libcilkrts/runtime/local_state.h

/* local_state.h                  -*-C++-*-
 *
 *************************************************************************
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/**
 * @file local_state.h
 *
 * @brief The local_state structure contains additional OS-independent
 * information that's associated with a worker, but doesn't need to be visible
 * to the code generated by the compiler.
 */

#ifndef INCLUDED_LOCAL_STATE_DOT_H
#define INCLUDED_LOCAL_STATE_DOT_H

#include <internal/abi.h>
#include "worker_mutex.h"
#include "global_state.h"
#include "record-replay.h"
#include "signal_node.h"

#include <setjmp.h>
#include <stddef.h>
#include <stdio.h>


#ifndef _WIN32
#   include <pthread.h>
#endif

__CILKRTS_BEGIN_EXTERN_C

/* Opaque types. */

struct full_frame;
struct free_list;
struct pending_exception_info;
/// Opaque type for replay entry. 
typedef struct replay_entry_t replay_entry_t;

/**
 * @brief Magic numbers for local_state, used for debugging
 */
typedef unsigned long long ls_magic_t;

/**
 * @brief Scheduling stack function: A function that is decided on the program stack,
 * but that must be executed on the scheduling stack.
 */
typedef void (*scheduling_stack_fcn_t) (__cilkrts_worker *w,
                                        struct full_frame *ff,
                                        __cilkrts_stack_frame *sf);

/**
 * @brief Type of this worker.
 **/
typedef enum cilk_worker_type
{
    WORKER_FREE,    ///< Unused worker - available to be bound to user threads
    WORKER_SYSTEM,  ///< Worker created by runtime - able to steal from any worker
    WORKER_USER     ///< User thread - able to steal only from team members
} cilk_worker_type;


/**
 * @brief The local_state structure contains additional OS-independent
 * information that's associated with a worker, but doesn't need to be
 * visible to the compiler.
 *
 * No compiler-generated code should need to know the layout of this
 * structure.
 *
 * The fields of this struct can be classified as either local or
 * shared.
 *
 *  Local: This field is only accessed by the thread bound to this
 *    worker struct.  Local fields can be freely accessed without
 *    acquiring locks.
 *  
 *  Shared: This field may be accessed by multiple worker threads.
 *    Accesses to shared fields usually requires locks, except in
 *    special situations where one can prove that locks are
 *    unnecessary.
 *
 * The fields of this can also be classified as "read-only" if the
 * field does not change after it is initialized.  Otherwise, the
 * field is "read/write".  Read-only fields do not require locks to
 * access (ignoring the synchronization that might be needed for
 * initialization if this can occur in parallel).
 *
 * Finally, we explicitly classify some fields as "synchronization"
 * fields if they are used as part of a synchronization protocol in
 * the runtime.  These variables are generally shared and read/write.
 * Mostly, this category includes lock variables and other variables
 * that are involved in synchronization protocols (i.e., the THE
 * protocol).
 */
struct local_state  /* COMMON_PORTABLE */
{
    /** This value should be in the first field in any local_state */
#   define WORKER_MAGIC_0 ((ls_magic_t)0xe0831a4a940c60b8ULL)

    /**
     * Should be WORKER_MAGIC_0 or the local_state has been corrupted
     * This magic field is shared because it is read on lock acquisitions.
     *
     * [shared read-only]
     */
    ls_magic_t worker_magic_0;

    /**
     * Mutex used to serialize access to the local_state
     * Synchronization field. [shared read/write]
     */
    struct mutex lock;

    /**
     * Flag that indicates that the worker is interested in grabbing
     * LOCK, and thus thieves should leave the worker alone.
     * Written only by self, may be read by others.
     *
     * Synchronization field.  [shared read/write]
     */
    int do_not_steal;

    /**
     * Lock that all thieves grab in order to compete for the right
     * to disturb this worker.
     *
     * Synchronization field. [shared read/write]
     */
    struct mutex steal_lock;

    /**
     * Full frame that the worker is working on.
     *
     * While a worker w is executing, a thief may change
     * w->l->frame_ff (on a successful steal) after acquiring w's
     * lock.
     *
     * Unlocked accesses to w->l->frame_ff are safe (by w itself) when
     * w's deque is empty, or when stealing from w has been disabled.
     *
     * [shared read/write]
     */
    struct full_frame *frame_ff;

    /**
     * Full frame that the worker will be working on next
     *
     * This field is normally local for a worker w.  Another worker v
     * may modify w->l->next_frame_ff, however, in the special case
     * when v is returning a frame to a user thread w since w is the
     * team leader.
     *
     * [shared read/write]
     */
    struct full_frame *next_frame_ff;

    /**
     * This is set iff this is a WORKER_USER and there has been a steal.  It
     * points to the first frame that was stolen since the team was last fully
     * sync'd.  Only this worker may continue past a sync in this function.
     *
     * This field is set by a thief for a victim that is a user
     * thread, while holding the victim's lock.
     * It can be cleared without a lock by the worker that will
     * continue exuecting past the sync.
     *
     * [shared read/write]
     */
    struct full_frame *last_full_frame;

