Related
I know I can set thread name (the one visible in gdb and htop) in Linux using prctl(). But with another OSes this most likely won't work. Also, I could try using pthread_setname_np(), which is a bit more available across POSIX systems, but still lacks full compatibility.
So I'd like to have some more portable way, maybe something QThread provides which I've not found. Is there any such way?
There's nothing in the QThread API to manually manage the system name of the thread, however, since version 4.8.3, Qt will automatically set the name of your thread to the name of the thread object (QObject::objectName()).
This is handled in the implementations of QThread as described below.
You have something like this in qthread_unix.cpp:
#if (defined(Q_OS_LINUX) || defined(Q_OS_MAC) || defined(Q_OS_QNX))
static void setCurrentThreadName(pthread_t threadId, const char *name)
{
# if defined(Q_OS_LINUX) && !defined(QT_LINUXBASE)
Q_UNUSED(threadId);
prctl(PR_SET_NAME, (unsigned long)name, 0, 0, 0);
# elif defined(Q_OS_MAC)
Q_UNUSED(threadId);
pthread_setname_np(name);
# elif defined(Q_OS_QNX)
pthread_setname_np(threadId, name);
# endif
}
#endif
/*
* [...]
*/
QString objectName = thr->objectName();
if (Q_LIKELY(objectName.isEmpty()))
setCurrentThreadName(thr->d_func()->thread_id, thr->metaObject()->className());
else
setCurrentThreadName(thr->d_func()->thread_id, objectName.toLocal8Bit());
And the equivalent in qthread_win.cpp:
typedef struct tagTHREADNAME_INFO
{
DWORD dwType; // must be 0x1000
LPCSTR szName; // pointer to name (in user addr space)
HANDLE dwThreadID; // thread ID (-1=caller thread)
DWORD dwFlags; // reserved for future use, must be zero
} THREADNAME_INFO;
void qt_set_thread_name(HANDLE threadId, LPCSTR threadName)
{
THREADNAME_INFO info;
info.dwType = 0x1000;
info.szName = threadName;
info.dwThreadID = threadId;
info.dwFlags = 0;
__try
{
RaiseException(0x406D1388, 0, sizeof(info)/sizeof(DWORD), (const ULONG_PTR*)&info);
}
__except (EXCEPTION_CONTINUE_EXECUTION)
{
}
}
/*
* [...]
*/
QByteArray objectName = thr->objectName().toLocal8Bit();
qt_set_thread_name((HANDLE)-1, objectName.isEmpty() ? thr->metaObject()->className() : objectName.constData());
Note that on Windows, the above code won't be executed if QT_NO_DEBUG is set, thus it won't work in Release mode.
In Qt documentation you can find:
To choose the name that your thread will be given (as identified by
the command ps -L on Linux, for example), you can call setObjectName()
before starting the thread. If you don't call setObjectName(), the
name given to your thread will be the class name of the runtime type
of your thread object (for example, "RenderThread" in the case of the
Mandelbrot Example, as that is the name of the QThread subclass). Note
that this is currently not available with release builds on Windows.
