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// Copyright (C) 2015-2021 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef PROCESS_SPAWN_H
#define PROCESS_SPAWN_H
#include <asiolink/io_service.h>
#include <exceptions/exceptions.h>
#include <boost/noncopyable.hpp>
#include <string>
#include <sys/types.h>
#include <vector>
#include <boost/shared_ptr.hpp>
namespace isc {
namespace asiolink {
/// @brief Exception thrown when error occurs during spawning a process.
class ProcessSpawnError : public Exception {
public:
ProcessSpawnError(const char* file, size_t line, const char* what) :
isc::Exception(file, line, what) { };
};
/// @brief Forward declaration to the implementation of the @c ProcessSpawn
/// class.
class ProcessSpawnImpl;
/// @brief Pointer to a ProcessSpawnImpl class.
typedef boost::shared_ptr<ProcessSpawnImpl> ProcessSpawnImplPtr;
/// @brief Type of the container holding arguments of the executable
/// being run as a background process.
typedef std::vector<std::string> ProcessArgs;
/// @brief Type of the container holding environment variables of the executable
/// being run as a background process.
typedef std::vector<std::string> ProcessEnvVars;
/// @brief Utility class for spawning new processes.
///
/// This class is used to spawn new process by Kea. It forks the current
/// process and then uses the @c execve function to execute the specified
/// binary with parameters. The @c ProcessSpawn installs the handler for
/// the SIGCHLD signal, which is executed when the child process ends.
/// The handler checks the exit code returned by the process and records
/// it. The exit code can be retrieved by the caller using the
/// @c ProcessSpawn::getExitStatus method.
///
/// This class is made noncopyable so that we don't have attempts
/// to make multiple copies of an object. This avoid problems
/// with multiple copies of objects for a single global resource
/// such as the SIGCHLD signal handler. In addition making it
/// noncopyable keeps the static check code from flagging the
/// lack of a copy constructor as an issue.
///
/// @note The ProcessSpawn uses full path for the program to execute.
class ProcessSpawn : boost::noncopyable {
public:
/// @brief Constructor.
///
/// @param io_service The IOService which handles signal handlers.
/// @param executable A full path to the program to be executed.
/// @param args Arguments for the program to be executed.
/// @param vars Environment variables for the program to be executed.
ProcessSpawn(isc::asiolink::IOServicePtr io_service,
const std::string& executable,
const ProcessArgs& args = ProcessArgs(),
const ProcessEnvVars& vars = ProcessEnvVars());
/// @brief Destructor.
~ProcessSpawn() = default;
/// @brief Returns full command line, including arguments, for the process.
std::string getCommandLine() const;
/// @brief Spawn the new process.
///
/// This method forks the current process and executes the specified
/// binary with arguments within the child process.
///
/// The child process will return EXIT_FAILURE if the method was unable
/// to start the executable, e.g. as a result of insufficient permissions
/// or when the executable does not exist. If the process ends successfully
/// the EXIT_SUCCESS is returned.
///
/// @param dismiss The flag which indicated if the process status can be
/// disregarded.
/// @throw ProcessSpawnError if forking a current process failed.
pid_t spawn(bool dismiss = false);
/// @brief Checks if the process is still running.
///
/// Note that only a negative (false) result is reliable as the child
/// process can exit between the time its state is checked and this
/// function returns.
///
/// @param pid ID of the child processes for which state should be checked.
///
/// @return true if the child process is running, false otherwise.
bool isRunning(const pid_t pid) const;
/// @brief Checks if any of the spawned processes is still running.
///
/// @return true if at least one child process is still running.
bool isAnyRunning() const;
/// @brief Returns exit status of the process.
///
/// If the process is still running, the previous status is returned
/// or 0, if the process is being ran for the first time.
///
/// @note @c ProcessSpawn::isRunning should be called and have returned
/// false before using @c ProcessSpawn::getExitStatus.
///
/// @param pid ID of the child process for which exit status should be
/// returned.
///
/// @return Exit code of the process.
int getExitStatus(const pid_t pid) const;
/// @brief Removes the status of the process with a specified PID.
///
/// This method removes the status of the process with a specified PID.
/// If the process is still running, the status is not removed and the
/// exception is thrown.
///
/// Note @c ProcessSpawn::isRunning must be called and have returned
/// false before using clearState(). And of course
/// @c ProcessSpawn::getExitStatus should be called first, if there is
/// some interest in the status.
///
/// @param pid A process pid.
void clearState(const pid_t pid);
private:
/// @brief A smart pointer to the implementation of this class.
ProcessSpawnImplPtr impl_;
};
} // namespace asiolink
} // namespace isc
#endif // PROCESS_SPAWN_H
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