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Prevent main thread from destroying flatbuffers globals 

We recently witnessed (using tsan) the main thread exiting without first
joining the network thread, and this caused data races and
heap-use-after-free's

Now the lifetime of these globals will be tied to the network thread
itself (and I guess every thread, but the one that actually uses memory
will be owned by the network thread.)
This commit is contained in:
Andrew Noyes 2020-04-17 23:34:28 +00:00
parent b5d7780293
commit cb6389d42d
2 changed files with 10 additions and 7 deletions
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6
flow/flat_buffers.cpp
View File

@ -31,10 +31,12 @@
namespace detail { namespace detail {
namespace { namespace {
std::vector<int> mWriteToOffsetsMemoy; thread_local std::vector<int> gWriteToOffsetsMemory;
} }
std::vector<int>* writeToOffsetsMemory = &mWriteToOffsetsMemoy; void swapWithThreadLocalGlobal(std::vector<int>& writeToOffsets) {
gWriteToOffsetsMemory.swap(writeToOffsets);
}
VTable generate_vtable(size_t numMembers, const std::vector<unsigned>& sizesAlignments) { VTable generate_vtable(size_t numMembers, const std::vector<unsigned>& sizesAlignments) {
if (numMembers == 0) { if (numMembers == 0) {

11
flow/flat_buffers.h
View File

@ -343,15 +343,16 @@ struct _SizeOf {
static constexpr unsigned int align = fb_align<T>; static constexpr unsigned int align = fb_align<T>;
}; };
extern std::vector<int>* writeToOffsetsMemory; // Re-use this intermediate memory to avoid frequent new/delete
void swapWithThreadLocalGlobal(std::vector<int>& writeToOffsets);
template <class Context> template <class Context>
struct PrecomputeSize : Context { struct PrecomputeSize : Context {
PrecomputeSize(const Context& context) : Context(context) { PrecomputeSize(const Context& context) : Context(context) {
writeToOffsets.swap(*writeToOffsetsMemory); swapWithThreadLocalGlobal(writeToOffsets);
writeToOffsets.clear(); writeToOffsets.clear();
} }
~PrecomputeSize() { writeToOffsets.swap(*writeToOffsetsMemory); } ~PrecomputeSize() { swapWithThreadLocalGlobal(writeToOffsets); }
// |offset| is measured from the end of the buffer. Precondition: len <= // |offset| is measured from the end of the buffer. Precondition: len <=
// offset. // offset.
void write(const void*, int offset, int /*len*/) { current_buffer_size = std::max(current_buffer_size, offset); } void write(const void*, int offset, int /*len*/) { current_buffer_size = std::max(current_buffer_size, offset); }
@ -491,7 +492,7 @@ extern VTable generate_vtable(size_t numMembers, const std::vector<unsigned>& si
template <unsigned... MembersAndAlignments> template <unsigned... MembersAndAlignments>
const VTable* gen_vtable3() { const VTable* gen_vtable3() {
static VTable table = static thread_local VTable table =
generate_vtable(sizeof...(MembersAndAlignments) / 2, std::vector<unsigned>{ MembersAndAlignments... }); generate_vtable(sizeof...(MembersAndAlignments) / 2, std::vector<unsigned>{ MembersAndAlignments... });
return &table; return &table;
} }
@ -619,7 +620,7 @@ VTableSet get_vtableset_impl(const Root& root, const Context& context) {
template <class Root, class Context> template <class Root, class Context>
const VTableSet* get_vtableset(const Root& root, const Context& context) { const VTableSet* get_vtableset(const Root& root, const Context& context) {
static VTableSet result = get_vtableset_impl(root, context); static thread_local VTableSet result = get_vtableset_impl(root, context);
return &result; return &result;
} }