I'm trying to write some code to communicate with wpa_supplicant using DBUS. As I'm working in an embedded system (ARM), I'd like to avoid the use of Python or the GLib. I'm wondering if I'm stupid because I really have the feeling that there is no nice and clear documentation about D-Bus. Even with the official one, I either find the documentation too high level, or the examples shown are using Glib! Documentation I've looked at: http://www.freedesktop.org/wiki/Software/dbus
I found a nice article about using D-Bus in C: http://www.matthew.ath.cx/articles/dbus
However, this article is pretty old and not complete enough! I also found the c++-dbus API but also here, I don't find ANY documentation! I've been digging into wpa_supplicant and NetworkManager source code but it's quite a nightmare! I've been looking into the "low-level D-Bus API" as well but this doesn't tell me how to extract a string parameter from a D-Bus message! http://dbus.freedesktop.org/doc/api/html/index.html
Here is some code I wrote to test a little but I really have trouble to extract string values. Sorry for the long source code but if someone want to try it ... My D-Bus configuration seems fine because it "already" catches "StateChanged" signals from wpa_supplicant but cannot print the state:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <dbus/dbus.h>
//#include "wpa_supp_dbus.h"
/* Content of wpa_supp_dbus.h */
#define WPAS_DBUS_SERVICE "fi.epitest.hostap.WPASupplicant"
#define WPAS_DBUS_PATH "/fi/epitest/hostap/WPASupplicant"
#define WPAS_DBUS_INTERFACE "fi.epitest.hostap.WPASupplicant"
#define WPAS_DBUS_PATH_INTERFACES WPAS_DBUS_PATH "/Interfaces"
#define WPAS_DBUS_IFACE_INTERFACE WPAS_DBUS_INTERFACE ".Interface"
#define WPAS_DBUS_NETWORKS_PART "Networks"
#define WPAS_DBUS_IFACE_NETWORK WPAS_DBUS_INTERFACE ".Network"
#define WPAS_DBUS_BSSIDS_PART "BSSIDs"
#define WPAS_DBUS_IFACE_BSSID WPAS_DBUS_INTERFACE ".BSSID"
int running = 1;
void stopLoop(int sig)
{
running = 0;
}
void sendScan()
{
// TODO !
}
void loop(DBusConnection* conn)
{
DBusMessage* msg;
DBusMessageIter args;
DBusMessageIter subArgs;
int argType;
int i;
int buffSize = 1024;
char strValue[buffSize];
const char* member = 0;
sendScan();
while (running)
{
// non blocking read of the next available message
dbus_connection_read_write(conn, 0);
msg = dbus_connection_pop_message(conn);
// loop again if we haven't read a message
if (!msg)
{
printf("No message received, waiting a little ...\n");
sleep(1);
continue;
}
else printf("Got a message, will analyze it ...\n");
// Print the message member
printf("Got message for interface %s\n",
dbus_message_get_interface(msg));
member = dbus_message_get_member(msg);
if(member) printf("Got message member %s\n", member);
// Check has argument
if (!dbus_message_iter_init(msg, &args))
{
printf("Message has no argument\n");
continue;
}
else
{
// Go through arguments
while(1)
{
argType = dbus_message_iter_get_arg_type(&args);
if (argType == DBUS_TYPE_STRING)
{
printf("Got string argument, extracting ...\n");
/* FIXME : got weird characters
dbus_message_iter_get_basic(&args, &strValue);
*/
/* FIXME : segmentation fault !
dbus_message_iter_get_fixed_array(
&args, &strValue, buffSize);
*/
/* FIXME : segmentation fault !
dbus_message_iter_recurse(&args, &subArgs);
*/
/* FIXME : deprecated!
if(dbus_message_iter_get_array_len(&args) > buffSize)
printf("message content to big for local buffer!");
*/
//printf("String value was %s\n", strValue);
}
else
printf("Arg type not implemented yet !\n");
if(dbus_message_iter_has_next(&args))
dbus_message_iter_next(&args);
else break;
}
printf("No more arguments!\n");
}
// free the message
dbus_message_unref(msg);
}
}
int main(int argc, char* argv[])
{
DBusError err;
DBusConnection* conn;
int ret;
char signalDesc[1024]; // Signal description as string
// Signal handling
signal(SIGKILL, stopLoop);
signal(SIGTERM, stopLoop);
// Initialize err struct
dbus_error_init(&err);
// connect to the bus
conn = dbus_bus_get(DBUS_BUS_SYSTEM, &err);
if (dbus_error_is_set(&err))
{
fprintf(stderr, "Connection Error (%s)\n", err.message);
dbus_error_free(&err);
}
if (!conn)
{
exit(1);
}
// request a name on the bus
ret = dbus_bus_request_name(conn, WPAS_DBUS_SERVICE, 0, &err);
if (dbus_error_is_set(&err))
{
fprintf(stderr, "Name Error (%s)\n", err.message);
dbus_error_free(&err);
}
/* Connect to signal */
// Interface signal ..
