From 130c166697cc7df082197a10936dd9554c3e4083 Mon Sep 17 00:00:00 2001 From: Thomas Van Lenten Date: Wed, 29 Mar 2017 10:46:04 -0400 Subject: Remove the use of dispatch_once that is heap backed. Apple recently updated the docs on dispatch_once to point out that the storage for the dispatch_once_t must be static or global, but not something that was ever used before as the implementation doesn't use a memory barrier. So we drop the use and create the semaphore when needed and use an atomic swap deal with any threading races. --- objectivec/GPBMessage.m | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'objectivec/GPBMessage.m') diff --git a/objectivec/GPBMessage.m b/objectivec/GPBMessage.m index 58a10fdb..78935b19 100644 --- a/objectivec/GPBMessage.m +++ b/objectivec/GPBMessage.m @@ -738,6 +738,25 @@ void GPBClearMessageAutocreator(GPBMessage *self) { self->autocreatorExtension_ = nil; } +// Call this before using the readOnlySemaphore_. This ensures it is created only once. +void GPBPrepareReadOnlySemaphore(GPBMessage *self) { +#pragma clang diagnostic push +#pragma clang diagnostic ignored "-Wdirect-ivar-access" +#pragma clang diagnostic ignored "-Wdeprecated-declarations" + + // Create the semaphore on demand (rather than init) as developers might not cause them + // to be needed, and the heap usage can add up. The atomic swap is used to avoid needing + // another lock around creating it. + if (self->readOnlySemaphore_ == nil) { + dispatch_semaphore_t worker = dispatch_semaphore_create(1); + if (!OSAtomicCompareAndSwapPtrBarrier(NULL, worker, (void * volatile *)&(self->readOnlySemaphore_))) { + dispatch_release(worker); + } + } + +#pragma clang diagnostic pop +} + static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) { if (!self->unknownFields_) { self->unknownFields_ = [[GPBUnknownFieldSet alloc] init]; -- cgit v1.2.3