[BUGFIX] Fix thpool_destroy() hang: unlock all workers at once

tests/src/thpool_destroy_hang.c

@@ -0,0 +1,55 @@
+/*
+ * Reproduces the “hang inside thpool_destroy()” bug.
+ *   – Fails (SIGALRM) with the original binary-semaphore implementation.
+ *   – Succeeds instantly once bsem_wait / bsem_post_all are patched.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <sys/time.h>
+#include "../../thpool.h"
+
+#define TIMEOUT 1
+
+/* -------------------------------------------------------------- */
+/* 2. SIGALRM handler: triggers when thpool_destroy() does not    */
+/*    return within 1 sec, indicating the bug is reproduced.      */
+/* -------------------------------------------------------------- */
+static void timeout_handler(int sig)
+{
+    (void)sig;
+    fprintf(stderr,
+            "FAIL: thpool_destroy() did not finish within %d s "
+            "(bug reproduced)\n", TIMEOUT);
+    _exit(EXIT_FAILURE);
+}
+
+int main(void)
+{
+    const int THREADS = 4000;
+
+    /* Watchdog: if we are still alive after 3 s, the bug is present */
+    signal(SIGALRM, timeout_handler);
+    alarm(TIMEOUT);
+
+    printf("Creating pool with %d threads …\n", THREADS);
+    threadpool tp = thpool_init(THREADS);
+
+    struct timeval t0, t1;
+    gettimeofday(&t0, NULL);
+
+    printf("Calling thpool_destroy() …\n");
+    thpool_destroy(tp);      /* ← hangs here when not patched */
+
+    gettimeofday(&t1, NULL);
+    alarm(0); /* disarm watchdog */
+
+    double elapsed =
+        (t1.tv_sec - t0.tv_sec) + (t1.tv_usec - t0.tv_usec) / 1e6;
+
+    printf("PASS: thpool_destroy() returned in %.3f s (patch OK)\n",
+           elapsed);
+    return 0;
+}

tests/thpool_destroy_hang.sh

@@ -0,0 +1,25 @@
+#! /bin/bash
+#
+# Test for the deterministic thpool_destroy() hang
+#
+
+. funcs.sh
+
+# -------------------------------------------------- #
+# Single test: must finish without hitting SIGALRM   #
+# -------------------------------------------------- #
+function test_thpool_destroy_hang {
+    compile src/thpool_destroy_hang.c
+    echo "Testing for thpool_destroy() hang"
+    output=$(timeout 2 ./test)
+    if [[ $? != 0 ]]; then
+        err "thpool_destroy() hang reproduced" "$output"
+        exit 1
+    fi
+
+}
+
+# Run the test
+test_thpool_destroy_hang
+
+echo "No errors"

thpool.c

@@ -25,6 +25,7 @@
 #include <pthread.h>
 #include <errno.h>
 #include <time.h>
+#include <limits.h>
 #if defined(__linux__)
 #include <sys/prctl.h>
 #endif
@@ -554,7 +555,7 @@ static void bsem_post(bsem *bsem_p) {
 /* Post to all threads */
 static void bsem_post_all(bsem *bsem_p) {
 	pthread_mutex_lock(&bsem_p->mutex);
-	bsem_p->v = 1;
+	bsem_p->v = INT_MAX;
 	pthread_cond_broadcast(&bsem_p->cond);
 	pthread_mutex_unlock(&bsem_p->mutex);
 }
@@ -563,9 +564,9 @@ static void bsem_post_all(bsem *bsem_p) {
 /* Wait on semaphore until semaphore has value 0 */
 static void bsem_wait(bsem* bsem_p) {
 	pthread_mutex_lock(&bsem_p->mutex);
-	while (bsem_p->v != 1) {
+	while (bsem_p->v == 0) {
 		pthread_cond_wait(&bsem_p->cond, &bsem_p->mutex);
 	}
-	bsem_p->v = 0;
+	bsem_p->v--;
 	pthread_mutex_unlock(&bsem_p->mutex);
 }