sprintf(signalDesc, "type='signal',interface='%s'",
WPAS_DBUS_IFACE_INTERFACE);
dbus_bus_add_match(conn, signalDesc, &err);
dbus_connection_flush(conn);
if (dbus_error_is_set(&err))
{
fprintf(stderr, "Match Error (%s)\n", err.message);
exit(1);
}
// Network signal ..
sprintf(signalDesc, "type='signal',interface='%s'",
WPAS_DBUS_IFACE_NETWORK);
dbus_bus_add_match(conn, signalDesc, &err);
dbus_connection_flush(conn);
if (dbus_error_is_set(&err))
{
fprintf(stderr, "Match Error (%s)\n", err.message);
exit(1);
}
// Bssid signal ..
sprintf(signalDesc, "type='signal',interface='%s'",
WPAS_DBUS_IFACE_BSSID);
dbus_bus_add_match(conn, signalDesc, &err);
dbus_connection_flush(conn);
if (dbus_error_is_set(&err))
{
fprintf(stderr, "Match Error (%s)\n", err.message);
exit(1);
}
// Do main loop
loop(conn);
// Main loop exited
printf("Main loop stopped, exiting ...\n");
dbus_connection_close(conn);
return 0;
}
Any pointer to any nice, complete, low-level C tutorial is strongly appreciated! I'm also planning to do some remote method call, so if the tutorial covers this subject it would be great! Saying I'm not very smart because I don't get it with the official tutorial is also appreciated :-p!
Or is there another way to communicate with wpa_supplicant (except using wpa_cli)?
EDIT 1:
Using 'qdbusviewer' and the introspection capabilty, this helped me a lot discovering what and how wpa_supplicant works using dbus. Hopping that this would help someone else!
Edit 2:
Will probably come when I'll find a way to read string values on D-Bus!
You have given up the tools that would help you to learn D-Bus more easily and are using the low level libdbus implementation, so maybe you deserve to be in pain. BTW, are you talking about ARM, like a cell phone ARM ? With maybe 500 Mhz and 256 MB RAM ? In this case the processor is well suited to using glib, Qt or even python. And D-Bus is most useful when you're writing asynchronous event driven code, with an integrated main loop, for example from glib, even when you're using the low level libdbus (it has functions to connect to the glib main loop, for example).
Since you're using the low level library, then documentation is what you already have:
http://dbus.freedesktop.org/doc/api/html/index.html
Also, libdbus source code is also part of the documentation:
http://dbus.freedesktop.org/doc/api/html/files.html
The main entry point for the documentation is the Modules page (in particular, the public API section):
http://dbus.freedesktop.org/doc/api/html/modules.html
For message handling, the section DBusMessage is the relevant one:
DBusMessage
There you have the documentation for functions that parse item values. In your case, you started with a dbus_message_iter_get_basic. As described in the docs, retrieving the string requires a const char ** variable, since the returned value will point to the pre-allocated string in the received message:
So for int32 it should be a "dbus_int32_t*" and for string a "const char**". The returned value is by reference and should not be freed.
So you can't define an array, because libdbus won't copy the text to your array. If you need to save the string, first get the constant string reference, then strcpy to your own array.
Then you tried to get a fixed array without moving the iterator. You need a call to the next iterator (dbus_message_iter_next) between the basic string and the fixed array. Same right before recursing into the sub iterator.
Finally, you don't call get_array_len to get the number of elements on the array. From the docs, it only returns byte counts. Instead you loop over the sub iterator using iter_next the same way you should have done with the main iterator. After you have iterated past the end of the array, dbus_message_iter_get_arg_type will return DBUS_TYPE_INVALID.
For more info, read the reference manual, don't look for a tutorial. Or just use a reasonable d-bus implementation:
https://developer.gnome.org/gio/2.36/gdbus-codegen.html
GIO's GDBus automatically creates wrappers for your d-bus calls.
http://qt-project.org/doc/qt-4.8/intro-to-dbus.html
http://dbus.freedesktop.org/doc/dbus-python/doc/tutorial.html
etc.
