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.gitignore

+/* pthread lock */
+#include <stdlib.h>
+#include <pthread.h>
+
+#define NHASH 29
+#define HASH(id) (((unsigned long)id)%NHASH)
+
+struct foo *fh[NHASH];
+pthread_mutex_t hashlock = PTHREAD_MUTEX_INITIALIZER;
+
+struct foo {
+	int             f_count; /* protected by hashlock */
+	pthread_mutex_t f_lock;
+	int             f_id;
+	struct foo     *f_next; /* protected by hashlock */
+	/* ... more stuff here ... */
+};
+
+struct foo *
+foo_alloc(int id) /* allocate the object */
+{
+	struct foo	*fp;
+	int			idx;
+
+	if ((fp = malloc(sizeof(struct foo))) != NULL) {
+		fp->f_count = 1;
+		fp->f_id = id;
+		if (pthread_mutex_init(&fp->f_lock, NULL) != 0) {
+			free(fp);
+			return(NULL);
+		}
+		idx = HASH(id);
+		pthread_mutex_lock(&hashlock);
+		fp->f_next = fh[idx];
+		fh[idx] = fp;
+		pthread_mutex_lock(&fp->f_lock);
+		pthread_mutex_unlock(&hashlock);
+		/* ... continue initialization ... */
+		pthread_mutex_unlock(&fp->f_lock);
+	}
+	return(fp);
+}
+
+void
+foo_hold(struct foo *fp) /* add a reference to the object */
+{
+	pthread_mutex_lock(&hashlock);
+	fp->f_count++;
+	pthread_mutex_unlock(&hashlock);
+}
+
+struct foo *
+foo_find(int id) /* find an existing object */
+{
+	struct foo	*fp;
+
+	pthread_mutex_lock(&hashlock);
+	for (fp = fh[HASH(id)]; fp != NULL; fp = fp->f_next) {
+		if (fp->f_id == id) {
+			fp->f_count++;
+			break;
+		}
+	}
+	pthread_mutex_unlock(&hashlock);
+	return(fp);
+}
+
+void
+foo_rele(struct foo *fp) /* release a reference to the object */
+{
+	struct foo	*tfp;
+	int			idx;
+
+	pthread_mutex_lock(&hashlock);
+	if (--fp->f_count == 0) { /* last reference, remove from list */
+		idx = HASH(fp->f_id);
+		tfp = fh[idx];
+		if (tfp == fp) {
+			fh[idx] = fp->f_next;
+		} else {
+			while (tfp->f_next != fp)
+				tfp = tfp->f_next;
+			tfp->f_next = fp->f_next;
+		}
+		pthread_mutex_unlock(&hashlock);
+		pthread_mutex_destroy(&fp->f_lock);
+		free(fp);
+	} else {
+		pthread_mutex_unlock(&hashlock);
+	}
+}
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