fish-shell/src/event.cpp

/** \file event.c

  Functions for handling event triggers

*/
#include "config.h" // IWYU pragma: keep

#include <signal.h>
#include <algorithm>
#include <assert.h>
#include <stddef.h>
#include <string>

#include "fallback.h" // IWYU pragma: keep
#include "wutil.h" // IWYU pragma: keep - needed for gettext
#include "input_common.h"
#include "proc.h"
#include "parser.h"
#include "common.h"
#include "event.h"
#include "signal.h"
#include "io.h"


/**
   Number of signals that can be queued before an overflow occurs
*/
#define SIG_UNHANDLED_MAX 64

/**
   This struct contains a list of generated signals waiting to be
   dispatched
*/
typedef struct
{
    /**
       Number of delivered signals
    */
    volatile int count;
    /**
       Whether signals have been skipped
    */
    volatile int overflow;
    /**
       Array of signal events
    */
    volatile int signal[SIG_UNHANDLED_MAX];
}
signal_list_t;

/**
  The signal event list. Actually two separate lists. One which is
  active, which is the one that new events is written to. The inactive
  one contains the events that are currently beeing performed.
*/
static signal_list_t sig_list[2]= {{},{}};

/**
   The index of sig_list that is the list of signals currently written to
*/
static volatile int active_list=0;

typedef std::vector<event_t *> event_list_t;

/**
   List of event handlers.
*/
static event_list_t s_event_handlers;
/**
   List of event handlers that should be removed
*/
static event_list_t killme;

/**
   List of events that have been sent but have not yet been delivered because they are blocked.
*/
static event_list_t blocked;

/** Variables (one per signal) set when a signal is observed. This is inspected by a signal handler. */
static volatile bool s_observed_signals[NSIG] = {};
static void set_signal_observed(int sig, bool val)
{
    ASSERT_IS_MAIN_THREAD();
    if (sig >= 0 && (size_t)sig < sizeof s_observed_signals / sizeof *s_observed_signals)
    {
        s_observed_signals[sig] = val;
    }
}

/**
   Tests if one event instance matches the definition of a event
   class. If both the class and the instance name a function,
   they must name the same function.

*/
static int event_match(const event_t &classv, const event_t &instance)
{

    /* If the function names are both non-empty and different, then it's not a match */
    if (! classv.function_name.empty() &&
            ! instance.function_name.empty() &&
            classv.function_name != instance.function_name)
    {
        return 0;
    }

    if (classv.type == EVENT_ANY)
        return 1;

    if (classv.type != instance.type)
        return 0;


    switch (classv.type)
    {

        case EVENT_SIGNAL:
            if (classv.param1.signal == EVENT_ANY_SIGNAL)
                return 1;
            return classv.param1.signal == instance.param1.signal;

        case EVENT_VARIABLE:
            return instance.str_param1 == classv.str_param1;

        case EVENT_EXIT:
            if (classv.param1.pid == EVENT_ANY_PID)
                return 1;
            return classv.param1.pid == instance.param1.pid;

        case EVENT_JOB_ID:
            return classv.param1.job_id == instance.param1.job_id;

        case EVENT_GENERIC:
            return instance.str_param1 == classv.str_param1;

    }

    /**
       This should never be reached
    */
    debug(0, "Warning: Unreachable code reached in event_match in event.cpp\n");
    return 0;
}



/**
   Test if specified event is blocked
*/
static int event_is_blocked(const event_t &e)
{
    const block_t *block;
    parser_t &parser = parser_t::principal_parser();

    size_t idx = 0;
    while ((block = parser.block_at_index(idx++)))
    {
        if (event_block_list_blocks_type(block->event_blocks, e.type))
            return true;

