* Steve McClure, 1998
*/
+/*
+ * This header defines Empire's abstract thread interface. There are
+ * several concrete implementations.
+ *
+ * Empire threads are non-preemptive, i.e. they run until they
+ * voluntarily yield the processor. The thread scheduler then picks
+ * one of the runnable threads with the highest priority. Priorities
+ * are static. Empire code relies on these properties heavily. The
+ * most common form of yielding the processor is sleeping for some
+ * event to happen.
+ */
+
#ifndef _EMTHREAD_H_
#define _EMTHREAD_H_
#ifdef _EMPTH_LWP
#include "lwp.h"
+
+/* Abstract data types */
+
+/* empth_t * represents a thread. */
typedef struct lwpProc empth_t;
+
+/* empth_sem_t * represents a semaphore */
typedef struct lwpSem empth_sem_t;
+
+/* Flags for empth_select(): whether to sleep on input or output */
#define EMPTH_FD_READ LWP_FD_READ
#define EMPTH_FD_WRITE LWP_FD_WRITE
+
+/* Flags for empth_init() and empth_create() */
+/* Request debug prints */
#define EMPTH_PRINT LWP_PRINT
+/* Request stack checking */
#define EMPTH_STACKCHECK LWP_STACKCHECK
-#endif
+
+#endif /* _EMPTH_LWP */
#ifdef _EMPTH_POSIX
#ifdef __linux__
pthread_cond_t cnd_sem;
} empth_sem_t;
-#endif
+#endif /* _EMPTH_POSIX */
/* DEC has slightly different names for whatever reason... */
#ifdef _DECTHREADS_
typedef struct loc_Sem_t empth_sem_t;
void empth_request_shutdown(void);
-#endif
+#endif /* _EMPTH_WIN32 */
-int empth_init(char **ctx, int flags);
-empth_t *empth_create(int, void (*)(void *), int, int, char *, char *, void *);
+/*
+ * Initialize thread package.
+ * CTX points to a thread context variable; see empth_create().
+ * FLAGS request optional features.
+ * Should return 0 on success, -1 on error, but currently always
+ * returns 0.
+ */
+int empth_init(void **ctx, int flags);
+
+/*
+ * Create a new thread.
+ * PRIO is the scheduling priority.
+ * ENTRY is the entry point. It will be called with argument UD.
+ * Thread stack is at least SIZE bytes.
+ * FLAGS should be the same as were passed to empth_init(), or zero.
+ * NAME is the threads name, and DESC its description. These are used
+ * for logging and debugging.
+ * UD is the value to pass to ENTRY. It is also assigned to the
+ * context variable defined with empth_init() whenever the thread gets
+ * scheduled.
+ * Return the thread, or NULL on error.
+ */
+empth_t *empth_create(int prio, void (*entry)(void *),
+ int size, int flags, char *name, char *desc, void *ud);
+
+/*
+ * Return the current thread.
+ */
empth_t *empth_self(void);
+
+/*
+ * Terminate the current thread.
+ * Never returns.
+ */
void empth_exit(void);
+
+/*
+ * Yield the processor.
+ */
void empth_yield(void);
-void empth_terminate(empth_t *);
+
+/*
+ * Terminate THREAD.
+ * THREAD will not be scheduled again. Instead, it will terminate as
+ * if it executed empth_exit(). It is unspecified when exactly that
+ * happens.
+ * THREAD must not be the current thread.
+ */
+void empth_terminate(empth_t *thread);
+
+/*
+ * Put current thread to sleep until file descriptor FD is ready for I/O.
+ * If FLAGS & EMPTH_FD_READ, wake up if FD is ready for input.
+ * If FLAGS & EMPTH_FD_WRITE, wake up if FD is ready for output.
+ * Note: Currently, Empire sleeps only on network I/O, i.e. FD is a
+ * socket. Implementations should not rely on that.
+ */
void empth_select(int fd, int flags);
-void empth_wakeup(empth_t *);
-void empth_sleep(long until);
+
+/*
+ * Awaken THREAD if it is sleeping in empth_select().
+ * Note: This must not awaken threads sleeping in other functions.
+ */
+void empth_wakeup(empth_t *thread);
+
+/*
+ * Put current thread to sleep until the time is UNTIL.
+ * May sleep somehwat longer, but never shorter.
+ */
+void empth_sleep(time_t until);
+
+/*
+ * Create a semaphore.
+ * NAME is its name, it is used for debugging.
+ * COUNT is the initial count value of the semaphore, it must not be
+ * negative.
+ * Return the semaphore, or NULL on error.
+ */
empth_sem_t *empth_sem_create(char *name, int count);
-void empth_sem_signal(empth_sem_t *);
-void empth_sem_wait(empth_sem_t *);
+
+/*
+ * Signal SEM.
+ * Increase SEM's count. If threads are sleeping on it, wake up
+ * exactly one of them. If that thread has a higher priority, yield
+ * the processor.
+ * This semaphore operation is often called `down' or `V' otherwhere.
+ */
+void empth_sem_signal(empth_sem_t *sem);
+
+/*
+ * Wait for SEM.
+ * If SEM has a zero count, put current thread to sleep until
+ * empth_sem_signal() awakens it. SEM will have non-zero value then.
+ * Decrement SEM's count.
+ * This semaphore operation is often called `up' or `P' otherwhere.
+ */
+void empth_sem_wait(empth_sem_t *sem);
+
+/* Internal function, not part of the thread abstraction */
void empth_alarm(int);
#endif