You don't need to use/understand working of dbus If you just need to write a C program to communicate with wpa_supplicant. I reverse engineered the wpa_cli's source code. Went through its implementation and used functions provided in wpa_ctrl.h/c. This implementation takes care of everything. You can use/modify whatever you want, build your executable and you're done!
Here's the official link to wpa_supplicant's ctrl_interface:
http://hostap.epitest.fi/wpa_supplicant/devel/ctrl_iface_page.html
I doubt this answer will still be relevant to the author of this question,
but for anybody who stumbles upon this like I did:
The situation is now better than all those years ago if you don't want to include GTK/QT in your project to access dbus.
There is dbus API in Embedded Linux Library by Intel (weird I remember it being open, maybe it is just for registered users now?)
and systemd sd-bus library now offers public API. You probably run systemd anyway unless you have a really constrained embedded system.
I have worked with GDbus, dbus-cpp and sd-bus and although I wanted a C++ library,
I found sd-bus to be the simplest and the least problematic experience.
I did not try its C++ bindings but they also look nice
#include <stdio.h>
#include <systemd/sd-bus.h>
#include <stdlib.h>
const char* wpa_service = "fi.w1.wpa_supplicant1";
const char* wpa_root_obj_path = "/fi/w1/wpa_supplicant1";
const char* wpa_root_iface = "fi.w1.wpa_supplicant1";
sd_bus_error error = SD_BUS_ERROR_NULL;
sd_bus* system_bus = NULL;
sd_event* loop = NULL;
sd_bus_message* reply = NULL;
void cleanup() {
sd_event_unref(loop);
sd_bus_unref(system_bus);
sd_bus_message_unref(reply);
sd_bus_error_free(&error);
}
void print_error(const char* msg, int code) {
fprintf(stderr, "%s %s\n", msg, strerror(-code));
exit(EXIT_FAILURE);
}
const char* get_interface(const char* iface) {
int res = sd_bus_call_method(system_bus,
wpa_service,
wpa_root_obj_path,
wpa_root_iface,
"GetInterface",
&error,
&reply,
"s",
"Ifname", "s", iface,
"Driver", "s", "nl80211");
if (res < 0) {
fprintf(stderr, "(get) error response: %s\n", error.message);
return NULL;
}
const char* iface_path;
/*
* an object path was returned in reply
* this works like an iterator, if a method returns (osu), you could call message_read_basic in succession
* with arguments SD_BUS_TYPE_OBJECT_PATH, SD_BUS_TYPE_STRING, SD_BUS_TYPE_UINT32 or you could
* call sd_bus_message_read() and provides the signature + arguments in one call
* */
res = sd_bus_message_read_basic(reply, SD_BUS_TYPE_OBJECT_PATH, &iface_path);
if (res < 0) {
print_error("getIface: ", res);
return NULL;
}
return iface_path;
}
const char* create_interface(const char* iface) {
int res = sd_bus_call_method(system_bus,
wpa_service,
wpa_root_obj_path,
wpa_root_iface,
"CreateInterface",
&error,
&reply,
"a{sv}", 2, //pass array of str:variant (dbus dictionary) with 2
//entries to CreateInterface
"Ifname", "s", iface, // "s" variant parameter contains string, then pass the value
"Driver", "s", "nl80211");
if (res < 0) {
fprintf(stderr, "(create) error response: %s\n", error.message);
return NULL;
}
const char* iface_path;
res = sd_bus_message_read_basic(reply, SD_BUS_TYPE_OBJECT_PATH, &iface_path);
if (res < 0) {
print_error("createIface: ", res);
}
return iface_path;
}
int main() {
int res;
const char* iface_path;
//open connection to system bus - default either opens or reuses existing connection as necessary
res = sd_bus_default_system(&system_bus);
if (res < 0) {
print_error("open: ", res);
}
//associate connection with event loop, again default either creates or reuses existing
res = sd_event_default(&loop);
if (res < 0) {
print_error("event: ", res);
}
// get obj. path to the wireless interface on dbus so you can call methods on it
// this is a wireless interface (e.g. your wifi dongle) NOT the dbus interface
// if you don't know the interface name in advance, you will have to read the Interfaces property of
// wpa_supplicants root interface — call Get method on org.freedesktop.DBus properties interface,
// while some libraries expose some kind of get_property convenience function sd-bus does not
const char* ifaceName = "wlp32s0f3u2";
if (!(iface_path = get_interface(ifaceName))) { //substitute your wireless iface here
// sometimes the HW is present and listed in "ip l" but dbus does not reflect that, this fixes it
if (!(iface_path = create_interface(ifaceName))) {
fprintf(stderr, "can't create iface: %s" , ifaceName);
cleanup();
return EXIT_FAILURE;
}
}
/*
call methods with obj. path iface_path and dbus interface of your choice
this will likely be "fi.w1.wpa_supplicant1.Interface", register for signals etc...