    /**
     * Team on which this worker is a participant.  When a user worker enters,
     * its team is its own worker struct and it can never change teams.  When a
     * system worker steals, it adopts the team of its victim.
     *
     * When a system worker w steals, it reads victim->l->team and
     * joins this team.  w->l->team is constant until the next time w
     * returns control to the runtime.
     * We must acquire the worker lock to change w->l->team.
     *
     * @note This field is 64-byte aligned because it is the first in
     * the group of shared read-only fields.  We want this group to
     * fall on a different cache line from the previous group, which
     * is shared read-write.
     *
     * [shared read-only]
     */
    __attribute__((aligned(64)))
    __cilkrts_worker *team;

    /**
     * Type of this worker
     *
     * This field changes only when a worker binds or unbinds.
     * Otherwise, the field is read-only while the worker is bound.
     *
     * [shared read-only]
     */
    cilk_worker_type type;
    
    /**
     * Lazy task queue of this worker - an array of pointers to stack frames.
     *
     * Read-only because deques are a fixed size in the current
     * implementation.
     *
     * @note This field is 64-byte aligned because it is the first in
     * the group of local fields.  We want this group to fall on a
     * different cache line from the previous group, which is shared
     * read-only.
     *
     * [local read-only]
     */
    __attribute__((aligned(64)))
    __cilkrts_stack_frame **ltq;

    /**
     * Pool of fibers waiting to be reused.
     * [local read/write]
     */
    cilk_fiber_pool fiber_pool;

    /**
     * The fiber for the scheduling stacks.
     * [local read/write]
     */
    cilk_fiber* scheduling_fiber;

    /**
     * Saved pointer to the leaf node in thread-local storage, when a
     * user thread is imported.  This pointer gets set to a
     * meaningful value when binding a user thread, and cleared on
     * unbind.
     *
     * [local read/write]
     */
    __cilkrts_pedigree* original_pedigree_leaf;

    /**
     * State of the random number generator
     * 
     * [local read/write]
     */
    unsigned rand_seed;

    /**
     * Function to execute after transferring onto the scheduling stack.
     *
     * [local read/write]
     */
    scheduling_stack_fcn_t post_suspend;

    /**
     * __cilkrts_stack_frame we suspended when we transferred onto the
     * scheduling stack.    
     *
     * [local read/write]
     */
    __cilkrts_stack_frame *suspended_stack;

    /**
     * cilk_fiber that should be freed after returning from a
     *  spawn with a stolen parent or after stalling at a sync.

     *  We calculate the stack to free when executing a reduction on
     *  the user stack, but we can not actually release the stack
     *  until control longjmps onto a runtime scheduling stack.
     *
     * This field is used to pass information to the runtime across
     * the longjmp onto the scheduling stack.
     *
     * [local read/write]
     */
    cilk_fiber* fiber_to_free;

    /**
     * Saved exception object for an exception that is being passed to
     * our parent
     *
     * [local read/write]
     */
    struct pending_exception_info *pending_exception;

    /**
     * Buckets for the memory allocator
     *
     * [local read/write]
     */
    struct free_list *free_list[FRAME_MALLOC_NBUCKETS];

    /**
     * Potential function for the memory allocator
     *
     * [local read/write]
     */
    size_t bucket_potential[FRAME_MALLOC_NBUCKETS];

    /**
     * Support for statistics
     *
     * Useful only when CILK_PROFIlE is compiled in. 
     * [local read/write]
     */
    statistics* stats;

    /**
     * Count indicates number of failures since last successful steal.  This is
     * used by the scheduler to reduce contention on shared flags.
     *
     * [local read/write]
     */
    unsigned int steal_failure_count;

    /**
     * Record indicating that the worker stole work at least once.
     *
     * [local read/write]
     */
    int has_stolen;

    /**
     * 1 if work was stolen from another worker.  When true, this will flag
     * setup_for_execution_pedigree to increment the pedigree when we resume
     * execution to match the increment that would have been done on a return
     * from a spawn helper.
     *
     * [local read/write]
     */
    int work_stolen;

    /**
     * File pointer for record or replay
     * Does FILE * work on Windows?
     * During record, the file will be opened in write-only mode.
     * During replay, the file will be opened in read-only mode.
     *
     * [local read/write]
     */
    FILE *record_replay_fptr;

    /**
     * Root of array of replay entries - NULL if we're not replaying a log
     *
     * [local read/write]
     */
    replay_entry_t *replay_list_root;

    /**
     * Current replay entry - NULL if we're not replaying a log
     *
     * [local read/write]
     */
    replay_entry_t *replay_list_entry;
    
    /**
     * Separate the signal_node from other things in the local_state by the
     * sizeof a cache line for performance reasons.
     *
     * unused 
     */
    char buf[64];

    /**
     * Signal object for waking/sleeping the worker.  This should be a pointer
     * to avoid the possibility of caching problems.
     *
     * [shared read-only]
     */
     signal_node_t *signal_node;

    /** This value should be in the last field in any local_state */
#   define WORKER_MAGIC_1 ((ls_magic_t)0x16164afb0ea0dff9ULL)

    /**
     * Should be WORKER_MAGIC_1 or the local_state has been corrupted
     * This magic field is shared because it is read on lock acquisitions.
     * [shared read-only]
     */
    ls_magic_t worker_magic_1;
};

/**
 * Perform cleanup according to the function set before the longjmp().
 *
 * Call this after longjmp() has completed and the worker is back on a
 * scheduling stack.
 *
 * @param w __cilkrts_worker currently executing.
 */
void run_scheduling_stack_fcn(__cilkrts_worker *w);

__CILKRTS_END_EXTERN_C

#endif // ! defined(INCLUDED_LOCAL_STATE_DOT_H)