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Eliminate a race condition in NSError bridging #3975

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Merged
merged 1 commit into from
Aug 4, 2016
Merged

Eliminate a race condition in NSError bridging #3975

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24 changes: 13 additions & 11 deletions stdlib/public/runtime/ErrorObject.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -79,15 +79,10 @@ - (NSInteger)code {
- (NSDictionary*)userInfo {
auto error = (const SwiftError*)self;
auto userInfo = error->userInfo.load(SWIFT_MEMORY_ORDER_CONSUME);

if (userInfo) {
// Don't need to .retain.autorelease since it's immutable.
return (NSDictionary*)userInfo;
} else {
// -[NSError userInfo] never returns nil on OS X 10.8 or later.
NSDictionary *emptyDict = SWIFT_LAZY_CONSTANT(@{});
return emptyDict;
}
assert(userInfo
&& "Error box used as NSError before initialization");
// Don't need to .retain.autorelease since it's immutable.
return (NSDictionary*)userInfo;
}

- (id)copyWithZone:(NSZone *)zone {
Expand Down Expand Up @@ -319,8 +314,11 @@ typedef SWIFT_CC(swift)
static id _swift_bridgeErrorToNSError_(SwiftError *errorObject) {
auto ns = reinterpret_cast<NSError *>(errorObject);

// If we already have a domain set, then we've already initialized.
if (errorObject->domain.load(SWIFT_MEMORY_ORDER_CONSUME))
// If we already have a domain and userInfo set, then we've already
// initialized.
// FIXME: This might be overly strict; can we look only at the domain?
if (errorObject->domain.load(std::memory_order_acquire) &&
errorObject->userInfo.load(std::memory_order_acquire))
return ns;

// Otherwise, calculate the domain and code (TODO: and user info), and
Expand All @@ -334,6 +332,10 @@ static id _swift_bridgeErrorToNSError_(SwiftError *errorObject) {
NSDictionary *userInfo =
swift_stdlib_getErrorUserInfoNSDictionary(value, type, witness);

// Never produce an empty userInfo dictionary.
if (!userInfo)
userInfo = SWIFT_LAZY_CONSTANT(@{});
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Do we already do this somewhere else? We might want to factor this out into a static helper so there's only one global initializer for all empty dictionaries.

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I eliminated the other place I know about, but I do want to revisit this because on modern platforms we don't need the dispatch_once at all for empty collection literals.


// The error code shouldn't change, so we can store it blindly, even if
// somebody beat us to it. The store can be relaxed, since we'll do a
// store(release) of the domain last thing to publish the initialized
Expand Down
1 change: 0 additions & 1 deletion validation-test/stdlib/ErrorProtocol.swift
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
// RUN: %target-run-simple-swift
// REQUIRES: executable_test
// REQUIRES: rdar27541751
// REQUIRES: objc_interop

import SwiftPrivate
Expand Down