blob: 6075149fa7c1253623b662c310b40af3b1a47cc9 [file] [log] [blame]
// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "mojo/system/core_impl.h"
#include <vector>
#include "base/logging.h"
#include "mojo/system/dispatcher.h"
#include "mojo/system/limits.h"
#include "mojo/system/memory.h"
#include "mojo/system/message_pipe.h"
#include "mojo/system/message_pipe_dispatcher.h"
#include "mojo/system/waiter.h"
namespace mojo {
namespace system {
// Implementation notes
//
// Mojo primitives are implemented by the singleton |CoreImpl| object. Most
// calls are for a "primary" handle (the first argument).
// |CoreImpl::GetDispatcher()| is used to look up a |Dispatcher| object for a
// given handle. That object implements most primitives for that object. The
// wait primitives are not attached to objects and are implemented by |CoreImpl|
// itself.
//
// Some objects have multiple handles associated to them, e.g., message pipes
// (which have two). In such a case, there is still a |Dispatcher| (e.g.,
// |MessagePipeDispatcher|) for each handle, with each handle having a strong
// reference to the common "secondary" object (e.g., |MessagePipe|). This
// secondary object does NOT have any references to the |Dispatcher|s (even if
// it did, it wouldn't be able to do anything with them due to lock order
// requirements -- see below).
//
// Waiting is implemented by having the thread that wants to wait call the
// |Dispatcher|s for the handles that it wants to wait on with a |Waiter|
// object; this |Waiter| object may be created on the stack of that thread or be
// kept in thread local storage for that thread (TODO(vtl): future improvement).
// The |Dispatcher| then adds the |Waiter| to a |WaiterList| that's either owned
// by that |Dispatcher| (see |SimpleDispatcher|) or by a secondary object (e.g.,
// |MessagePipe|). To signal/wake a |Waiter|, the object in question -- either a
// |SimpleDispatcher| or a secondary object -- talks to its |WaiterList|.
// Thread-safety notes
//
// Mojo primitives calls are thread-safe. We achieve this with relatively
// fine-grained locking. There is a global handle table lock. This lock should
// be held as briefly as possible (TODO(vtl): a future improvement would be to
// switch it to a reader-writer lock). Each |Dispatcher| object then has a lock
// (which subclasses can use to protect their data).
//
// The lock ordering is as follows:
// 1. global handle table lock
// 2. |Dispatcher| locks
// 3. secondary object locks
// ...
// INF. |Waiter| locks
//
// Notes:
// - While holding a |Dispatcher| lock, you may not unconditionally attempt
// to take another |Dispatcher| lock. (This has consequences on the
// concurrency semantics of |MojoWriteMessage()| when passing handles.)
// Doing so would lead to deadlock.
// - Locks at the "INF" level may not have any locks taken while they are
// held.
CoreImpl::HandleTableEntry::HandleTableEntry()
: busy(false) {
}
CoreImpl::HandleTableEntry::HandleTableEntry(
const scoped_refptr<Dispatcher>& dispatcher)
: dispatcher(dispatcher),
busy(false) {
}
CoreImpl::HandleTableEntry::~HandleTableEntry() {
DCHECK(!busy);
}
// static
CoreImpl* CoreImpl::singleton_ = NULL;
// static
void CoreImpl::Init() {
CHECK(!singleton_);
singleton_ = new CoreImpl();
}
MojoResult CoreImpl::Close(MojoHandle handle) {
if (handle == MOJO_HANDLE_INVALID)
return MOJO_RESULT_INVALID_ARGUMENT;
scoped_refptr<Dispatcher> dispatcher;
{
base::AutoLock locker(handle_table_lock_);
HandleTableMap::iterator it = handle_table_.find(handle);
if (it == handle_table_.end())
return MOJO_RESULT_INVALID_ARGUMENT;
if (it->second.busy)
return MOJO_RESULT_BUSY;
dispatcher = it->second.dispatcher;
handle_table_.erase(it);
}
// The dispatcher doesn't have a say in being closed, but gets notified of it.
