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// Copyright (c) 2006-2008 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.
#ifndef SANDBOX_SRC_SHAREDMEM_IPC_CLIENT_H__
#define SANDBOX_SRC_SHAREDMEM_IPC_CLIENT_H__
#include "sandbox/win/src/crosscall_params.h"
#include "sandbox/win/src/sandbox.h"
// IPC transport implementation that uses shared memory.
// This is the client side
//
// The shared memory is divided on blocks called channels, and potentially
// it can perform as many concurrent IPC calls as channels. The IPC over
// each channel is strictly synchronous for the client.
//
// Each channel as a channel control section associated with. Each control
// section has two kernel events (known as ping and pong) and a integer
// variable that maintains a state
//
// this is the state diagram of a channel:
//
// locked in service
// kFreeChannel---------->BusyChannel-------------->kAckChannel
// ^ |
// |_________________________________________________|
// answer ready
//
// The protocol is as follows:
// 1) client finds a free channel: state = kFreeChannel
// 2) does an atomic compare-and-swap, now state = BusyChannel
// 3) client writes the data into the channel buffer
// 4) client signals the ping event and waits (blocks) on the pong event
// 5) eventually the server signals the pong event
// 6) the client awakes and reads the answer from the same channel
// 7) the client updates its InOut parameters with the new data from the
// shared memory section.
// 8) the client atomically sets the state = kFreeChannel
//
// In the shared memory the layout is as follows:
//
// [ channel count ]
// [ channel control 0]
// [ channel control 1]
// [ channel control N]
// [ channel buffer 0 ] 1024 bytes
// [ channel buffer 1 ] 1024 bytes
// [ channel buffer N ] 1024 bytes
//
// By default each channel buffer is 1024 bytes
namespace sandbox {
// the possible channel states as described above
enum ChannelState {
// channel is free
kFreeChannel = 1,
// IPC in progress client side
kBusyChannel,
// IPC in progress server side
kAckChannel,
// not used right now
kReadyChannel,
// IPC abandoned by client side
kAbandonedChannel
};
// The next two constants control the time outs for the IPC.
const DWORD kIPCWaitTimeOut1 = 1000; // Milliseconds.
const DWORD kIPCWaitTimeOut2 = 50; // Milliseconds.
// the channel control structure
struct ChannelControl {
// points to be beginning of the channel buffer, where data goes
size_t channel_base;
// maintains the state from the ChannelState enumeration
volatile LONG state;
// the ping event is signaled by the client when the IPC data is ready on
// the buffer
HANDLE ping_event;
// the client waits on the pong event for the IPC answer back
HANDLE pong_event;
// the IPC unique identifier
uint32 ipc_tag;
};
struct IPCControl {
// total number of channels available, some might be busy at a given time
size_t channels_count;
// handle to a shared mutex to detect when the server is dead
HANDLE server_alive;
// array of channel control structures
ChannelControl channels[1];
};
// the actual shared memory IPC implementation class. This object is designed
// to be lightweight so it can be constructed on-site (at the calling place)
// wherever an IPC call is needed.
class SharedMemIPCClient {
public:
// Creates the IPC client.
// as parameter it takes the base address of the shared memory
explicit SharedMemIPCClient(void* shared_mem);
// locks a free channel and returns the channel buffer memory base. This call
// blocks until there is a free channel
void* GetBuffer();
// releases the lock on the channel, for other to use. call this if you have
// called GetBuffer and you want to abort but have not called yet DoCall()
void FreeBuffer(void* buffer);
// Performs the actual IPC call.
// params: The blob of packed input parameters.
// answer: upon IPC completion, it contains the server answer to the IPC.
// If the return value is not SBOX_ERROR_CHANNEL_ERROR, the caller has to free
// the channel.
// returns ALL_OK if the IPC mechanism successfully delivered. You still need
// to check on the answer structure to see the actual IPC result.
ResultCode DoCall(CrossCallParams* params, CrossCallReturn* answer);
private:
// Returns the index of the first free channel. It sets 'severe_failure'
// to true if there is an unrecoverable error that does not allow to
// find a channel.
size_t LockFreeChannel(bool* severe_failure);
// Return the channel index given the address of the buffer.
size_t ChannelIndexFromBuffer(const void* buffer);
IPCControl* control_;
// point to the first channel base
char* first_base_;
};
} // namespace sandbox
#endif // SANDBOX_SRC_SHAREDMEM_IPC_CLIENT_H__
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