    }
    return event_block_list_blocks_type(parser.global_event_blocks, e.type);
}

wcstring event_get_desc(const event_t &e)
{

    wcstring result;
    switch (e.type)
    {

        case EVENT_SIGNAL:
            result = format_string(_(L"signal handler for %ls (%ls)"), sig2wcs(e.param1.signal), signal_get_desc(e.param1.signal));
            break;

        case EVENT_VARIABLE:
            result = format_string(_(L"handler for variable '%ls'"), e.str_param1.c_str());
            break;

        case EVENT_EXIT:
            if (e.param1.pid > 0)
            {
                result = format_string(_(L"exit handler for process %d"), e.param1.pid);
            }
            else
            {
                job_t *j = job_get_from_pid(-e.param1.pid);
                if (j)
                    result = format_string(_(L"exit handler for job %d, '%ls'"), j->job_id, j->command_wcstr());
                else
                    result = format_string(_(L"exit handler for job with process group %d"), -e.param1.pid);
            }

            break;

        case EVENT_JOB_ID:
        {
            job_t *j = job_get(e.param1.job_id);
            if (j)
                result = format_string(_(L"exit handler for job %d, '%ls'"), j->job_id, j->command_wcstr());
            else
                result = format_string(_(L"exit handler for job with job id %d"), e.param1.job_id);

            break;
        }

        case EVENT_GENERIC:
            result = format_string(_(L"handler for generic event '%ls'"), e.str_param1.c_str());
            break;

        default:
            result = format_string(_(L"Unknown event type '0x%x'"), e.type);
            break;

    }

    return result;
}

#if 0
static void show_all_handlers(void)
{
    puts("event handlers:");
    for (event_list_t::const_iterator iter = events.begin(); iter != events.end(); ++iter)
    {
        const event_t *foo = *iter;
        wcstring tmp = event_get_desc(foo);
        printf("    handler now %ls\n", tmp.c_str());
    }
}
#endif

/*
    Give a more condensed description of \c event compared to \c event_get_desc.
    It includes what function will fire if the \c event is an event handler.
 */
static wcstring event_desc_compact(const event_t &event)
{
    wcstring res;
    wchar_t const *temp;
    int sig;
    switch (event.type)
    {
        case EVENT_ANY:
            res = L"EVENT_ANY";
            break;
        case EVENT_VARIABLE:
            if (event.str_param1.c_str())
            {
                res = format_string(L"EVENT_VARIABLE($%ls)", event.str_param1.c_str());
            }
            else
            {
                res = L"EVENT_VARIABLE([any])";
            }
            break;
        case EVENT_SIGNAL:
            sig = event.param1.signal;
            if (sig == EVENT_ANY_SIGNAL)
            {
                temp = L"[all signals]";
            }
            else if (sig == 0)
            {
                temp = L"not set";
            }
            else
            {
                temp = sig2wcs(sig);
            }
            res = format_string(L"EVENT_SIGNAL(%ls)", temp);
            break;
        case EVENT_EXIT:
            if (event.param1.pid == EVENT_ANY_PID)
            {
                res = wcstring(L"EVENT_EXIT([all child processes])");
            }
            else if (event.param1.pid > 0)
            {
                res = format_string(L"EVENT_EXIT(pid %d)", event.param1.pid);
            }
            else
            {
                job_t *j = job_get_from_pid(-event.param1.pid);
                if (j)
                    res = format_string(L"EVENT_EXIT(jobid %d: \"%ls\")", j->job_id, j->command_wcstr());
                else
                    res = format_string(L"EVENT_EXIT(pgid %d)", -event.param1.pid);
            }
            break;
        case EVENT_JOB_ID:
        {
            job_t *j = job_get(event.param1.job_id);
            if (j)
                res = format_string(L"EVENT_JOB_ID(job %d: \"%ls\")", j->job_id, j->command_wcstr());
            else
                res = format_string(L"EVENT_JOB_ID(jobid %d)", event.param1.job_id);
            break;
        }
        case EVENT_GENERIC:
            res = format_string(L"EVENT_GENERIC(%ls)", event.str_param1.c_str());
            break;
        default:
            res = format_string(L"unknown/illegal event(%x)", event.type);
    }
    if (event.function_name.size())
    {
        return format_string(L"%ls: \"%ls\"", res.c_str(), event.function_name.c_str());
    }
    else
    {
        return res;
    }
}


void event_add_handler(const event_t &event)
{
    event_t *e;

    if (debug_level >= 3)
    {
        wcstring desc = event_desc_compact(event);
        debug(3, "register: %ls\n", desc.c_str());
    }

    e = new event_t(event);

    if (e->type == EVENT_SIGNAL)
    {
        signal_handle(e->param1.signal, 1);
        set_signal_observed(e->param1.signal, true);
    }

    s_event_handlers.push_back(e);
}

void event_remove(const event_t &criterion)
{
    event_list_t new_list;

    if (debug_level >= 3)
    {
        wcstring desc = event_desc_compact(criterion);
        debug(3, "unregister: %ls\n", desc.c_str());
    }