you will need the following to receive those signals
*/
int runForUsec = 1000000; //usec, not msec!
sd_event_run(loop, runForUsec); //or sd_event_loop(loop) if you want to loop forever
cleanup();
printf("Finished OK\n");
return 0;
}
I apologize if the example above does not work perfectly. It is an excerpt from an old project I rewrote to C from C++ (I think it's C(-ish), compiler does not protest and you asked for C) but I can't test it as all my dongles refuse to work with my desktop right now. It should give you a general idea though.
Note that you will likely encounter several magical or semi-magical issues.
To ensure smooth developing/testing do the following:
make sure other network management applications are disabled (networkmanager, connman...)
restart the wpa_supplicant service
make sure the wireless interface is UP in ip link
Also, because is not that well-documented right now:
You can access arrays and inner variant values by sd_bus_message_enter_container
and _exit counterpart. sd_bus_message_peek_type might come handy while doing that.
Or sd_bus_message_read_array for a homogenous array.
The below snippet works for me
if (argType == DBUS_TYPE_STRING)
{
printf("Got string argument, extracting ...\n");
char* strBuffer = NULL;
dbus_message_iter_get_basic(&args, &strBuffer);
printf("Received string: \n %s \n",strBuffer);
}
I had a perfectly working OpenCV code (having the function cvCaptureFromCAM(0)). But when I modified it to run in a separate thread, I get this "Video Source" selection dialog box and it asks me to choose the Webcam. Even though I select a cam, it appears that the function cvCaptureFromCAM(0) returns null. I also tried by passing the values 0, -1,1, CV_CAP_ANYto this function. I have a doubt that this dialog box causes this issue. Is there any way to avoid this or does anyone have any other opinion?
I've followed the following posts when debugging:
cvCreateCameraCapture returns null
OpenCV cvCaptureFromCAM returns zero
EDIT
Code structure
//header includes
CvCapture* capture =NULL;
IplImage* frame = NULL;
int main(int argc, char** argv){
DWORD qThreadID;
HANDLE ocvThread = CreateThread(0,0,startOCV, NULL,0, &qThreadID);
initGL(argc, argv);
glutMainLoop();
CloseHandle(ocvThread);
return 0;
}
void initGL(int argc, char** argv){
//Initialize GLUT
//Create the window
//etc
}
DWORD WINAPI startOCV(LPVOID vpParam){
//capture = cvCaptureFromCAM(0); //0 // CV_CAP_ANY
if ((capture = cvCaptureFromCAM(1)) == NULL){ // same as simply using assert(capture)
cerr << "!!! ERROR: vCaptureFromCAM No camera found\n";
return -1;
}
frame = cvQueryFrame(capture);
}
//other GL functions
Thanks.
Since this is a problem that only happens on Windows, an easy fix is to leave cvCaptureFromCAM(0) on the main() thread and then do the image processing stuff on a separate thread, as you intented originally.
Just declare CvCapture* capture = NULL; as a global variable so all your threads can access it.
