pbio/os: Add way to request cancellation.

This will eventually replace task->cancel as well as PROCESS_EXITHANDLER.

Author: laurensvalk

lib/pbio/include/pbio/os.h

@@ -83,6 +83,24 @@ typedef pbio_error_t (*pbio_os_process_func_t)(pbio_os_state_t *state, void *con
 
 typedef struct _pbio_os_process_t pbio_os_process_t;
 
+/**
+ * Requests that can be made to a process.
+ *
+ * The event loop will not enforce any particular response. It is up to the
+ * thread to handle (or ignore) the request and exit with some return code when
+ * it sees fit, not necessarily immediately.
+ */
+typedef enum {
+    /**
+     * No requests.
+     */
+    PBIO_OS_PROCESS_REQUEST_TYPE_NONE = 0,
+    /**
+     * Ask the process to cancel/exit.
+     */
+    PBIO_OS_PROCESS_REQUEST_TYPE_CANCEL = 1 << 1,
+} pbio_os_process_request_type_t;
+
 /**
  * A process.
  */
@@ -107,6 +125,11 @@ struct _pbio_os_process_t {
      * Most recent result of running one iteration of the protothread.
      */
     pbio_error_t err;
+    /**
+     * Request made to the process such as cancellation. It is up to the
+     * thread function to implement how to respond, if at all.
+     */
+    pbio_os_process_request_type_t request;
 };
 
 /**

lib/pbio/src/os.c

@@ -49,7 +49,7 @@ void pbio_os_request_poll(void) {
 static pbio_os_process_t *process_list = NULL;
 
 /**
- * Placeholder thread that does nothing.
+ * Placeholder thread that does nothing and never completes.
  *
  * @param [in] state The protothread state.
  * @param [in] context The context.
@@ -98,6 +98,7 @@ void pbio_os_process_start(pbio_os_process_t *process, pbio_os_process_func_t fu
 void pbio_os_process_init(pbio_os_process_t *process, pbio_os_process_func_t func) {
     process->err = PBIO_ERROR_AGAIN;
     process->state = 0;
+    process->request = PBIO_OS_PROCESS_REQUEST_TYPE_NONE;
     if (func) {
         process->func = func;
     }
@@ -106,6 +107,20 @@ void pbio_os_process_init(pbio_os_process_t *process, pbio_os_process_func_t fun
     pbio_os_request_poll();
 }
 
+/**
+ * Makes a request to a process.
+ *
+ * It is like sending a signal to the process. It is up to the process to
+ * respond or ignore it.
+ *
+ * @param process   The process.
+ * @param request   The request to make.
+ */
+void pbio_os_process_make_request(pbio_os_process_t *process, pbio_os_process_request_type_t request) {
+    process->request = request;
+    pbio_os_request_poll();
+}
+
 /**
  * Drives the event loop once: Runs one iteration of all processes.
  *