    /*
      Because of concurrency issues (env_remove could remove an event
      that is currently being executed), env_remove does not actually
      free any events - instead it simply moves all events that should
      be removed from the event list to the killme list, and the ones
      that shouldn't be killed to new_list, and then drops the empty
      events-list.
    */

    if (s_event_handlers.empty())
        return;

    for (size_t i=0; i<s_event_handlers.size(); i++)
    {
        event_t *n = s_event_handlers.at(i);
        if (event_match(criterion, *n))
        {
            killme.push_back(n);

            /*
              If this event was a signal handler and no other handler handles
              the specified signal type, do not handle that type of signal any
              more.
            */
            if (n->type == EVENT_SIGNAL)
            {
                event_t e = event_t::signal_event(n->param1.signal);
                if (event_get(e, 0) == 1)
                {
                    signal_handle(e.param1.signal, 0);
                    set_signal_observed(e.param1.signal, 0);
                }
            }
        }
        else
        {
            new_list.push_back(n);
        }
    }
    s_event_handlers.swap(new_list);
}

int event_get(const event_t &criterion, std::vector<event_t *> *out)
{
    int found = 0;
    for (size_t i=0; i < s_event_handlers.size(); i++)
    {
        event_t *n = s_event_handlers.at(i);
        if (event_match(criterion, *n))
        {
            found++;
            if (out)
                out->push_back(n);
        }
    }
    return found;
}

bool event_is_signal_observed(int sig)
{
    /* We are in a signal handler! Don't allocate memory, etc.
    */
    bool result = false;
    if (sig >= 0 && sig < sizeof s_observed_signals / sizeof *s_observed_signals)
    {
        result = s_observed_signals[sig];
    }
    return result;
}

/**
   Free all events in the kill list
*/
static void event_free_kills()
{
    for_each(killme.begin(), killme.end(), event_free);
    killme.resize(0);
}

/**
   Test if the specified event is waiting to be killed
*/
static int event_is_killed(const event_t &e)
{
    return std::find(killme.begin(), killme.end(), &e) != killme.end();
}

/* Callback for firing (and then deleting) an event */
static void fire_event_callback(void *arg)
{
    ASSERT_IS_MAIN_THREAD();
    assert(arg != NULL);
    event_t *event = static_cast<event_t *>(arg);
    event_fire(event);
    delete event;
}

/**
   Perform the specified event. Since almost all event firings will
   not be matched by even a single event handler, we make sure to
   optimize the 'no matches' path. This means that nothing is
   allocated/initialized unless needed.
*/
static void event_fire_internal(const event_t &event)
{

    event_list_t fire;

    /*
      First we free all events that have been removed, but only if this
    		invocation of event_fire_internal is not a recursive call.
    */
    if (is_event <= 1)
        event_free_kills();

    if (s_event_handlers.empty())
        return;

    /*
      Then we iterate over all events, adding events that should be
      fired to a second list. We need to do this in a separate step
      since an event handler might call event_remove or
      event_add_handler, which will change the contents of the \c
      events list.
    */
    for (size_t i=0; i<s_event_handlers.size(); i++)
    {
        event_t *criterion = s_event_handlers.at(i);

        /*
          Check if this event is a match
        */
        if (event_match(*criterion, event))
        {
            fire.push_back(criterion);
        }
    }

    /*
      No matches. Time to return.
    */
    if (fire.empty())
        return;

    if (signal_is_blocked())
    {
        /* Fix for https://github.com/fish-shell/fish-shell/issues/608. Don't run event handlers while signals are blocked. */
        event_t *heap_event = new event_t(event);
        input_common_add_callback(fire_event_callback, heap_event);
        return;
    }

    /*
      Iterate over our list of matching events
    */

    for (size_t i=0; i<fire.size(); i++)
    {
        event_t *criterion = fire.at(i);
        int prev_status;

        /*
          Check if this event has been removed, if so, dont fire it
        */
        if (event_is_killed(*criterion))
            continue;

        /*
          Fire event
        */
        wcstring buffer = criterion->function_name;

        for (size_t j=0; j < event.arguments.size(); j++)
        {
            wcstring arg_esc = escape_string(event.arguments.at(j), 1);
            buffer += L" ";
            buffer += arg_esc;
        }