// Note: This is done outside of |handle_table_lock_|. As a result, there's a
// race condition that the dispatcher must handle; see the comment in
// |Dispatcher| in dispatcher.h.
return dispatcher->Close();
}
MojoResult CoreImpl::Wait(MojoHandle handle,
MojoWaitFlags flags,
MojoDeadline deadline) {
return WaitManyInternal(&handle, &flags, 1, deadline);
}
MojoResult CoreImpl::WaitMany(const MojoHandle* handles,
const MojoWaitFlags* flags,
uint32_t num_handles,
MojoDeadline deadline) {
if (!VerifyUserPointer<MojoHandle>(handles, num_handles))
return MOJO_RESULT_INVALID_ARGUMENT;
if (!VerifyUserPointer<MojoWaitFlags>(flags, num_handles))
return MOJO_RESULT_INVALID_ARGUMENT;
if (num_handles < 1)
return MOJO_RESULT_INVALID_ARGUMENT;
if (num_handles > kMaxWaitManyNumHandles)
return MOJO_RESULT_RESOURCE_EXHAUSTED;
return WaitManyInternal(handles, flags, num_handles, deadline);
}
MojoResult CoreImpl::CreateMessagePipe(MojoHandle* handle_0,
MojoHandle* handle_1) {
if (!VerifyUserPointer<MojoHandle>(handle_0, 1))
return MOJO_RESULT_INVALID_ARGUMENT;
if (!VerifyUserPointer<MojoHandle>(handle_1, 1))
return MOJO_RESULT_INVALID_ARGUMENT;
scoped_refptr<MessagePipeDispatcher> dispatcher_0(
new MessagePipeDispatcher());
scoped_refptr<MessagePipeDispatcher> dispatcher_1(
new MessagePipeDispatcher());
MojoHandle h0, h1;
{
base::AutoLock locker(handle_table_lock_);
h0 = AddDispatcherNoLock(dispatcher_0);
if (h0 == MOJO_HANDLE_INVALID)
return MOJO_RESULT_RESOURCE_EXHAUSTED;
h1 = AddDispatcherNoLock(dispatcher_1);
if (h1 == MOJO_HANDLE_INVALID) {
handle_table_.erase(h0);
return MOJO_RESULT_RESOURCE_EXHAUSTED;
}
}
scoped_refptr<MessagePipe> message_pipe(new MessagePipe());
dispatcher_0->Init(message_pipe, 0);
dispatcher_1->Init(message_pipe, 1);
*handle_0 = h0;
*handle_1 = h1;
return MOJO_RESULT_OK;
}
MojoResult CoreImpl::WriteMessage(
MojoHandle handle,
const void* bytes, uint32_t num_bytes,
const MojoHandle* handles, uint32_t num_handles,
MojoWriteMessageFlags flags) {
scoped_refptr<Dispatcher> dispatcher(GetDispatcher(handle));
if (!dispatcher.get())
return MOJO_RESULT_INVALID_ARGUMENT;
// Easy case: not sending any handles.
if (num_handles == 0)
return dispatcher->WriteMessage(bytes, num_bytes, NULL, flags);
// We have to handle |handles| here, since we have to mark them busy in the
// global handle table. We can't delegate this to the dispatcher, since the
// handle table lock must be acquired before the dispatcher lock.
//
// (This leads to an oddity: |handles|/|num_handles| are always verified for
// validity, even for dispatchers that don't support |WriteMessage()| and will
// simply return failure unconditionally. It also breaks the usual
// left-to-right verification order of arguments.)
if (!VerifyUserPointer<MojoHandle>(handles, num_handles))
return MOJO_RESULT_INVALID_ARGUMENT;
if (num_handles > kMaxMessageNumHandles)
return MOJO_RESULT_RESOURCE_EXHAUSTED;
// We'll need to hold on to the dispatchers so that we can pass them on to
// |WriteMessage()| and also so that we can unlock their locks afterwards
// without accessing the handle table. These can be dumb pointers, since their
// entries in the handle table won't get removed (since they'll be marked as
// busy).
std::vector<Dispatcher*> dispatchers(num_handles);
// When we pass handles, we have to try to take all their dispatchers' locks
// and mark the handles as busy. If the call succeeds, we then remove the
// handles from the handle table.
