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branches: re-link default_minfreespace pointer on copy/move; atomically publish branch mode changes

Browse source 
Branches using the default minfreespace held a reference to their
owning Impl's _default_minfreespace. After a copy or move the
pointer still referenced the source Impl, which could become
invalid or diverge after further configuration changes. Switch to
a pointer and re-link it to the destination Impl on copy/move.

While here, convert set_branch_mode to do an atomic_store of a
newly constructed Impl rather than mutating the shared pointer
target in place. Readers holding an atomic_load snapshot are no
longer affected by a concurrent mode change.
This commit is contained in:
Antonio S. Musumeci 2026-04-18 00:45:32 -04:00
parent deba02e3d3
commit da3cb9ae56
2 changed files with 46 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

51
src/branches.cpp
View file

@ -34,7 +34,7 @@
#include <fnmatch.h>
Branches::Impl::Impl(const u64 &default_minfreespace_)
Branches::Impl::Impl(const u64 *default_minfreespace_)
: _default_minfreespace(default_minfreespace_)
{
}
@ -48,6 +48,16 @@ Branches::Impl::operator=(Branches::Impl &rval_)
*this_base = *rval_base;
// Branches using the default minfreespace hold a pointer to their
// owning Impl's _default_minfreespace. After copy/move those
// pointers still reference the source Impl, so re-link them to this
// Impl's _default_minfreespace.
for(auto &branch : *this)
{
if(std::holds_alternative<const u64*>(branch._minfreespace))
branch._minfreespace = _default_minfreespace;
}
return *this;
}
@ -60,6 +70,16 @@ Branches::Impl::operator=(Branches::Impl &&rval_)
*this_base = std::move(*rval_base);
// Branches using the default minfreespace hold a pointer to their
// owning Impl's _default_minfreespace. After copy/move those
// pointers still reference the source Impl, so re-link them to this
// Impl's _default_minfreespace.
for(auto &branch : *this)
{
if(std::holds_alternative<const u64*>(branch._minfreespace))
branch._minfreespace = _default_minfreespace;
}
return *this;
}
@ -67,7 +87,7 @@ const
u64&
Branches::Impl::minfreespace(void) const
{
return _default_minfreespace;
return *_default_minfreespace;
}
namespace l
@ -148,7 +168,7 @@ namespace l
case 2:
*glob_ = v[0];
options = v[1];
v = str::split(options,',');
v = str::split(options,',');
switch(v.size())
{
case 2:
@ -229,7 +249,7 @@ namespace l
{
int rv;
StrVec paths;
Branches::Impl tmp_branches(branches_->minfreespace());
Branches::Impl tmp_branches(&branches_->minfreespace());
paths = str::split(str_,':');
for(auto &path : paths)
@ -251,7 +271,7 @@ namespace l
{
int rv;
std::vector<std::string> paths;
Branches::Impl tmp_branches(branches_->minfreespace());
Branches::Impl tmp_branches(&branches_->minfreespace());
paths = str::split(str_,':');
for(auto &path : paths)
@ -275,7 +295,7 @@ namespace l
{
int rv;
StrVec paths;
Branches::Impl tmp_branches(branches_->minfreespace());
Branches::Impl tmp_branches(&branches_->minfreespace());
paths = str::split(str_,':');
for(auto &path : paths)
@ -419,7 +439,7 @@ Branches::from_string(const std::string_view str_)
impl = std::atomic_load(&_impl);
new_impl = std::make_shared<Branches::Impl>(impl->minfreespace());
new_impl = std::make_shared<Branches::Impl>(&minfreespace);
*new_impl = *impl;
rv = new_impl->from_string(str_);
@ -440,7 +460,16 @@ Branches::to_string(void) const
void
Branches::find_and_set_mode_ro()
{
for(auto &branch : *_impl)
Branches::Ptr impl;
Branches::Ptr new_impl;
impl = std::atomic_load(&_impl);
new_impl = std::make_shared<Branches::Impl>(&minfreespace);
*new_impl = *impl;
bool changed = false;
for(auto &branch : *new_impl)
{
if(branch.mode != Branch::Mode::RW)
continue;
@ -452,7 +481,13 @@ Branches::find_and_set_mode_ro()
branch.path.string());
branch.mode = Branch::Mode::RO;
changed = true;
}
if(not changed)
return;
std::atomic_store(&_impl,new_impl);
}
SrcMounts::SrcMounts(Branches &b_)

6
src/branches.hpp
View file

@ -39,13 +39,13 @@ public:
public std::vector<Branch>
{
private:
const u64 &_default_minfreespace;
const u64 *_default_minfreespace;
public:
using Ptr = std::shared_ptr<Impl>;
public:
Impl(const u64 &default_minfreespace);
Impl(const u64 *default_minfreespace);
public:
int from_string(const std::string_view str) final;
@ -73,7 +73,7 @@ private:
public:
Branches()
: _impl(std::make_shared<Impl>(minfreespace))
: _impl(std::make_shared<Impl>(&minfreespace))
{
}