Solved. I couldn't get rid of the above mentioned dialog box, but I avoided the error by simply duplicating the line capture = cvCaptureFromCAM(0);
capture = cvCaptureFromCAM(0);
capture = cvCaptureFromCAM(0);
It was just random. I suspect it had something to do with behavior of Thread. What's your idea?
Thanks all for contributing.
I want to know what are the files opened/access by a process. May i know how to do that? I tried to use Deviare, a free hooking api to help me, but was unable to find any useful information from their AIP lib or forum.
I only know i have to hook on to kernel32.dll and createFileW and i am not sure of how to continue.
Pls help me. Thanks in advance.
It's right. You have to hook the function CreateFileA/W in kernel32.dll to monitor the acces. Do you want to hook these APIs in your own process or in an other process?
If you want to hook functions in your own process you can use
void *DetourFunc(BYTE *src, const BYTE *dst, const int len)
{
BYTE *jmp = (BYTE*)malloc(5+len);
DWORD dwback;
VirtualProtect(src,len,PAGE_READWRITE,&dwback);
memcpy(jmp,src,len);
jmp += len;
jmp[0] = 0xE9;
*(DWORD*)(jmp+1) = (DWORD)(src+len - jmp) - 5;
src[0] = 0xE9;
*(DWORD*)(src+1) = (DWORD)(dst - src) - 5;
VirtualProtect(src,len,dwback,&dwback);
return (jmp-len);
}
for it. These function detours the function src (f.e. MessageBoxA()) to function dst. As len you can use 5. It returns a function pointer to the original function.
An example call:
typedef int (WINAPI *__MessageBox)(
__in_opt HWND hWnd,
__in_opt LPCTSTR lpText,
__in_opt LPCTSTR lpCaption,
__in UINT uType
);
__MessageBox _MessageBox;
int cMessageBox(HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType)
{
//here you can change anything you want
return _MessageBox(hWnd,lpText,lpCaption,uType);
}
int main(void)
{
BYTE *hookfunc = (BYTE*)GetProcAddress(LoadLibrary("user32.dll"),"MessageBoxA");
_MessageBox = (__MessageBox)DetourFunc(hookfunc,(BYTE*)cMessageBox,5);
return 0;
}
That's an usermode hook. If you want to do this systemwide I would use a device driver. Here is a tutorial about this. http://www.codeproject.com/KB/system/driverdev.aspx
And if you are using VC++ compile in multibyte mode ;).
If you want to hook in an other process just google DLL-Injection ;).
I just found out that someone is calling - from a signal handler - a definitely not async-signal-safe function that I wrote.
So, now I'm curious: how to circumvent this situation from happening again? I'd like to be able to easily determine if my code is running in signal handler context (language is C, but wouldn't the solution apply to any language?):
int myfunc( void ) {
if( in_signal_handler_context() ) { return(-1) }
// rest of function goes here
return( 0 );
}
This is under Linux.
Hope this isn't an easy answer, or else I'll feel like an idiot.