{
base::AutoLock locker(handle_table_lock_);
std::vector<HandleTableEntry*> entries(num_handles);
// First verify all the handles and get their dispatchers.
uint32_t i;
MojoResult error_result = MOJO_RESULT_INTERNAL;
for (i = 0; i < num_handles; i++) {
// Sending your own handle is not allowed (and, for consistency, returns
// "busy").
if (handles[i] == handle) {
error_result = MOJO_RESULT_BUSY;
break;
}
HandleTableMap::iterator it = handle_table_.find(handles[i]);
if (it == handle_table_.end()) {
error_result = MOJO_RESULT_INVALID_ARGUMENT;
break;
}
entries[i] = &it->second;
if (entries[i]->busy) {
error_result = MOJO_RESULT_BUSY;
break;
}
// Note: By marking the handle as busy here, we're also preventing the
// same handle from being sent multiple times in the same message.
entries[i]->busy = true;
// Try to take the lock.
if (!entries[i]->dispatcher->lock().Try()) {
// Unset the busy flag (since it won't be unset below).
entries[i]->busy = false;
error_result = MOJO_RESULT_BUSY;
break;
}
// We shouldn't race with things that close dispatchers, since closing can
// only take place either under |handle_table_lock_| or when the handle is
// marked as busy.
DCHECK(!entries[i]->dispatcher->is_closed_no_lock());
// Hang on to the pointer to the dispatcher (which we'll need to release
// the lock without going through the handle table).
dispatchers[i] = entries[i]->dispatcher;
}
if (i < num_handles) {
DCHECK_NE(error_result, MOJO_RESULT_INTERNAL);
// Unset the busy flags and release the locks.
for (uint32_t j = 0; j < i; j++) {
DCHECK(entries[j]->busy);
entries[j]->busy = false;
entries[j]->dispatcher->lock().Release();
}
return error_result;
}
}
MojoResult rv = dispatcher->WriteMessage(bytes, num_bytes,
&dispatchers,
flags);
// We need to release the dispatcher locks before we take the handle table
// lock.
for (uint32_t i = 0; i < num_handles; i++) {
dispatchers[i]->lock().AssertAcquired();
dispatchers[i]->lock().Release();
}
if (rv == MOJO_RESULT_OK) {
base::AutoLock locker(handle_table_lock_);
// Succeeded, so the handles should be removed from the handle table. (The
// transferring to new dispatchers/closing must have already been done.)
for (uint32_t i = 0; i < num_handles; i++) {
HandleTableMap::iterator it = handle_table_.find(handles[i]);
DCHECK(it != handle_table_.end());
DCHECK(it->second.busy);
it->second.busy = false; // For the sake of a |DCHECK()|.
handle_table_.erase(it);
}
} else {
base::AutoLock locker(handle_table_lock_);
// Failed, so the handles should go back to their normal state.
for (uint32_t i = 0; i < num_handles; i++) {
HandleTableMap::iterator it = handle_table_.find(handles[i]);
DCHECK(it != handle_table_.end());
DCHECK(it->second.busy);
it->second.busy = false;
}
}
return rv;
}
MojoResult CoreImpl::ReadMessage(
MojoHandle handle,
void* bytes, uint32_t* num_bytes,
MojoHandle* handles, uint32_t* num_handles,
MojoReadMessageFlags flags) {
scoped_refptr<Dispatcher> dispatcher(GetDispatcher(handle));
if (!dispatcher.get())
return MOJO_RESULT_INVALID_ARGUMENT;
if (num_handles) {
if (!VerifyUserPointer<uint32_t>(num_handles, 1))
return MOJO_RESULT_INVALID_ARGUMENT;
if (!VerifyUserPointer<MojoHandle>(handles, *num_handles))
return MOJO_RESULT_INVALID_ARGUMENT;
}
// Easy case: won't receive any handles.
