Reinstall signal handler when Python signal handler called

src/cysignals/implementation.c

@@ -681,7 +681,14 @@ static void setup_cysignals_handlers(void)
     sigprocmask(SIG_SETMASK, &default_sigmask, &sigmask_with_sigint);
 #endif
 
-    /* Install signal handlers */
+    /* Install signal handlers. We need a separate C-level interrupt handler
+     * apart from the Python-level interrupt handler because Python-level
+     * interrupt handler will not be called inside Cython code.
+     * See init_cysignals and python_check_interrupt for an explanation.
+     * A downside is the C-level interrupt handler will be overwritten
+     * when signal(SIGINT, getsignal(SIGINT)) is executed, in that case
+     * init_cysignals() need to be called again.
+     */
     /* Handlers for interrupt-like signals */
     sa.sa_handler = cysigs_interrupt_handler;
     sa.sa_flags = 0;

src/cysignals/signals.pxd

@@ -26,6 +26,7 @@ cdef extern from "struct_signals.h":
 
     ctypedef struct cysigs_t:
         cy_atomic_int sig_on_count
+        cy_atomic_int interrupt_received
         cy_atomic_int block_sigint
         const char* s
         PyObject* exc_value

src/cysignals/signals.pyx

@@ -353,6 +353,12 @@ def python_check_interrupt(sig, frame):
     ``implementation.c``.
     """
     sig_check()
+    # If this line is reached, a possibility is that something called
+    # signal(SIGINT, getsignal(SIGINT)), which cause cysigs_interrupt_handler
+    # to not be called. We reinstall the C-level signal handler.
+    init_cysignals()
+    cysigs.interrupt_received = sig
+    sig_check()
 
 
 cdef void verify_exc_value() noexcept:

src/cysignals/tests.pyx

@@ -35,6 +35,7 @@ from libc.errno cimport errno
 from posix.signal cimport sigaltstack, stack_t, SS_ONSTACK
 
 from cpython cimport PyErr_SetString
+from cpython.exc cimport PyErr_CheckSignals
 
 from .signals cimport *
 from .memory cimport *
@@ -805,6 +806,13 @@ def test_interrupt_bomb(long n=100, long p=10):
     i = 0
     while True:
         try:
+            # For some reason, without the line below, the exception
+            # will be detected too late (outside the try/except block)
+            # and the KeyboardInterrupt will be leaked outside,
+            # making the test fail.
+            # We can't really call PyErr_CheckSignals() from inside
+            # sig_on() because it does not hold the GIL.
+            PyErr_CheckSignals()
             with nogil:
                 sig_on()
                 ms_sleep(1000)
@@ -1124,7 +1132,7 @@ def test_sig_block_outside_sig_on(long delay=DEFAULT_DELAY):
         sig_unblock()
 
     try:
-        sig_on()  # Interrupt caught here
+        PyErr_CheckSignals()  # Interrupt caught here
     except KeyboardInterrupt:
         return "Success"
     abort()   # This should not be reached