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// workqueue.cc -- the workqueue for gold
#include "gold.h"
#include "workqueue.h"
namespace gold
{
// Task_token methods.
Task_token::Task_token()
: is_blocker_(false), readers_(0), writer_(NULL)
{
}
Task_token::~Task_token()
{
assert(this->readers_ == 0 && this->writer_ == NULL);
}
bool
Task_token::is_readable() const
{
assert(!this->is_blocker_);
return this->writer_ == NULL;
}
void
Task_token::add_reader()
{
assert(!this->is_blocker_);
assert(this->is_readable());
++this->readers_;
}
void
Task_token::remove_reader()
{
assert(!this->is_blocker_);
assert(this->readers_ > 0);
--this->readers_;
}
bool
Task_token::is_writable() const
{
assert(!this->is_blocker_);
return this->writer_ == NULL && this->readers_ == 0;
}
void
Task_token::add_writer(const Task* t)
{
assert(!this->is_blocker_);
assert(this->is_writable());
this->writer_ = t;
}
void
Task_token::remove_writer(const Task* t)
{
assert(!this->is_blocker_);
assert(this->writer_ == t);
this->writer_ = NULL;
}
bool
Task_token::has_write_lock(const Task* t)
{
assert(!this->is_blocker_);
return this->writer_ == t;
}
// For blockers, we just use the readers_ field.
void
Task_token::add_blocker()
{
if (this->readers_ == 0 && this->writer_ == NULL)
this->is_blocker_ = true;
else
assert(this->is_blocker_);
++this->readers_;
}
bool
Task_token::remove_blocker()
{
assert(this->is_blocker_ && this->readers_ > 0);
--this->readers_;
return this->readers_ == 0;
}
bool
Task_token::is_blocked() const
{
assert(this->is_blocker_ || (this->readers_ == 0 && this->writer_ == NULL));
return this->readers_ > 0;
}
// The Task_block_token class.
Task_block_token::Task_block_token(Task_token& token, Workqueue* workqueue)
: token_(token), workqueue_(workqueue)
{
// We must increment the block count when the task is created and
// put on the queue. This object is created when the task is run,
// so we don't increment the block count here.
assert(this->token_.is_blocked());
}
Task_block_token::~Task_block_token()
{
if (this->token_.remove_blocker())
{
// Tell the workqueue that a blocker was cleared. This is
// always called in the main thread, so no locking is required.
this->workqueue_->cleared_blocker();
}
}
// The Workqueue_runner abstract class.
class Workqueue_runner
{
public:
Workqueue_runner(Workqueue* workqueue)
: workqueue_(workqueue)
{ }
virtual ~Workqueue_runner()
{ }
// Run a task. This is always called in the main thread.
virtual void run(Task*, Task_locker*) = 0;
protected:
// This is called by an implementation when a task is completed.
void completed(Task* t, Task_locker* tl)
{ this->workqueue_->completed(t, tl); }
Workqueue* get_workqueue() const
{ return this->workqueue_; }
private:
Workqueue* workqueue_;
};
// The simple single-threaded implementation of Workqueue_runner.
class Workqueue_runner_single : public Workqueue_runner
{
public:
Workqueue_runner_single(Workqueue* workqueue)
: Workqueue_runner(workqueue)
{ }
~Workqueue_runner_single()
{ }
void run(Task*, Task_locker*);
};
void
Workqueue_runner_single::run(Task* t, Task_locker* tl)
{
t->run(this->get_workqueue());
this->completed(t, tl);
}
// Workqueue methods.