if (!num_handles || *num_handles == 0)
return dispatcher->ReadMessage(bytes, num_bytes, 0, NULL, flags);
std::vector<scoped_refptr<Dispatcher> > dispatchers;
MojoResult rv = dispatcher->ReadMessage(bytes, num_bytes,
&dispatchers, num_handles,
flags);
if (!dispatchers.empty()) {
DCHECK_EQ(rv, MOJO_RESULT_OK);
DCHECK(num_handles);
DCHECK_LE(dispatchers.size(), static_cast<size_t>(*num_handles));
base::AutoLock locker(handle_table_lock_);
for (size_t i = 0; i < dispatchers.size(); i++) {
// TODO(vtl): What should we do if we hit the maximum handle table size
// here? Currently, we'll just fill in those handles with
// |MOJO_HANDLE_INVALID| (and return success anyway).
handles[i] = AddDispatcherNoLock(dispatchers[i]);
}
}
return rv;
}
CoreImpl::CoreImpl()
: next_handle_(MOJO_HANDLE_INVALID + 1) {
}
CoreImpl::~CoreImpl() {
// This should usually not be reached (the singleton lives forever), except
// in tests.
}
scoped_refptr<Dispatcher> CoreImpl::GetDispatcher(MojoHandle handle) {
if (handle == MOJO_HANDLE_INVALID)
return NULL;
base::AutoLock locker(handle_table_lock_);
HandleTableMap::iterator it = handle_table_.find(handle);
if (it == handle_table_.end())
return NULL;
return it->second.dispatcher;
}
MojoHandle CoreImpl::AddDispatcherNoLock(
const scoped_refptr<Dispatcher>& dispatcher) {
DCHECK(dispatcher.get());
handle_table_lock_.AssertAcquired();
DCHECK_NE(next_handle_, MOJO_HANDLE_INVALID);
if (handle_table_.size() >= kMaxHandleTableSize)
return MOJO_HANDLE_INVALID;
// TODO(vtl): Maybe we want to do something different/smarter. (Or maybe try
// assigning randomly?)
while (handle_table_.find(next_handle_) != handle_table_.end()) {
next_handle_++;
if (next_handle_ == MOJO_HANDLE_INVALID)
next_handle_++;
}
MojoHandle new_handle = next_handle_;
handle_table_[new_handle] = HandleTableEntry(dispatcher);
next_handle_++;
if (next_handle_ == MOJO_HANDLE_INVALID)
next_handle_++;
return new_handle;
}
// Note: We allow |handles| to repeat the same handle multiple times, since
// different flags may be specified.
// TODO(vtl): This incurs a performance cost in |RemoveWaiter()|. Analyze this
// more carefully and address it if necessary.
MojoResult CoreImpl::WaitManyInternal(const MojoHandle* handles,
const MojoWaitFlags* flags,
uint32_t num_handles,
MojoDeadline deadline) {
DCHECK_GT(num_handles, 0u);
std::vector<scoped_refptr<Dispatcher> > dispatchers;
dispatchers.reserve(num_handles);
for (uint32_t i = 0; i < num_handles; i++) {
scoped_refptr<Dispatcher> dispatcher = GetDispatcher(handles[i]);
if (!dispatcher.get())
return MOJO_RESULT_INVALID_ARGUMENT;
dispatchers.push_back(dispatcher);
}
// TODO(vtl): Should make the waiter live (permanently) in TLS.
Waiter waiter;
waiter.Init();
uint32_t i;
MojoResult rv = MOJO_RESULT_OK;
for (i = 0; i < num_handles; i++) {
rv = dispatchers[i]->AddWaiter(&waiter,
flags[i],
static_cast<MojoResult>(i));
if (rv != MOJO_RESULT_OK)
break;
}
uint32_t num_added = i;
if (rv == MOJO_RESULT_ALREADY_EXISTS)
rv = static_cast<MojoResult>(i); // The i-th one is already "triggered".
else if (rv == MOJO_RESULT_OK)
rv = waiter.Wait(deadline);
// Make sure no other dispatchers try to wake |waiter| for the current
// |Wait()|/|WaitMany()| call. (Only after doing this can |waiter| be
// destroyed, but this would still be required if the waiter were in TLS.)
for (i = 0; i < num_added; i++)
dispatchers[i]->RemoveWaiter(&waiter);
return rv;
}
} // namespace system
} // namespace mojo