Apparently, newer Linux/x86 (probably since some 2.6.x kernel) calls signal handlers from the vdso. You could use this fact to inflict the following horrible hack upon the unsuspecting world:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
uintmax_t vdso_start = 0;
uintmax_t vdso_end = 0; /* actually, next byte */
int check_stack_for_vdso(uint32_t *esp, size_t len)
{
size_t i;
for (i = 0; i < len; i++, esp++)
if (*esp >= vdso_start && *esp < vdso_end)
return 1;
return 0;
}
void handler(int signo)
{
uint32_t *esp;
__asm__ __volatile__ ("mov %%esp, %0" : "=r"(esp));
/* XXX only for demonstration, don't call printf from a signal handler */
printf("handler: check_stack_for_vdso() = %d\n", check_stack_for_vdso(esp, 20));
}
void parse_maps()
{
FILE *maps;
char buf[256];
char path[7];
uintmax_t start, end, offset, inode;
char r, w, x, p;
unsigned major, minor;
maps = fopen("/proc/self/maps", "rt");
if (maps == NULL)
return;
while (!feof(maps) && !ferror(maps)) {
if (fgets(buf, 256, maps) != NULL) {
if (sscanf(buf, "%jx-%jx %c%c%c%c %jx %u:%u %ju %6s",
&start, &end, &r, &w, &x, &p, &offset,
&major, &minor, &inode, path) == 11) {
if (!strcmp(path, "[vdso]")) {
vdso_start = start;
vdso_end = end;
break;
}
}
}
}
fclose(maps);
printf("[vdso] at %jx-%jx\n", vdso_start, vdso_end);
}
int main()
{
struct sigaction sa;
uint32_t *esp;
parse_maps();
memset(&sa, 0, sizeof(struct sigaction));
sa.sa_handler = handler;
sa.sa_flags = SA_RESTART;
if (sigaction(SIGUSR1, &sa, NULL) < 0) {
perror("sigaction");
exit(1);
}
__asm__ __volatile__ ("mov %%esp, %0" : "=r"(esp));
printf("before kill: check_stack_for_vdso() = %d\n", check_stack_for_vdso(esp, 20));
kill(getpid(), SIGUSR1);
__asm__ __volatile__ ("mov %%esp, %0" : "=r"(esp));
printf("after kill: check_stack_for_vdso() = %d\n", check_stack_for_vdso(esp, 20));
return 0;
}
SCNR.
If we can assume your application doesn't manually block signals using sigprocmask() or pthread_sigmask(), then this is pretty simple: get your current thread ID (tid). Open /proc/tid/status and get the values for SigBlk and SigCgt. AND those two values. If the result of that AND is non-zero, then that thread is currently running from inside a signal handler. I've tested this myself and it works.
There are two proper ways to deal with this:
Have your co-workers stop doing the wrong thing. Good luck pulling this off with the boss, though...
Make your function re-entrant and async-safe. If necessary, provide a function with a different signature (e.g. using the widely-used *_r naming convention) with the additional arguments that are necessary for state preservation.
As for the non-proper way to do this, on Linux with GNU libc you can use backtrace() and friends to go through the caller list of your function. It's not easy to get right, safe or portable, but it might do for a while:
/*
* *** Warning ***
*
* Black, fragile and unportable magic ahead
*
* Do not use this, lest the daemons of hell be unleashed upon you
*/
int in_signal_handler_context() {
int i, n;
void *bt[1000];
char **bts = NULL;
n = backtrace(bt, 1000);
bts = backtrace_symbols(bt, n);
for (i = 0; i < n; ++i)
printf("%i - %s\n", i, bts[i]);
/* Have a look at the caller chain */
for (i = 0; i < n; ++i) {
/* Far more checks are needed here to avoid misfires */
if (strstr(bts[i], "(__libc_start_main+") != NULL)
return 0;
if (strstr(bts[i], "libc.so.6(+") != NULL)
return 1;
}
return 0;
}
void unsafe() {
if (in_signal_handler_context())
printf("John, you know you are an idiot, right?\n");
}
In my opinion, it might just be better to quit rather than be forced to write code like this.
You could work out something using sigaltstack. Set up an alternative signal stack, get the stack pointer in some async-safe way, if within the alternative stack go on, otherwise abort().
I guess you need to do the following. This is a complex solution, which combines the best practices not only from coding, but from software engineering as well!
Persuade your boss that naming convention on signal handlers is a good thing. Propose, for example, a Hungarian notation, and tell that it was used in Microsoft with great success.
So, all signal handlers will start with sighnd, like sighndInterrupt.
Your function that detects signal handling context would do the following:
Get the backtrace().
Look if any of the functions in it begin with sighnd.... If it does, then congratulations, you're inside a signal handler!
Otherwise, you're not.
Try to avoid working with Jimmy in the same company. "There can be only one", you know.
for code optimized at -O2 or better (istr) have found need to add -fno-omit-frame-pointer
else gcc will optimize out the stack context information