Add signal safety test suite (#365)

* Add signal safety test suite

* Remove binary file from repository

---------

Co-authored-by: Levi Neely <lkn@darkstar.example.net>

tests/test_signal_safety.c

@@ -0,0 +1,112 @@
+/*
+ * Test: Signal safety with pthread_mutex_timedlock (pcl-17t)
+ *
+ * Verifies that signal handlers do not deadlock when signals are raised
+ * while holding mutexes, using the timeout mechanism from pthread_mutex_timedlock.
+ */
+
+#define _DEFAULT_SOURCE
+#define _POSIX_C_SOURCE 200809L
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <signal.h>
+#include <time.h>
+#include <errno.h>
+#include <unistd.h>
+
+static pthread_mutex_t test_mutex = PTHREAD_MUTEX_INITIALIZER;
+static volatile sig_atomic_t signal_received = 0;
+static volatile sig_atomic_t handler_attempted_lock = 0;
+static volatile sig_atomic_t handler_timeout = 0;
+
+static void signal_handler(int sig) {
+    (void)sig;
+    signal_received = 1;
+    handler_attempted_lock = 1;
+    
+    struct timespec ts;
+    clock_gettime(CLOCK_REALTIME, &ts);
+    ts.tv_sec += 1;
+    
+    int ret = pthread_mutex_timedlock(&test_mutex, &ts);
+    if (ret == ETIMEDOUT) {
+        handler_timeout = 1;
+    } else if (ret == 0) {
+        pthread_mutex_unlock(&test_mutex);
+    }
+}
+
+static int passes = 0, failures = 0;
+#define PASS(n)      do { printf("PASS: %s\n", n); passes++; } while(0)
+#define FAIL(n, ...) do { printf("FAIL: %s — ", n); printf(__VA_ARGS__); printf("\n"); failures++; } while(0)
+
+static void test_signal_while_holding_lock(void) {
+    signal_received = 0;
+    handler_attempted_lock = 0;
+    handler_timeout = 0;
+    
+    struct sigaction sa = {0};
+    sa.sa_handler = signal_handler;
+    sigaction(SIGUSR1, &sa, NULL);
+    
+    pthread_mutex_lock(&test_mutex);
+    raise(SIGUSR1);
+    usleep(10000);
+    pthread_mutex_unlock(&test_mutex);
+    
+    if (signal_received && handler_attempted_lock && handler_timeout)
+        PASS("signal raised while holding lock: handler timeout, no deadlock");
+    else
+        FAIL("signal while holding lock", "received=%d attempted=%d timeout=%d",
+             signal_received, handler_attempted_lock, handler_timeout);
+}
+
+static void test_signal_handler_acquires_lock(void) {
+    signal_received = 0;
+    handler_attempted_lock = 0;
+    handler_timeout = 0;
+    
+    struct sigaction sa = {0};
+    sa.sa_handler = signal_handler;
+    sigaction(SIGUSR1, &sa, NULL);
+    
+    raise(SIGUSR1);
+    usleep(10000);
+    
+    if (signal_received && handler_attempted_lock && !handler_timeout)
+        PASS("signal handler acquires lock when available");
+    else
+        FAIL("signal handler acquires lock", "received=%d attempted=%d timeout=%d",
+             signal_received, handler_attempted_lock, handler_timeout);
+}
+
+static void test_no_deadlock_with_timeout(void) {
+    signal_received = 0;
+    handler_attempted_lock = 0;
+    handler_timeout = 0;
+    
+    struct sigaction sa = {0};
+    sa.sa_handler = signal_handler;
+    sigaction(SIGUSR1, &sa, NULL);
+    
+    pthread_mutex_lock(&test_mutex);
+    raise(SIGUSR1);
+    usleep(1500000);
+    pthread_mutex_unlock(&test_mutex);
+    
+    if (signal_received && handler_timeout)
+        PASS("no deadlock: timeout mechanism prevents hang");
+    else
+        FAIL("no deadlock with timeout", "received=%d timeout=%d",
+             signal_received, handler_timeout);
+}
+
+int main(void) {
+    test_signal_while_holding_lock();
+    test_signal_handler_acquires_lock();
+    test_no_deadlock_with_timeout();
+    
+    printf("\n%d passed, %d failed\n", passes, failures);
+    return failures ? 1 : 0;
+}