        // debug( 1, L"Event handler fires command '%ls'", buffer.c_str() );

        /*
          Event handlers are not part of the main flow of code, so
          they are marked as non-interactive
        */
        proc_push_interactive(0);
        prev_status = proc_get_last_status();
        parser_t &parser = parser_t::principal_parser();

        block_t *block = new event_block_t(event);
        parser.push_block(block);
        parser.eval(buffer, io_chain_t(), TOP);
        parser.pop_block();
        proc_pop_interactive();
        proc_set_last_status(prev_status);
    }

    /*
      Free killed events
    */
    if (is_event <= 1)
        event_free_kills();

}

/**
   Handle all pending signal events
*/
static void event_fire_delayed()
{
    /*
      If is_event is one, we are running the event-handler non-recursively.

      When the event handler has called a piece of code that triggers
      another event, we do not want to fire delayed events because of
      concurrency problems.
    */
    if (! blocked.empty() && is_event==1)
    {
        event_list_t new_blocked;

        for (size_t i=0; i<blocked.size(); i++)
        {
            event_t *e = blocked.at(i);
            if (event_is_blocked(*e))
            {
                new_blocked.push_back(new event_t(*e));
            }
            else
            {
                event_fire_internal(*e);
                event_free(e);
            }
        }
        blocked.swap(new_blocked);
    }

    int al = active_list;

    while (sig_list[al].count > 0)
    {
        signal_list_t *lst;

        /*
          Switch signal lists
        */
        sig_list[1-al].count=0;
        sig_list[1-al].overflow=0;
        al = 1-al;
        active_list=al;

        /*
          Set up
        */
        lst = &sig_list[1-al];
        event_t e = event_t::signal_event(0);
        e.arguments.resize(1);

        if (lst->overflow)
        {
            debug(0, _(L"Signal list overflow. Signals have been ignored."));
        }

        /*
          Send all signals in our private list
        */
        for (int i=0; i < lst->count; i++)
        {
            e.param1.signal = lst->signal[i];
            e.arguments.at(0) = sig2wcs(e.param1.signal);
            if (event_is_blocked(e))
            {
                blocked.push_back(new event_t(e));
            }
            else
            {
                event_fire_internal(e);
            }
        }

    }
}

void event_fire_signal(int signal)
{
    /*
      This means we are in a signal handler. We must be very
      careful not do do anything that could cause a memory
      allocation or something else that might be bad when in a
      signal handler.
    */
    if (sig_list[active_list].count < SIG_UNHANDLED_MAX)
        sig_list[active_list].signal[sig_list[active_list].count++]=signal;
    else
        sig_list[active_list].overflow=1;
}


void event_fire(const event_t *event)
{

    if (event && event->type == EVENT_SIGNAL)
    {
        event_fire_signal(event->param1.signal);
    }
    else
    {
        is_event++;

        /*
          Fire events triggered by signals
        */
        event_fire_delayed();

        if (event)
        {
            if (event_is_blocked(*event))
            {
                blocked.push_back(new event_t(*event));
            }
            else
            {
                event_fire_internal(*event);
            }
        }
        is_event--;
    }
}


void event_init()
{
}

void event_destroy()
{

    for_each(s_event_handlers.begin(), s_event_handlers.end(), event_free);
    s_event_handlers.clear();

    for_each(killme.begin(), killme.end(), event_free);
    killme.clear();
}

void event_free(event_t *e)
{
    CHECK(e,);
    delete e;
}

void event_fire_generic(const wchar_t *name, wcstring_list_t *args)
{
    CHECK(name,);

    event_t ev(EVENT_GENERIC);
    ev.str_param1 = name;
    if (args)
        ev.arguments = *args;
    event_fire(&ev);
}

event_t::event_t(int t) : type(t), param1(), str_param1(), function_name(), arguments()
{
}

event_t::~event_t()
{
}

event_t event_t::signal_event(int sig)
{
    event_t event(EVENT_SIGNAL);
    event.param1.signal = sig;
    return event;
}

event_t event_t::variable_event(const wcstring &str)
{
    event_t event(EVENT_VARIABLE);
    event.str_param1 = str;
    return event;
}

event_t event_t::generic_event(const wcstring &str)
{
    event_t event(EVENT_GENERIC);
    event.str_param1 = str;
    return event;
}