Workqueue::Workqueue(const General_options&)
: tasks_lock_(),
tasks_(),
completed_lock_(),
completed_(),
running_(0),
completed_condvar_(this->completed_lock_),
cleared_blockers_(0)
{
// At some point we will select the specific implementation of
// Workqueue_runner to use based on the command line options.
this->runner_ = new Workqueue_runner_single(this);
}
Workqueue::~Workqueue()
{
assert(this->tasks_.empty());
assert(this->completed_.empty());
assert(this->running_ == 0);
}
void
Workqueue::queue(Task* t)
{
Hold_lock hl(this->tasks_lock_);
this->tasks_.push_back(t);
}
// Clear the list of completed tasks. Return whether we cleared
// anything. The completed_lock_ must be held when this is called.
bool
Workqueue::clear_completed()
{
if (this->completed_.empty())
return false;
do
{
delete this->completed_.front();
this->completed_.pop_front();
}
while (!this->completed_.empty());
return true;
}
// Find a runnable task in TASKS, which is non-empty. Return NULL if
// none could be found. The tasks_lock_ must be held when this is
// called. Sets ALL_BLOCKED if all non-runnable tasks are waiting on
// a blocker.
Task*
Workqueue::find_runnable(Task_list& tasks, bool* all_blocked)
{
Task* tlast = tasks.back();
*all_blocked = true;
while (true)
{
Task* t = tasks.front();
tasks.pop_front();
Task::Is_runnable_type is_runnable = t->is_runnable(this);
if (is_runnable == Task::IS_RUNNABLE)
return t;
if (is_runnable != Task::IS_BLOCKED)
*all_blocked = false;
tasks.push_back(t);
if (t == tlast)
{
// We couldn't find any runnable task. If there are any
// completed tasks, free their locks and try again.
{
Hold_lock hl2(this->completed_lock_);
if (!this->clear_completed())
{
// There had better be some tasks running, or we will
// never find a runnable task.
assert(this->running_ > 0);
// We couldn't find any runnable tasks, and we
// couldn't release any locks.
return NULL;
}
}
// We're going around again, so recompute ALL_BLOCKED.
*all_blocked = true;
}
}
}
// Process all the tasks on the workqueue. This is the main loop in
// the linker. Note that as we process tasks, new tasks will be
// added.
void
Workqueue::process()
{
while (true)
{
Task* t;
bool empty;
bool all_blocked;
{
Hold_lock hl(this->tasks_lock_);
if (this->tasks_.empty())
{
t = NULL;
empty = true;
all_blocked = false;
}
else
{
t = this->find_runnable(this->tasks_, &all_blocked);
empty = false;
}
}
// If T != NULL, it is a task we can run.
// If T == NULL && empty, then there are no tasks waiting to
// be run at this level.
// If T == NULL && !empty, then there tasks waiting to be
// run at this level, but they are waiting for something to
// unlock.
if (t != NULL)
this->run(t);
else if (!empty)
{
{
Hold_lock hl(this->completed_lock_);
// There must be something for us to wait for, or we won't
// be able to make progress.
assert(this->running_ > 0 || !this->completed_.empty());
if (all_blocked)
{
this->cleared_blockers_ = 0;
this->clear_completed();
while (this->cleared_blockers_ == 0)
{
assert(this->running_ > 0);
this->completed_condvar_.wait();
this->clear_completed();
}
}
else
{
if (this->running_ > 0)
{
// Wait for a task to finish.
this->completed_condvar_.wait();
}
this->clear_completed();
}
}
}
else
{
{
Hold_lock hl(this->completed_lock_);
// If there are no running tasks, then we are done.
if (this->running_ == 0)
{
this->clear_completed();
return;
}
// Wait for a task to finish. Then we have to loop around
// again in case it added any new tasks before finishing.
this->completed_condvar_.wait();
this->clear_completed();
}
}
}
}
// Run a task. This is always called in the main thread.
void
Workqueue::run(Task* t)
{
++this->running_;
this->runner_->run(t, t->locks(this));
}
// This is called when a task is completed to put the locks on the
// list to be released. We use a list because we only want the locks
// to be released in the main thread.
void
Workqueue::completed(Task* t, Task_locker* tl)
{
{
Hold_lock hl(this->completed_lock_);
assert(this->running_ > 0);
--this->running_;
this->completed_.push_back(tl);
this->completed_condvar_.signal();
}
delete t;
}
// This is called when the last task for a blocker has completed.
// This is always called in the main thread.
void
Workqueue::cleared_blocker()
{
++this->cleared_blockers_;
}
} // End namespace gold.
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