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Refactoring of the TaskLocal::Item #77241

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Merged
merged 1 commit into from
Oct 28, 2024
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Refactoring of the TaskLocal::Item #77241

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47 changes: 12 additions & 35 deletions stdlib/public/Concurrency/Task.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1027,48 +1027,25 @@ swift_task_create_commonImpl(size_t rawTaskCreateFlags,
if ((group && group->isCancelled()) || swift_task_isCancelled(parent))
swift_task_cancel(task);

// Initialize task locals storage
bool taskLocalStorageInitialized = false;

// Inside a task group, we may have to perform some defensive copying,
// check if doing so is necessary, and initialize storage using partial
// defensive copies if necessary.
if (group) {
assert(parent && "a task created in a group must be a child task");
// We are a child task in a task group; and it may happen that we are calling
// addTask specifically in such shape:
//
// $local.withValue(theValue) { addTask {} }
//
// If this is the case, we MUST copy `theValue` (and any other such directly
// wrapping the addTask value bindings), because those values will be popped
// when withValue returns - breaking our structured concurrency guarantees
// that we rely on for the "link directly to parent's task local Item".
//
// Values set outside the task group are not subject to this problem, as
// their structural lifetime guarantee is upheld by the group scope
// out-living any addTask created tasks.
auto ParentLocal = parent->_private().Local;
// If we were going to copy ALL values anyway, we don't need to
// perform this defensive partial copying. In practice, we currently
// do not have child tasks which force copying, but we could.
assert(!taskCreateFlags.copyTaskLocals() &&
"Currently we don't have child tasks which force copying task "
"locals; unexpected attempt to combine the two!");

if (auto taskLocalHeadLinkType = ParentLocal.peekHeadLinkType()) {
if (taskLocalHeadLinkType ==
swift::TaskLocal::NextLinkType::IsNextCreatedInTaskGroupBody) {
ParentLocal.copyToOnlyOnlyFromCurrentGroup(task);
taskLocalStorageInitialized = true;
}
}
}

if (!taskLocalStorageInitialized) {
// just initialize the storage normally
task->_private().Local.initializeLinkParent(task, parent);
}
// Initialize task locals with a link to the parent task.
//
// Inside a task group, we may have to perform some defensive copying,
// and initialize storage using partial defensive copies if necessary.
//
// If we were going to copy ALL values anyway, we don't need to
// perform this defensive partial copying. In practice, we currently
// do not have child tasks which force copying, but we could.
assert(!taskCreateFlags.copyTaskLocals() &&
"Currently we don't have child tasks which force copying task "
"locals; unexpected attempt to combine the two!");
task->_private().Local.initializeLinkParent(task, parent);
}

// Configure the initial context.
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