barrier have not yet returned from odp_barrier_wait(). |
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Do we have a validation test already for this? If not, one should be added.
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We have multiple tests that rely on this, so in a way we have, but maybe it would be good add an explicit test.
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Yep, explicit test seems worth adding.
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Explicitly state that a memory barrier can be reused without initializing it again.
Make it clear that no more than N threads may be inside odp_barrier_wait() for a barrier of N threads. Without this requirement, an application could e.g. wait a barrier in thread 1 and thread 2, and, when thread 2 returns from the barrier (at which point thread 1 is supposed to have been unblocked too), tell threads 3 and 4 to wait for the same barrier. If threads 3 and 4 manage to start waiting for the barrier before thread 1 has returned from odp_barrier_wait(), thread 1 may continue to be blocked in the counter based implementation used in multiple ODPs.
Clarify that a barrier must be initialized before first use and can be reinitialized if not in use. Make also a remark about the thread-unsafety of the initialization function.