Add an internal interface that allows the code to take advantage of multiple

cores by pushing subcomputations off into separate threads.  The interface
is not currently used.

FossilOrigin-Name: 0e4d977a4a07d6de50acbf022c7dd947998b8d96

src/threads.c

@@ -0,0 +1,120 @@
+/*
+** 2012 July 21
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+******************************************************************************
+**
+** This file presents a simple cross-platform threading interface for
+** use internally by SQLite.
+**
+** A "thread" can be created using sqlite3ThreadCreate().  This thread
+** runs independently of its creator until it is joined using
+** sqlite3ThreadJoin(), at which point it terminates.
+**
+** Threads do not have to be real.  It could be that the work of the
+** "thread" is done by the main thread at either the sqlite3ThreadCreate()
+** or sqlite3ThreadJoin() call.  This is, in fact, what happens in
+** single threaded systems.  Nothing in SQLite requires multiple threads.
+** This interface exists so that applications that want to take advantage
+** of multiple cores can do so, while also allowing applications to stay
+** single-threaded if desired.
+*/
+#include "sqliteInt.h"
+
+/********************************* Unix Pthreads ****************************/
+#if SQLITE_OS_UNIX && defined(SQLITE_MUTEX_PTHREADS)
+
+#define SQLITE_THREADS_IMPLEMENTED 1  /* Prevent the single-thread code below */
+#include <pthread.h>
+
+/* A running thread */
+struct SQLiteThread {
+  pthread_t tid;
+};
+
+/* Create a new thread */
+int sqlite3ThreadCreate(
+  SQLiteThread **ppThread,  /* OUT: Write the thread object here */
+  void *(*xTask)(void*),    /* Routine to run in a separate thread */
+  void *pIn                 /* Argument passed into xTask() */
+){
+  SQLiteThread *p;
+  int rc;
+
+  *ppThread = p = sqlite3Malloc(sizeof(*p));
+  if( p==0 ) return SQLITE_OK;
+  rc = pthread_create(&p->tid, 0, xTask, pIn);
+  if( rc ){
+    sqlite3_free(p);
+    return SQLITE_ERROR;
+  }
+  return SQLITE_OK;
+}
+
+/* Get the results of the thread */
+int sqlite3ThreadJoin(SQLiteThread *p, void **ppOut){
+  int rc;
+  if( p==0 ) return SQLITE_NOMEM;
+  rc = pthread_join(p->tid, ppOut);
+  sqlite3_free(p);
+  return rc ? SQLITE_ERROR : SQLITE_OK;
+}
+
+#endif /* SQLITE_OS_UNIX && defined(SQLITE_MUTEX_PTHREADS) */
+/******************************** End Unix Pthreads *************************/
+
+
+/********************************* Single-Threaded **************************/
+#ifndef SQLITE_THREADS_IMPLEMENTED
+/*
+** This implementation does not actually create a new thread.  It does the
+** work of the thread in the main thread, when either the thread is created
+** or when it is joined
+*/
+
+/* A running thread */
+struct SQLiteThread {
+  void *(*xTask)(void*);   /* The routine to run as a thread */
+  void *pIn;               /* Argument to xTask */
+  void *pResult;           /* Result of xTask */
+};
+
+/* Create a new thread */
+int sqlite3ThreadCreate(
+  SQLiteThread **ppThread,  /* OUT: Write the thread object here */
+  void *(*xTask)(void*),    /* Routine to run in a separate thread */
+  void *pIn                 /* Argument passed into xTask() */
+){
+  SQLiteThread *p;
+  *ppThread = p = sqlite3Malloc(sizeof(*p));
+  if( p==0 ) return SQLITE_NOMEM;
+  if( (SQLITE_PTR_TO_INT(p)/17)&1 ){
+    p->xTask = xTask;
+    p->pIn = pIn;
+  }else{
+    p->xTask = 0;
+    p->pResult = xTask(pIn);
+  }
+  return p;
+}
+
+/* Get the results of the thread */
+int sqlite3ThreadJoin(SQLiteThread *p, void **ppOut){
+  if( p==0 ) return SQLITE_NOMEM;
+  if( p->xTask ){
+    *ppOut = = p->xTask(p->pIn);
+  }else{
+    *ppOut = p->pResult;
+  }
+  sqlite3_free(p);
+  return SQLITE_OK;
+}
+
+#endif /* !defined(SQLITE_THREADS_IMPLEMENTED) */
+/****************************** End Single-Threaded *************************/