diff options
Diffstat (limited to 'lib/stdlib')
| -rw-r--r-- | lib/stdlib/doc/src/ets.xml | 36 | ||||
| -rw-r--r-- | lib/stdlib/test/ets_SUITE.erl | 20 |
2 files changed, 48 insertions, 8 deletions
diff --git a/lib/stdlib/doc/src/ets.xml b/lib/stdlib/doc/src/ets.xml index 0d1e5c6e3a..342be80f98 100644 --- a/lib/stdlib/doc/src/ets.xml +++ b/lib/stdlib/doc/src/ets.xml @@ -1495,17 +1495,37 @@ is_integer(X), is_integer(Y), X + Y < 4711]]></code> <fsummary>Match and replace objects atomically in an ETS table</fsummary> <desc> <p>Matches the objects in the table <c><anno>Tab</anno></c> using a - <seealso marker="#match_spec">match specification</seealso>. If - an object is matched, the existing object is replaced with - the match specification result, which <em>must</em> retain - the original key or the operation will fail with <c>badarg</c>.</p> + <seealso marker="#match_spec">match specification</seealso>. For each + matched object, the existing object is replaced with + the match specification result.</p> + <p>The match-and-replace operation for each individual object is guaranteed to be + <seealso marker="#concurrency">atomic and isolated</seealso>. The + <c>select_replace</c> table iteration as a whole, like all other select functions, + does not give such guarantees.</p> + <p>The match specifiction must be guaranteed to <em>retain the key</em> + of any matched object. If not, <c>select_replace</c> will fail with <c>badarg</c> + without updating any objects.</p> <p>For the moment, due to performance and semantic constraints, tables of type <c>bag</c> are not yet supported.</p> <p>The function returns the total number of replaced objects.</p> - <note> - <p>The match/replacement operation atomicity scope is limited - to each individual object.</p> - </note> + <p><em>Example</em></p> + <p>For all 2-tuples with a list in second position, add atom <c>'marker'</c> first in the list:</p> + <pre> +1> <input>T = ets:new(x,[]), ets:insert(T, {key, [1, 2, 3]}).</input> +true +2> <input>MS = ets:fun2ms(fun({K, L}) when is_list(L) -> {K, [marker | L]} end).</input> +[{{'$1','$2'},[{is_list,'$2'}],[{{'$1',[marker|'$2']}}]}] +3> <input>ets:select_replace(T, MS).</input> +1 +4> <input>ets:tab2list(T).</input> +[{key,[marker,1,2,3]}] + </pre> + <p>A generic single object compare-and-swap operation:</p> + <pre> +[Old] = ets:lookup(T, Key), +New = update_object(Old), +Success = (1 =:= ets:select_replace(T, [{Old, [], [{const, New}]}])), + </pre> </desc> </func> diff --git a/lib/stdlib/test/ets_SUITE.erl b/lib/stdlib/test/ets_SUITE.erl index 4c2f6cfe9e..05451a83fb 100644 --- a/lib/stdlib/test/ets_SUITE.erl +++ b/lib/stdlib/test/ets_SUITE.erl @@ -1349,6 +1349,26 @@ t_select_replace(Config) when is_list(Config) -> NeqPairs(X,Y)) || X <- Terms, Y <- Terms], + %% Wrap entire tuple with 'const' + [[begin + Old = {Key, 1, 2}, + ets:insert(T2, Old), + 1 = ets:select_replace(T2, [{Old, [], [{const, New}]}]), + [New] = ets:lookup(T2, Key), + ets:delete(T2, Key) + end || New <- [{Key, 1, 2}, {Key, 3, 4}, {Key, 1}, {Key, 1, 2, 3}, {Key}] + ] + || Key <- [{1, tuple}, {nested, {tuple, {a,b}}} | Terms]], + + %% 'const' wrap does not work with maps or variables in keys + [[begin + Old = {Key, 1, 2}, + {'EXIT',{badarg,_}} = (catch ets:select_replace(T2, [{Old, [], [{const, New}]}])) + end || New <- [{Key, 1, 2}, {Key, 3, 4}, {Key, 1}, {Key, 1, 2, 3}, {Key}] + ] + || Key <- [#{a => 1}, {nested, #{a => 1}}, '$1']], + + ets:delete(T2), verify_etsmem(EtsMem). |