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From:	Mihail Stefanov <mihaillive AT hotmail DOT com>
Subject:	After call to SwitchToFiber, malloc hangs
Date:	Fri, 3 Jan 2014 12:59:53 +0200
To:	cygwin AT cygwin DOT com
MIME-Version:	1.0 (Mac OS X Mail 7.1 \(1827\))

--Apple-Mail=_9976AB64-04A9-4800-8A40-CFA0632D3C34
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Hi,

I have problem with malloc hanging when I SwitchToFiber. I have current env=
ironment:
=20
CYGWIN_NT-6.1 win7-dev 1.7.27(0.271/5/3) 2013-12-09 11:54 x86_64 Cygwin (Wi=
ndows 7, x64)

I am trying to use Windows Fibers API in cygwin environment. All is working=
 fine, till the moment I call SwitchToFiber and then malloc. The processor =
CPU usage goes to 50% and after some time to 100%. In most cases this a res=
ult of memory corruption.  In case I do not call malloc, all is working fin=
e. Is this something to do with the stack?

I made small test project attached to the email.


--Apple-Mail=_9976AB64-04A9-4800-8A40-CFA0632D3C34
Content-Disposition: attachment; filename="fiber.c"
Content-Type: application/octet-stream; name="fiber.c"
Content-Transfer-Encoding: quoted-printable

#include <assert.h>=0D=0A=
#include "fiber.h"=0D=0A=
=0D=0A=
#define STACK_SIZE (1024*1024)=0D=0A=
=0D=0A=
void=0D=0A=
init_fiber(fiber_t *fiber)=0D=0A=
{=0D=0A=
=0D=0A=
    assert(fiber);=0D=0A=
=0D=0A=
    DWORD ret =3D 0;=0D=0A=
    void *p_fiber =3D 0;=0D=0A=
=0D=0A=
    p_fiber =3D GetCurrentFiber();=0D=0A=
    if (p_fiber !=3D NULL && p_fiber !=3D (void*)0x1E00) {=0D=0A=
        fiber->f_pointer =3D p_fiber;=0D=0A=
        fiber->init =3D 1;=0D=0A=
        return;=0D=0A=
    }=0D=0A=
=0D=0A=
    p_fiber =3D ConvertThreadToFiber(NULL);=0D=0A=
    if(p_fiber) {=0D=0A=
        fiber->f_pointer =3D p_fiber;=0D=0A=
        fiber->init =3D 1;=0D=0A=
    } else {=0D=0A=
        ret =3D GetLastError();=0D=0A=
    }=0D=0A=
}=0D=0A=
=0D=0A=
=0D=0A=
void=0D=0A=
prepare_fiber(size_t stack_size, fiber_t *fiber, void *code, void* arg)=0D=
=0A=
{=0D=0A=
    assert(fiber);=0D=0A=
    assert(code);=0D=0A=
    fiber->f_pointer =3D CreateFiber(stack_size, (LPFIBER_START_ROUTINE)cod=
e, (LPVOID)arg);=0D=0A=
    assert(fiber->f_pointer);=0D=0A=
}=0D=0A=
=0D=0A=
void=0D=0A=
release_fiber(fiber_t *fiber)=0D=0A=
{=0D=0A=
    if (fiber->f_pointer) {=0D=0A=
        DeleteFiber(fiber->f_pointer);=0D=0A=
    }=0D=0A=
    fiber->f_pointer =3D NULL;=0D=0A=
}=0D=0A=
=0D=0A=
void=0D=0A=
switch_fiber(fiber_t *to, fiber_t *from)=0D=0A=
{=0D=0A=
    assert(from->f_pointer);=0D=0A=
    BOOL isFiber =3D IsThreadAFiber();=0D=0A=
    if (!isFiber)=0D=0A=
        ConvertThreadToFiber(0);=0D=0A=
=0D=0A=
    to->f_pointer =3D GetCurrentFiber();=0D=0A=
    SwitchToFiber(from->f_pointer);=0D=0A=
=0D=0A=
    if(!isFiber)=0D=0A=
        ConvertFiberToThread();=0D=0A=
}=0D=0A=
=0D=0A=
void fiber_code(void* arg)=0D=0A=
{=0D=0A=
    void *p =3D malloc(1);=0D=0A=
}=0D=0A=
=0D=0A=
int main(void)=0D=0A=
{=0D=0A=
    fiber_t from;=0D=0A=
    fiber_t to;=0D=0A=
    init_fiber(&from);=0D=0A=
    prepare_fiber(0, &from, fiber_code, 0);=0D=0A=
    switch_fiber(&to, &from);=0D=0A=
=0D=0A=
}=0D=0A=

--Apple-Mail=_9976AB64-04A9-4800-8A40-CFA0632D3C34
Content-Disposition: attachment; filename="fiber.h"
Content-Type: application/octet-stream; name="fiber.h"
Content-Transfer-Encoding: quoted-printable

#ifndef __FIBER_H__=0D=0A=
#define __FIBER_H__=0D=0A=
=0D=0A=
#include <windows.h>=0D=0A=
=0D=0A=
typedef struct _fiber=0D=0A=
{=0D=0A=
        void *f_pointer;=0D=0A=
        int init;=0D=0A=
} fiber_t;=0D=0A=
=0D=0A=
void init_fiber(fiber_t *fiber);=0D=0A=
=0D=0A=
void switch_fiber(fiber_t *to_fiber, fiber_t *from_fiber);=0D=0A=
=0D=0A=
void prepare_fiber(size_t stack_size, fiber_t *fiber, void *code, void* arg=
);=0D=0A=
=0D=0A=
void release_fiber(fiber_t *fiber);=0D=0A=
=0D=0A=
#endif=0D=0A=

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Content-Type: text/plain; charset="us-ascii"



Regards
Mihail

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