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#include "signals.hh"
#include "error.hh"
#include "sync.hh"
#include "terminal.hh"
#include <map>
#include <thread>
namespace nix {
std::atomic<bool> _isInterrupted = false;
thread_local std::function<bool()> interruptCheck;
void _interrupted()
{
/* Block user interrupts while an exception is being handled.
Throwing an exception while another exception is being handled
kills the program! */
if (!std::uncaught_exceptions()) {
throw Interrupted("interrupted by the user");
}
}
//////////////////////////////////////////////////////////////////////
/* We keep track of interrupt callbacks using integer tokens, so we can iterate
safely without having to lock the data structure while executing arbitrary
functions.
*/
struct InterruptCallbacks {
typedef int64_t Token;
/* We use unique tokens so that we can't accidentally delete the wrong
handler because of an erroneous double delete. */
Token nextToken = 0;
/* Used as a list, see InterruptCallbacks comment. */
std::map<Token, std::function<void()>> callbacks;
};
static Sync<InterruptCallbacks> _interruptCallbacks;
static void signalHandlerThread(sigset_t set)
{
while (true) {
int signal = 0;
sigwait(&set, &signal);
if (signal == SIGINT || signal == SIGTERM || signal == SIGHUP)
triggerInterrupt();
else if (signal == SIGWINCH) {
updateWindowSize();
}
}
}
void triggerInterrupt()
{
_isInterrupted = true;
{
InterruptCallbacks::Token i = 0;
while (true) {
std::function<void()> callback;
{
auto interruptCallbacks(_interruptCallbacks.lock());
auto lb = interruptCallbacks->callbacks.lower_bound(i);
if (lb == interruptCallbacks->callbacks.end())
break;
callback = lb->second;
i = lb->first + 1;
}
try {
callback();
} catch (...) {
ignoreException();
}
}
}
}
static sigset_t savedSignalMask;
static bool savedSignalMaskIsSet = false;
void setChildSignalMask(sigset_t * sigs)
{
assert(sigs); // C style function, but think of sigs as a reference
#if _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
sigemptyset(&savedSignalMask);
// There's no "assign" or "copy" function, so we rely on (math) idempotence
// of the or operator: a or a = a.
sigorset(&savedSignalMask, sigs, sigs);
#else
// Without sigorset, our best bet is to assume that sigset_t is a type that
// can be assigned directly, such as is the case for a sigset_t defined as
// an integer type.
savedSignalMask = *sigs;
#endif
savedSignalMaskIsSet = true;
}
void saveSignalMask() {
if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask))
throw SysError("querying signal mask");
savedSignalMaskIsSet = true;
}
void startSignalHandlerThread()
{
updateWindowSize();
saveSignalMask();
sigset_t set;
sigemptyset(&set);
sigaddset(&set, SIGINT);
sigaddset(&set, SIGTERM);
sigaddset(&set, SIGHUP);
sigaddset(&set, SIGPIPE);
sigaddset(&set, SIGWINCH);
if (pthread_sigmask(SIG_BLOCK, &set, nullptr))
throw SysError("blocking signals");
std::thread(signalHandlerThread, set).detach();
}
void restoreSignals()
{
// If startSignalHandlerThread wasn't called, that means we're not running
// in a proper libmain process, but a process that presumably manages its
// own signal handlers. Such a process should call either
// - initNix(), to be a proper libmain process
// - startSignalHandlerThread(), to resemble libmain regarding signal
// handling only
// - saveSignalMask(), for processes that define their own signal handling
// thread
// TODO: Warn about this? Have a default signal mask? The latter depends on
// whether we should generally inherit signal masks from the caller.
// I don't know what the larger unix ecosystem expects from us here.
if (!savedSignalMaskIsSet)
return;
if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
throw SysError("restoring signals");
}
/* RAII helper to automatically deregister a callback. */
struct InterruptCallbackImpl : InterruptCallback
{
InterruptCallbacks::Token token;
~InterruptCallbackImpl() override
{
auto interruptCallbacks(_interruptCallbacks.lock());
interruptCallbacks->callbacks.erase(token);
}
};
std::unique_ptr<InterruptCallback> createInterruptCallback(std::function<void()> callback)
{
auto interruptCallbacks(_interruptCallbacks.lock());
auto token = interruptCallbacks->nextToken++;
interruptCallbacks->callbacks.emplace(token, callback);
auto res = std::make_unique<InterruptCallbackImpl>();
res->token = token;
return std::unique_ptr<InterruptCallback>(res.release());
}
};
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