core: add simple mailbox library

A very simple mailbox library, designed for lwIP porting.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

2 files changed, 88 insertions, 0 deletions

diff --git a/core/include/mbox.h b/core/include/mbox.h
new file mode 100644
index 00000000..ac139ff5
--- /dev/null
+++ b/core/include/mbox.h
@@ -0,0 +1,24 @@
+/*
+ * mbox.h
+ *
+ * Simple thread mailbox interface
+ */
+
+#ifndef _MBOX_H
+#define _MBOX_H
+
+#include "thread.h"
+
+struct mailbox {
+    struct semaphore prod_sem;	/* Producer semaphore (empty slots) */
+    struct semaphore cons_sem;	/* Consumer semaphore (data slots) */
+    struct semaphore head_sem;	/* Head pointer semaphore */
+    struct semaphore tail_sem;	/* Tail pointer semaphore */
+    void **wrap;		/* Where pointers wrap */
+    void **head;		/* Head pointer */
+    void **tail;		/* Tail pointer */
+
+    void *data[];		/* Data array */
+};
+
+#endif /* _MBOX_H */
diff --git a/core/thread/mbox.c b/core/thread/mbox.c
new file mode 100644
index 00000000..107b51bf
--- /dev/null
+++ b/core/thread/mbox.c
@@ -0,0 +1,64 @@
+/*
+ * mbox.c
+ *
+ * Simple thread mailbox interface
+ */
+
+#include "thread.h"
+#include "mbox.h"
+#include <errno.h>
+
+void mbox_init(struct mailbox *mbox, size_t size)
+{
+    sem_init(&mbox->prod_sem, size); /* All slots empty */
+    sem_init(&mbox->cons_sem, 0);    /* No slots full */
+    sem_init(&mbox->head_sem, 1);    /* Head mutex */
+    sem_init(&mbox->tail_sem, 1);    /* Tail mutex */
+
+    mbox->wrap = &mbox->data[size];
+    mbox->head = &mbox->data[0];
+    mbox->tail = &mbox->data[0];
+};
+
+static void mbox_post_common(struct mailbox *mbox, void *msg)
+{
+    sem_down(&mbox->head_sem, 0);
+
+    *mbox->head = msg;
+    mbox->head++;
+    if (mbox->head == mbox->wrap)
+	mbox->head = &mbox->data[0];
+
+    sem_up(&mbox->head_sem);
+    sem_up(&mbox->cons_sem);
+}
+
+void mbox_post(struct mailbox *mbox, void *msg)
+{
+    sem_down(&mbox->prod_sem, 0);
+    mbox_post_common(mbox, msg);
+}
+
+int mbox_trypost(struct mailbox *mbox, void *msg)
+{
+    if (sem_down(&mbox->prod_sem, -1) == (jiffies_t)-1)
+	return ENOMEM;
+    mbox_post_common(mbox, msg);
+    return 0;
+}
+
+jiffies_t mbox_fetch(struct mailbox *mbox, void **msg, jiffies_t timeout)
+{
+    if (sem_down(&mbox->cons_sem, timeout) == (jiffies_t)-1)
+	return -1;
+    sem_down(&mbox->tail_sem, 0);
+
+    if (msg)
+	*msg = *mbox->tail;
+    mbox->tail++;
+    if (mbox->tail == mbox->wrap)
+	mbox->tail = &mbox->data[0];
+
+    sem_up(&mbox->tail_sem);
+    sem_up(&mbox->prod_sem);
+}