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Diffstat (limited to 'lib/stdlib/doc')
| -rw-r--r-- | lib/stdlib/doc/src/ets.xml | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/lib/stdlib/doc/src/ets.xml b/lib/stdlib/doc/src/ets.xml index e67397c6fd..7594514b29 100644 --- a/lib/stdlib/doc/src/ets.xml +++ b/lib/stdlib/doc/src/ets.xml @@ -188,6 +188,31 @@ is used to keep the table fixated during the entire traversal.</p> </item> </list> + <note> + <p>Even though the access of a single object is always guaranteed to be + <seealso marker="#concurrency">atomic and isolated</seealso>, each traversal + through a table to find the next key is not done with such guarantees. This is often + not a problem, but may cause rare subtle "unexpected" effects if a concurrent + process inserts objects during a traversal. For example, consider one + process doing</p> +<pre> +ets:new(t, [ordered_set, named_table]), +ets:insert(t, {1}), +ets:insert(t, {2}), +ets:insert(t, {3}), +</pre> + <p>A concurrent call to <c>ets:first(t)</c>, done by another + process, may then in rare cases return <c>2</c> even though + <c>2</c> has never existed in the table ordered as the first key. In + the same way, a concurrent call to <c>ets:next(t, 1)</c> may return + <c>3</c> even though <c>3</c> never existed in the table + ordered directly after <c>1</c>.</p> + <p>Effects like this are improbable but possible. The probability will + further be reduced (if not vanish) if table option + <seealso marker="#new_2_write_concurrency"><c>write_concurrency</c></seealso> + is not enabled. This can also only be a potential concern for + <c>ordered_set</c> where the traversal order is defined.</p> + </note> </section> <section> |